https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
/*
 * Copyright (C) 2006 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.reflect;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;

import com.google.common.annotations.Beta;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Joiner;
import com.google.common.base.Predicate;
import com.google.common.collect.FluentIterable;
import com.google.common.collect.ForwardingSet;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Maps;
import com.google.common.collect.Ordering;
import com.google.common.primitives.Primitives;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.Serializable;
import java.lang.reflect.Constructor;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.WildcardType;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
import org.checkerframework.checker.nullness.qual.Nullable;


A Type with generics. 
Operations that are otherwise only available in Class are implemented to support Type, for example isSubtypeOf, isArray and getComponentType. It also provides additional utilities such as getTypes, resolveType, etc. 
There are three ways to get a TypeToken instance: 
    
  
  • Wrap a Type obtained via reflection. For example: 
      TypeToken.of(method.getGenericReturnType()). 
  • Capture a generic type with a (usually anonymous) subclass. For example:
      
    
new TypeToken<List<String>>() {}

    
      
    Note that it's critical that the actual type argument is carried by a subclass. The following code is wrong because it only captures the <T> type variable of the listType() method signature; while <String> is lost in erasure: 
    
class Util {
  static <T> TypeToken<List<T>> listType() {
    return new TypeToken<List<T>>() {};
  }
 }
TypeToken<List<String>> stringListType = Util.<String>listType();

    
  
  • Capture a generic type with a (usually anonymous) subclass and resolve it against a context
      class that knows what the type parameters are. For example:
      
    
abstract class IKnowMyType<T> {
  TypeToken<T> type = new TypeToken<T>(getClass()) {};
 }
new IKnowMyType<String>() {}.type => String

    



TypeToken is serializable when no type variable is contained in the type. 
Note to Guice users:  TypeToken is similar to Guice's TypeLiteral class except that it is serializable and offers numerous additional utility methods. 
Author:Bob Lee, Sven Mawson, Ben Yu
Since:12.0
/**
 * A {@link Type} with generics.
 *
 * <p>Operations that are otherwise only available in {@link Class} are implemented to support
 * {@code Type}, for example {@link #isSubtypeOf}, {@link #isArray} and {@link #getComponentType}.
 * It also provides additional utilities such as {@link #getTypes}, {@link #resolveType}, etc.
 *
 * <p>There are three ways to get a {@code TypeToken} instance:
 *
 * <ul>
 *   <li>Wrap a {@code Type} obtained via reflection. For example: {@code
 *       TypeToken.of(method.getGenericReturnType())}.
 *   <li>Capture a generic type with a (usually anonymous) subclass. For example:
 *       <pre>{@code
 * new TypeToken<List<String>>() {}
 * }</pre>
 *       <p>Note that it's critical that the actual type argument is carried by a subclass. The
 *       following code is wrong because it only captures the {@code <T>} type variable of the
 *       {@code listType()} method signature; while {@code <String>} is lost in erasure:
 *       <pre>{@code
 * class Util {
 *   static <T> TypeToken<List<T>> listType() {
 *     return new TypeToken<List<T>>() {};
 *   }
 * }
 *
 * TypeToken<List<String>> stringListType = Util.<String>listType();
 * }</pre>
 *   <li>Capture a generic type with a (usually anonymous) subclass and resolve it against a context
 *       class that knows what the type parameters are. For example:
 *       <pre>{@code
 * abstract class IKnowMyType<T> {
 *   TypeToken<T> type = new TypeToken<T>(getClass()) {};
 * }
 * new IKnowMyType<String>() {}.type => String
 * }</pre>
 * </ul>
 *
 * <p>{@code TypeToken} is serializable when no type variable is contained in the type.
 *
 * <p>Note to Guice users: {@code} TypeToken is similar to Guice's {@code TypeLiteral} class except
 * that it is serializable and offers numerous additional utility methods.
 *
 * @author Bob Lee
 * @author Sven Mawson
 * @author Ben Yu
 * @since 12.0
 */
@Beta
@SuppressWarnings("serial") // SimpleTypeToken is the serialized form.
public abstract class TypeToken<T> extends TypeCapture<T> implements Serializable {

  private final Type runtimeType;

  
Resolver for resolving parameter and field types with TypeToken<T>.runtimeType as context. 
/** Resolver for resolving parameter and field types with {@link #runtimeType} as context. */
  private transient @MonotonicNonNull TypeResolver invariantTypeResolver;

  
Resolver for resolving covariant types with TypeToken<T>.runtimeType as context. 
/** Resolver for resolving covariant types with {@link #runtimeType} as context. */
  private transient @MonotonicNonNull TypeResolver covariantTypeResolver;

  
Constructs a new type token of T. 
Clients create an empty anonymous subclass. Doing so embeds the type parameter in the
anonymous class's type hierarchy so we can reconstitute it at runtime despite erasure.

For example:


TypeToken<List<String>> t = new TypeToken<List<String>>() {};



/**
   * Constructs a new type token of {@code T}.
   *
   * <p>Clients create an empty anonymous subclass. Doing so embeds the type parameter in the
   * anonymous class's type hierarchy so we can reconstitute it at runtime despite erasure.
   *
   * <p>For example:
   *
   * <pre>{@code
   * TypeToken<List<String>> t = new TypeToken<List<String>>() {};
   * }</pre>
   */
  protected TypeToken() {
    this.runtimeType = capture();
    checkState(
        !(runtimeType instanceof TypeVariable),
        "Cannot construct a TypeToken for a type variable.\n"
            + "You probably meant to call new TypeToken<%s>(getClass()) "
            + "that can resolve the type variable for you.\n"
            + "If you do need to create a TypeToken of a type variable, "
            + "please use TypeToken.of() instead.",
        runtimeType);
  }

  
Constructs a new type token of T while resolving free type variables in the context of declaringClass. 
Clients create an empty anonymous subclass. Doing so embeds the type parameter in the
anonymous class's type hierarchy so we can reconstitute it at runtime despite erasure.

For example:


abstract class IKnowMyType<T> {
  TypeToken<T> getMyType() {
    return new TypeToken<T>(getClass()) {};
  }
 }
new IKnowMyType<String>() {}.getMyType() => String



/**
   * Constructs a new type token of {@code T} while resolving free type variables in the context of
   * {@code declaringClass}.
   *
   * <p>Clients create an empty anonymous subclass. Doing so embeds the type parameter in the
   * anonymous class's type hierarchy so we can reconstitute it at runtime despite erasure.
   *
   * <p>For example:
   *
   * <pre>{@code
   * abstract class IKnowMyType<T> {
   *   TypeToken<T> getMyType() {
   *     return new TypeToken<T>(getClass()) {};
   *   }
   * }
   *
   * new IKnowMyType<String>() {}.getMyType() => String
   * }</pre>
   */
  protected TypeToken(Class<?> declaringClass) {
    Type captured = super.capture();
    if (captured instanceof Class) {
      this.runtimeType = captured;
    } else {
      this.runtimeType = TypeResolver.covariantly(declaringClass).resolveType(captured);
    }
  }

  private TypeToken(Type type) {
    this.runtimeType = checkNotNull(type);
  }

  
Returns an instance of type token that wraps type. 
/** Returns an instance of type token that wraps {@code type}. */
  public static <T> TypeToken<T> of(Class<T> type) {
    return new SimpleTypeToken<T>(type);
  }

  
Returns an instance of type token that wraps type. 
/** Returns an instance of type token that wraps {@code type}. */
  public static TypeToken<?> of(Type type) {
    return new SimpleTypeToken<>(type);
  }

  
Returns the raw type of T. Formally speaking, if T is returned by Method.getGenericReturnType, the raw type is what's returned by Method.getReturnType of the same method object. Specifically: 
    
  
  • If T is a Class itself, T itself is returned. 
  • If T is a ParameterizedType, the raw type of the parameterized type is returned. 
  • If T is a GenericArrayType, the returned type is the corresponding array class. For example: List<Integer>[] => List[]. 
  • If T is a type variable or a wildcard type, the raw type of the first upper bound is returned. For example: <X extends Foo> => Foo. 


/**
   * Returns the raw type of {@code T}. Formally speaking, if {@code T} is returned by {@link
   * java.lang.reflect.Method#getGenericReturnType}, the raw type is what's returned by {@link
   * java.lang.reflect.Method#getReturnType} of the same method object. Specifically:
   *
   * <ul>
   *   <li>If {@code T} is a {@code Class} itself, {@code T} itself is returned.
   *   <li>If {@code T} is a {@link ParameterizedType}, the raw type of the parameterized type is
   *       returned.
   *   <li>If {@code T} is a {@link GenericArrayType}, the returned type is the corresponding array
   *       class. For example: {@code List<Integer>[] => List[]}.
   *   <li>If {@code T} is a type variable or a wildcard type, the raw type of the first upper bound
   *       is returned. For example: {@code <X extends Foo> => Foo}.
   * </ul>
   */
  public final Class<? super T> getRawType() {
    // For wildcard or type variable, the first bound determines the runtime type.
    Class<?> rawType = getRawTypes().iterator().next();
    @SuppressWarnings("unchecked") // raw type is |T|
    Class<? super T> result = (Class<? super T>) rawType;
    return result;
  }

  
Returns the represented type. 
/** Returns the represented type. */
  public final Type getType() {
    return runtimeType;
  }

  
Returns a new TypeToken where type variables represented by typeParam are substituted by typeArg. For example, it can be used to construct Map<K, V> for any K and V type: 

static <K, V> TypeToken<Map<K, V>> mapOf(
    TypeToken<K> keyType, TypeToken<V> valueType) {
  return new TypeToken<Map<K, V>>() {}
      .where(new TypeParameter<K>() {}, keyType)
      .where(new TypeParameter<V>() {}, valueType);
 }



Params:
  • typeParam – the parameter type variable
  • typeArg – the actual type to substitute
Type parameters:
  • <X> – The parameter type
/**
   * Returns a new {@code TypeToken} where type variables represented by {@code typeParam} are
   * substituted by {@code typeArg}. For example, it can be used to construct {@code Map<K, V>} for
   * any {@code K} and {@code V} type:
   *
   * <pre>{@code
   * static <K, V> TypeToken<Map<K, V>> mapOf(
   *     TypeToken<K> keyType, TypeToken<V> valueType) {
   *   return new TypeToken<Map<K, V>>() {}
   *       .where(new TypeParameter<K>() {}, keyType)
   *       .where(new TypeParameter<V>() {}, valueType);
   * }
   * }</pre>
   *
   * @param <X> The parameter type
   * @param typeParam the parameter type variable
   * @param typeArg the actual type to substitute
   */
  public final <X> TypeToken<T> where(TypeParameter<X> typeParam, TypeToken<X> typeArg) {
    TypeResolver resolver =
        new TypeResolver()
            .where(
                ImmutableMap.of(
                    new TypeResolver.TypeVariableKey(typeParam.typeVariable), typeArg.runtimeType));
    // If there's any type error, we'd report now rather than later.
    return new SimpleTypeToken<T>(resolver.resolveType(runtimeType));
  }

  
Returns a new TypeToken where type variables represented by typeParam are substituted by typeArg. For example, it can be used to construct Map<K, V> for any K and V type: 

static <K, V> TypeToken<Map<K, V>> mapOf(
    Class<K> keyType, Class<V> valueType) {
  return new TypeToken<Map<K, V>>() {}
      .where(new TypeParameter<K>() {}, keyType)
      .where(new TypeParameter<V>() {}, valueType);
 }



Params:
  • typeParam – the parameter type variable
  • typeArg – the actual type to substitute
Type parameters:
  • <X> – The parameter type
/**
   * Returns a new {@code TypeToken} where type variables represented by {@code typeParam} are
   * substituted by {@code typeArg}. For example, it can be used to construct {@code Map<K, V>} for
   * any {@code K} and {@code V} type:
   *
   * <pre>{@code
   * static <K, V> TypeToken<Map<K, V>> mapOf(
   *     Class<K> keyType, Class<V> valueType) {
   *   return new TypeToken<Map<K, V>>() {}
   *       .where(new TypeParameter<K>() {}, keyType)
   *       .where(new TypeParameter<V>() {}, valueType);
   * }
   * }</pre>
   *
   * @param <X> The parameter type
   * @param typeParam the parameter type variable
   * @param typeArg the actual type to substitute
   */
  public final <X> TypeToken<T> where(TypeParameter<X> typeParam, Class<X> typeArg) {
    return where(typeParam, of(typeArg));
  }

  
Resolves the given type against the type context represented by this type. For example: 

new TypeToken<List<String>>() {}.resolveType(
    List.class.getMethod("get", int.class).getGenericReturnType())
=> String.class



/**
   * Resolves the given {@code type} against the type context represented by this type. For example:
   *
   * <pre>{@code
   * new TypeToken<List<String>>() {}.resolveType(
   *     List.class.getMethod("get", int.class).getGenericReturnType())
   * => String.class
   * }</pre>
   */
  public final TypeToken<?> resolveType(Type type) {
    checkNotNull(type);
    // Being conservative here because the user could use resolveType() to resolve a type in an
    // invariant context.
    return of(getInvariantTypeResolver().resolveType(type));
  }

  private TypeToken<?> resolveSupertype(Type type) {
    TypeToken<?> supertype = of(getCovariantTypeResolver().resolveType(type));
    // super types' type mapping is a subset of type mapping of this type.
    supertype.covariantTypeResolver = covariantTypeResolver;
    supertype.invariantTypeResolver = invariantTypeResolver;
    return supertype;
  }

  
Returns the generic superclass of this type or null if the type represents Object or an interface. This method is similar but different from Class.getGenericSuperclass. For example, new TypeToken<StringArrayList>()
{}.getGenericSuperclass() will return new TypeToken<ArrayList<String>>() {}; while StringArrayList.class.getGenericSuperclass() will return ArrayList<E>, where E is the type variable declared by class ArrayList. 
If this type is a type variable or wildcard, its first upper bound is examined and returned
if the bound is a class or extends from a class. This means that the returned type could be a
type variable too.

/**
   * Returns the generic superclass of this type or {@code null} if the type represents {@link
   * Object} or an interface. This method is similar but different from {@link
   * Class#getGenericSuperclass}. For example, {@code new TypeToken<StringArrayList>()
   * {}.getGenericSuperclass()} will return {@code new TypeToken<ArrayList<String>>() {}}; while
   * {@code StringArrayList.class.getGenericSuperclass()} will return {@code ArrayList<E>}, where
   * {@code E} is the type variable declared by class {@code ArrayList}.
   *
   * <p>If this type is a type variable or wildcard, its first upper bound is examined and returned
   * if the bound is a class or extends from a class. This means that the returned type could be a
   * type variable too.
   */
  final @Nullable TypeToken<? super T> getGenericSuperclass() {
    if (runtimeType instanceof TypeVariable) {
      // First bound is always the super class, if one exists.
      return boundAsSuperclass(((TypeVariable<?>) runtimeType).getBounds()[0]);
    }
    if (runtimeType instanceof WildcardType) {
      // wildcard has one and only one upper bound.
      return boundAsSuperclass(((WildcardType) runtimeType).getUpperBounds()[0]);
    }
    Type superclass = getRawType().getGenericSuperclass();
    if (superclass == null) {
      return null;
    }
    @SuppressWarnings("unchecked") // super class of T
    TypeToken<? super T> superToken = (TypeToken<? super T>) resolveSupertype(superclass);
    return superToken;
  }

  private @Nullable TypeToken<? super T> boundAsSuperclass(Type bound) {
    TypeToken<?> token = of(bound);
    if (token.getRawType().isInterface()) {
      return null;
    }
    @SuppressWarnings("unchecked") // only upper bound of T is passed in.
    TypeToken<? super T> superclass = (TypeToken<? super T>) token;
    return superclass;
  }

  
Returns the generic interfaces that this type directly implements. This method is similar but different from Class.getGenericInterfaces(). For example, new
TypeToken<List<String>>() {}.getGenericInterfaces() will return a list that contains 
new TypeToken<Iterable<String>>() {}; while List.class.getGenericInterfaces() will return an array that contains Iterable<T>, where the T is the type variable declared by interface Iterable. 
If this type is a type variable or wildcard, its upper bounds are examined and those that
are either an interface or upper-bounded only by interfaces are returned. This means that the
returned types could include type variables too.

/**
   * Returns the generic interfaces that this type directly {@code implements}. This method is
   * similar but different from {@link Class#getGenericInterfaces()}. For example, {@code new
   * TypeToken<List<String>>() {}.getGenericInterfaces()} will return a list that contains {@code
   * new TypeToken<Iterable<String>>() {}}; while {@code List.class.getGenericInterfaces()} will
   * return an array that contains {@code Iterable<T>}, where the {@code T} is the type variable
   * declared by interface {@code Iterable}.
   *
   * <p>If this type is a type variable or wildcard, its upper bounds are examined and those that
   * are either an interface or upper-bounded only by interfaces are returned. This means that the
   * returned types could include type variables too.
   */
  final ImmutableList<TypeToken<? super T>> getGenericInterfaces() {
    if (runtimeType instanceof TypeVariable) {
      return boundsAsInterfaces(((TypeVariable<?>) runtimeType).getBounds());
    }
    if (runtimeType instanceof WildcardType) {
      return boundsAsInterfaces(((WildcardType) runtimeType).getUpperBounds());
    }
    ImmutableList.Builder<TypeToken<? super T>> builder = ImmutableList.builder();
    for (Type interfaceType : getRawType().getGenericInterfaces()) {
      @SuppressWarnings("unchecked") // interface of T
      TypeToken<? super T> resolvedInterface =
          (TypeToken<? super T>) resolveSupertype(interfaceType);
      builder.add(resolvedInterface);
    }
    return builder.build();
  }

  private ImmutableList<TypeToken<? super T>> boundsAsInterfaces(Type[] bounds) {
    ImmutableList.Builder<TypeToken<? super T>> builder = ImmutableList.builder();
    for (Type bound : bounds) {
      @SuppressWarnings("unchecked") // upper bound of T
      TypeToken<? super T> boundType = (TypeToken<? super T>) of(bound);
      if (boundType.getRawType().isInterface()) {
        builder.add(boundType);
      }
    }
    return builder.build();
  }

  
Returns the set of interfaces and classes that this type is or is a subtype of. The returned
types are parameterized with proper type arguments.

Subtypes are always listed before supertypes. But the reverse is not true. A type isn't
necessarily a subtype of all the types following. Order between types without subtype
relationship is arbitrary and not guaranteed.

If this type is a type variable or wildcard, upper bounds that are themselves type variables
aren't included (their super interfaces and superclasses are).

/**
   * Returns the set of interfaces and classes that this type is or is a subtype of. The returned
   * types are parameterized with proper type arguments.
   *
   * <p>Subtypes are always listed before supertypes. But the reverse is not true. A type isn't
   * necessarily a subtype of all the types following. Order between types without subtype
   * relationship is arbitrary and not guaranteed.
   *
   * <p>If this type is a type variable or wildcard, upper bounds that are themselves type variables
   * aren't included (their super interfaces and superclasses are).
   */
  public final TypeSet getTypes() {
    return new TypeSet();
  }

  
Returns the generic form of superclass. For example, if this is 
ArrayList<String>, Iterable<String> is returned given the input 
Iterable.class. 
/**
   * Returns the generic form of {@code superclass}. For example, if this is {@code
   * ArrayList<String>}, {@code Iterable<String>} is returned given the input {@code
   * Iterable.class}.
   */
  public final TypeToken<? super T> getSupertype(Class<? super T> superclass) {
    checkArgument(
        this.someRawTypeIsSubclassOf(superclass),
        "%s is not a super class of %s",
        superclass,
        this);
    if (runtimeType instanceof TypeVariable) {
      return getSupertypeFromUpperBounds(superclass, ((TypeVariable<?>) runtimeType).getBounds());
    }
    if (runtimeType instanceof WildcardType) {
      return getSupertypeFromUpperBounds(superclass, ((WildcardType) runtimeType).getUpperBounds());
    }
    if (superclass.isArray()) {
      return getArraySupertype(superclass);
    }
    @SuppressWarnings("unchecked") // resolved supertype
    TypeToken<? super T> supertype =
        (TypeToken<? super T>) resolveSupertype(toGenericType(superclass).runtimeType);
    return supertype;
  }

  
Returns subtype of this with subclass as the raw class. For example, if this is Iterable<String> and subclass is List, List<String> is returned. 
/**
   * Returns subtype of {@code this} with {@code subclass} as the raw class. For example, if this is
   * {@code Iterable<String>} and {@code subclass} is {@code List}, {@code List<String>} is
   * returned.
   */
  public final TypeToken<? extends T> getSubtype(Class<?> subclass) {
    checkArgument(
        !(runtimeType instanceof TypeVariable), "Cannot get subtype of type variable <%s>", this);
    if (runtimeType instanceof WildcardType) {
      return getSubtypeFromLowerBounds(subclass, ((WildcardType) runtimeType).getLowerBounds());
    }
    // unwrap array type if necessary
    if (isArray()) {
      return getArraySubtype(subclass);
    }
    // At this point, it's either a raw class or parameterized type.
    checkArgument(
        getRawType().isAssignableFrom(subclass), "%s isn't a subclass of %s", subclass, this);
    Type resolvedTypeArgs = resolveTypeArgsForSubclass(subclass);
    @SuppressWarnings("unchecked") // guarded by the isAssignableFrom() statement above
    TypeToken<? extends T> subtype = (TypeToken<? extends T>) of(resolvedTypeArgs);
    checkArgument(
        subtype.isSubtypeOf(this), "%s does not appear to be a subtype of %s", subtype, this);
    return subtype;
  }

  
Returns true if this type is a supertype of the given type. "Supertype" is defined according to the rules for type
arguments introduced with Java generics.

Since:19.0
/**
   * Returns true if this type is a supertype of the given {@code type}. "Supertype" is defined
   * according to <a
   * href="http://docs.oracle.com/javase/specs/jls/se8/html/jls-4.html#jls-4.5.1">the rules for type
   * arguments</a> introduced with Java generics.
   *
   * @since 19.0
   */
  public final boolean isSupertypeOf(TypeToken<?> type) {
    return type.isSubtypeOf(getType());
  }

  
Returns true if this type is a supertype of the given type. "Supertype" is defined according to the rules for type
arguments introduced with Java generics.

Since:19.0
/**
   * Returns true if this type is a supertype of the given {@code type}. "Supertype" is defined
   * according to <a
   * href="http://docs.oracle.com/javase/specs/jls/se8/html/jls-4.html#jls-4.5.1">the rules for type
   * arguments</a> introduced with Java generics.
   *
   * @since 19.0
   */
  public final boolean isSupertypeOf(Type type) {
    return of(type).isSubtypeOf(getType());
  }

  
Returns true if this type is a subtype of the given type. "Subtype" is defined according to the rules for type
arguments introduced with Java generics.

Since:19.0
/**
   * Returns true if this type is a subtype of the given {@code type}. "Subtype" is defined
   * according to <a
   * href="http://docs.oracle.com/javase/specs/jls/se8/html/jls-4.html#jls-4.5.1">the rules for type
   * arguments</a> introduced with Java generics.
   *
   * @since 19.0
   */
  public final boolean isSubtypeOf(TypeToken<?> type) {
    return isSubtypeOf(type.getType());
  }

  
Returns true if this type is a subtype of the given type. "Subtype" is defined according to the rules for type
arguments introduced with Java generics.

Since:19.0
/**
   * Returns true if this type is a subtype of the given {@code type}. "Subtype" is defined
   * according to <a
   * href="http://docs.oracle.com/javase/specs/jls/se8/html/jls-4.html#jls-4.5.1">the rules for type
   * arguments</a> introduced with Java generics.
   *
   * @since 19.0
   */
  public final boolean isSubtypeOf(Type supertype) {
    checkNotNull(supertype);
    if (supertype instanceof WildcardType) {
      // if 'supertype' is <? super Foo>, 'this' can be:
      // Foo, SubFoo, <? extends Foo>.
      // if 'supertype' is <? extends Foo>, nothing is a subtype.
      return any(((WildcardType) supertype).getLowerBounds()).isSupertypeOf(runtimeType);
    }
    // if 'this' is wildcard, it's a suptype of to 'supertype' if any of its "extends"
    // bounds is a subtype of 'supertype'.
    if (runtimeType instanceof WildcardType) {
      // <? super Base> is of no use in checking 'from' being a subtype of 'to'.
      return any(((WildcardType) runtimeType).getUpperBounds()).isSubtypeOf(supertype);
    }
    // if 'this' is type variable, it's a subtype if any of its "extends"
    // bounds is a subtype of 'supertype'.
    if (runtimeType instanceof TypeVariable) {
      return runtimeType.equals(supertype)
          || any(((TypeVariable<?>) runtimeType).getBounds()).isSubtypeOf(supertype);
    }
    if (runtimeType instanceof GenericArrayType) {
      return of(supertype).isSupertypeOfArray((GenericArrayType) runtimeType);
    }
    // Proceed to regular Type subtype check
    if (supertype instanceof Class) {
      return this.someRawTypeIsSubclassOf((Class<?>) supertype);
    } else if (supertype instanceof ParameterizedType) {
      return this.isSubtypeOfParameterizedType((ParameterizedType) supertype);
    } else if (supertype instanceof GenericArrayType) {
      return this.isSubtypeOfArrayType((GenericArrayType) supertype);
    } else { // to instanceof TypeVariable
      return false;
    }
  }

  
Returns true if this type is known to be an array type, such as int[], T[], <? extends Map<String, Integer>[]> etc. 
/**
   * Returns true if this type is known to be an array type, such as {@code int[]}, {@code T[]},
   * {@code <? extends Map<String, Integer>[]>} etc.
   */
  public final boolean isArray() {
    return getComponentType() != null;
  }

  
Returns true if this type is one of the nine primitive types (including void). 
Since:15.0
/**
   * Returns true if this type is one of the nine primitive types (including {@code void}).
   *
   * @since 15.0
   */
  public final boolean isPrimitive() {
    return (runtimeType instanceof Class) && ((Class<?>) runtimeType).isPrimitive();
  }

  
Returns the corresponding wrapper type if this is a primitive type; otherwise returns 
this itself. Idempotent. 
Since:15.0
/**
   * Returns the corresponding wrapper type if this is a primitive type; otherwise returns {@code
   * this} itself. Idempotent.
   *
   * @since 15.0
   */
  public final TypeToken<T> wrap() {
    if (isPrimitive()) {
      @SuppressWarnings("unchecked") // this is a primitive class
      Class<T> type = (Class<T>) runtimeType;
      return of(Primitives.wrap(type));
    }
    return this;
  }

  private boolean isWrapper() {
    return Primitives.allWrapperTypes().contains(runtimeType);
  }

  
Returns the corresponding primitive type if this is a wrapper type; otherwise returns 
this itself. Idempotent. 
Since:15.0
/**
   * Returns the corresponding primitive type if this is a wrapper type; otherwise returns {@code
   * this} itself. Idempotent.
   *
   * @since 15.0
   */
  public final TypeToken<T> unwrap() {
    if (isWrapper()) {
      @SuppressWarnings("unchecked") // this is a wrapper class
      Class<T> type = (Class<T>) runtimeType;
      return of(Primitives.unwrap(type));
    }
    return this;
  }

  
Returns the array component type if this type represents an array (int[], T[], <? extends Map<String, Integer>[]> etc.), or else null is returned. 
/**
   * Returns the array component type if this type represents an array ({@code int[]}, {@code T[]},
   * {@code <? extends Map<String, Integer>[]>} etc.), or else {@code null} is returned.
   */
  public final @Nullable TypeToken<?> getComponentType() {
    Type componentType = Types.getComponentType(runtimeType);
    if (componentType == null) {
      return null;
    }
    return of(componentType);
  }

  
Returns the Invokable for method, which must be a member of T. 
Since:14.0
/**
   * Returns the {@link Invokable} for {@code method}, which must be a member of {@code T}.
   *
   * @since 14.0
   */
  public final Invokable<T, Object> method(Method method) {
    checkArgument(
        this.someRawTypeIsSubclassOf(method.getDeclaringClass()),
        "%s not declared by %s",
        method,
        this);
    return new Invokable.MethodInvokable<T>(method) {
      @Override
      Type getGenericReturnType() {
        return getCovariantTypeResolver().resolveType(super.getGenericReturnType());
      }

      @Override
      Type[] getGenericParameterTypes() {
        return getInvariantTypeResolver().resolveTypesInPlace(super.getGenericParameterTypes());
      }

      @Override
      Type[] getGenericExceptionTypes() {
        return getCovariantTypeResolver().resolveTypesInPlace(super.getGenericExceptionTypes());
      }

      @Override
      public TypeToken<T> getOwnerType() {
        return TypeToken.this;
      }

      @Override
      public String toString() {
        return getOwnerType() + "." + super.toString();
      }
    };
  }

  
Returns the Invokable for constructor, which must be a member of T. 
Since:14.0
/**
   * Returns the {@link Invokable} for {@code constructor}, which must be a member of {@code T}.
   *
   * @since 14.0
   */
  public final Invokable<T, T> constructor(Constructor<?> constructor) {
    checkArgument(
        constructor.getDeclaringClass() == getRawType(),
        "%s not declared by %s",
        constructor,
        getRawType());
    return new Invokable.ConstructorInvokable<T>(constructor) {
      @Override
      Type getGenericReturnType() {
        return getCovariantTypeResolver().resolveType(super.getGenericReturnType());
      }

      @Override
      Type[] getGenericParameterTypes() {
        return getInvariantTypeResolver().resolveTypesInPlace(super.getGenericParameterTypes());
      }

      @Override
      Type[] getGenericExceptionTypes() {
        return getCovariantTypeResolver().resolveTypesInPlace(super.getGenericExceptionTypes());
      }

      @Override
      public TypeToken<T> getOwnerType() {
        return TypeToken.this;
      }

      @Override
      public String toString() {
        return getOwnerType() + "(" + Joiner.on(", ").join(getGenericParameterTypes()) + ")";
      }
    };
  }

  
The set of interfaces and classes that T is or is a subtype of. Object is not included in the set if this type is an interface. 
Since:13.0
/**
   * The set of interfaces and classes that {@code T} is or is a subtype of. {@link Object} is not
   * included in the set if this type is an interface.
   *
   * @since 13.0
   */
  public class TypeSet extends ForwardingSet<TypeToken<? super T>> implements Serializable {

    private transient @MonotonicNonNull ImmutableSet<TypeToken<? super T>> types;

    TypeSet() {}

    
Returns the types that are interfaces implemented by this type. 
/** Returns the types that are interfaces implemented by this type. */
    public TypeSet interfaces() {
      return new InterfaceSet(this);
    }

    
Returns the types that are classes. 
/** Returns the types that are classes. */
    public TypeSet classes() {
      return new ClassSet();
    }

    @Override
    protected Set<TypeToken<? super T>> delegate() {
      ImmutableSet<TypeToken<? super T>> filteredTypes = types;
      if (filteredTypes == null) {
        // Java has no way to express ? super T when we parameterize TypeToken vs. Class.
        @SuppressWarnings({"unchecked", "rawtypes"})
        ImmutableList<TypeToken<? super T>> collectedTypes =
            (ImmutableList) TypeCollector.FOR_GENERIC_TYPE.collectTypes(TypeToken.this);
        return (types =
            FluentIterable.from(collectedTypes)
                .filter(TypeFilter.IGNORE_TYPE_VARIABLE_OR_WILDCARD)
                .toSet());
      } else {
        return filteredTypes;
      }
    }

    
Returns the raw types of the types in this set, in the same order. 
/** Returns the raw types of the types in this set, in the same order. */
    public Set<Class<? super T>> rawTypes() {
      // Java has no way to express ? super T when we parameterize TypeToken vs. Class.
      @SuppressWarnings({"unchecked", "rawtypes"})
      ImmutableList<Class<? super T>> collectedTypes =
          (ImmutableList) TypeCollector.FOR_RAW_TYPE.collectTypes(getRawTypes());
      return ImmutableSet.copyOf(collectedTypes);
    }

    private static final long serialVersionUID = 0;
  }

  private final class InterfaceSet extends TypeSet {

    private final transient TypeSet allTypes;
    private transient @MonotonicNonNull ImmutableSet<TypeToken<? super T>> interfaces;

    InterfaceSet(TypeSet allTypes) {
      this.allTypes = allTypes;
    }

    @Override
    protected Set<TypeToken<? super T>> delegate() {
      ImmutableSet<TypeToken<? super T>> result = interfaces;
      if (result == null) {
        return (interfaces =
            FluentIterable.from(allTypes).filter(TypeFilter.INTERFACE_ONLY).toSet());
      } else {
        return result;
      }
    }

    @Override
    public TypeSet interfaces() {
      return this;
    }

    @Override
    public Set<Class<? super T>> rawTypes() {
      // Java has no way to express ? super T when we parameterize TypeToken vs. Class.
      @SuppressWarnings({"unchecked", "rawtypes"})
      ImmutableList<Class<? super T>> collectedTypes =
          (ImmutableList) TypeCollector.FOR_RAW_TYPE.collectTypes(getRawTypes());
      return FluentIterable.from(collectedTypes)
          .filter(
              new Predicate<Class<?>>() {
                @Override
                public boolean apply(Class<?> type) {
                  return type.isInterface();
                }
              })
          .toSet();
    }

    @Override
    public TypeSet classes() {
      throw new UnsupportedOperationException("interfaces().classes() not supported.");
    }

    private Object readResolve() {
      return getTypes().interfaces();
    }

    private static final long serialVersionUID = 0;
  }

  private final class ClassSet extends TypeSet {

    private transient @MonotonicNonNull ImmutableSet<TypeToken<? super T>> classes;

    @Override
    protected Set<TypeToken<? super T>> delegate() {
      ImmutableSet<TypeToken<? super T>> result = classes;
      if (result == null) {
        @SuppressWarnings({"unchecked", "rawtypes"})
        ImmutableList<TypeToken<? super T>> collectedTypes =
            (ImmutableList)
                TypeCollector.FOR_GENERIC_TYPE.classesOnly().collectTypes(TypeToken.this);
        return (classes =
            FluentIterable.from(collectedTypes)
                .filter(TypeFilter.IGNORE_TYPE_VARIABLE_OR_WILDCARD)
                .toSet());
      } else {
        return result;
      }
    }

    @Override
    public TypeSet classes() {
      return this;
    }

    @Override
    public Set<Class<? super T>> rawTypes() {
      // Java has no way to express ? super T when we parameterize TypeToken vs. Class.
      @SuppressWarnings({"unchecked", "rawtypes"})
      ImmutableList<Class<? super T>> collectedTypes =
          (ImmutableList) TypeCollector.FOR_RAW_TYPE.classesOnly().collectTypes(getRawTypes());
      return ImmutableSet.copyOf(collectedTypes);
    }

    @Override
    public TypeSet interfaces() {
      throw new UnsupportedOperationException("classes().interfaces() not supported.");
    }

    private Object readResolve() {
      return getTypes().classes();
    }

    private static final long serialVersionUID = 0;
  }

  private enum TypeFilter implements Predicate<TypeToken<?>> {
    IGNORE_TYPE_VARIABLE_OR_WILDCARD {
      @Override
      public boolean apply(TypeToken<?> type) {
        return !(type.runtimeType instanceof TypeVariable
            || type.runtimeType instanceof WildcardType);
      }
    },
    INTERFACE_ONLY {
      @Override
      public boolean apply(TypeToken<?> type) {
        return type.getRawType().isInterface();
      }
    }
  }

  
Returns true if o is another TypeToken that represents the same Type. 
/**
   * Returns true if {@code o} is another {@code TypeToken} that represents the same {@link Type}.
   */
  @Override
  public boolean equals(@Nullable Object o) {
    if (o instanceof TypeToken) {
      TypeToken<?> that = (TypeToken<?>) o;
      return runtimeType.equals(that.runtimeType);
    }
    return false;
  }

  @Override
  public int hashCode() {
    return runtimeType.hashCode();
  }

  @Override
  public String toString() {
    return Types.toString(runtimeType);
  }

  
Implemented to support serialization of subclasses. 
/** Implemented to support serialization of subclasses. */
  protected Object writeReplace() {
    // TypeResolver just transforms the type to our own impls that are Serializable
    // except TypeVariable.
    return of(new TypeResolver().resolveType(runtimeType));
  }

  
Ensures that this type token doesn't contain type variables, which can cause unchecked type errors for callers like TypeToInstanceMap. 
/**
   * Ensures that this type token doesn't contain type variables, which can cause unchecked type
   * errors for callers like {@link TypeToInstanceMap}.
   */
  @CanIgnoreReturnValue
  final TypeToken<T> rejectTypeVariables() {
    new TypeVisitor() {
      @Override
      void visitTypeVariable(TypeVariable<?> type) {
        throw new IllegalArgumentException(
            runtimeType + "contains a type variable and is not safe for the operation");
      }

      @Override
      void visitWildcardType(WildcardType type) {
        visit(type.getLowerBounds());
        visit(type.getUpperBounds());
      }

      @Override
      void visitParameterizedType(ParameterizedType type) {
        visit(type.getActualTypeArguments());
        visit(type.getOwnerType());
      }

      @Override
      void visitGenericArrayType(GenericArrayType type) {
        visit(type.getGenericComponentType());
      }
    }.visit(runtimeType);
    return this;
  }

  private boolean someRawTypeIsSubclassOf(Class<?> superclass) {
    for (Class<?> rawType : getRawTypes()) {
      if (superclass.isAssignableFrom(rawType)) {
        return true;
      }
    }
    return false;
  }

  private boolean isSubtypeOfParameterizedType(ParameterizedType supertype) {
    Class<?> matchedClass = of(supertype).getRawType();
    if (!someRawTypeIsSubclassOf(matchedClass)) {
      return false;
    }
    TypeVariable<?>[] typeVars = matchedClass.getTypeParameters();
    Type[] supertypeArgs = supertype.getActualTypeArguments();
    for (int i = 0; i < typeVars.length; i++) {
      Type subtypeParam = getCovariantTypeResolver().resolveType(typeVars[i]);
      // If 'supertype' is "List<? extends CharSequence>"
      // and 'this' is StringArrayList,
      // First step is to figure out StringArrayList "is-a" List<E> where <E> = String.
      // String is then matched against <? extends CharSequence>, the supertypeArgs[0].
      if (!of(subtypeParam).is(supertypeArgs[i], typeVars[i])) {
        return false;
      }
    }
    // We only care about the case when the supertype is a non-static inner class
    // in which case we need to make sure the subclass's owner type is a subtype of the
    // supertype's owner.
    return Modifier.isStatic(((Class<?>) supertype.getRawType()).getModifiers())
        || supertype.getOwnerType() == null
        || isOwnedBySubtypeOf(supertype.getOwnerType());
  }

  private boolean isSubtypeOfArrayType(GenericArrayType supertype) {
    if (runtimeType instanceof Class) {
      Class<?> fromClass = (Class<?>) runtimeType;
      if (!fromClass.isArray()) {
        return false;
      }
      return of(fromClass.getComponentType()).isSubtypeOf(supertype.getGenericComponentType());
    } else if (runtimeType instanceof GenericArrayType) {
      GenericArrayType fromArrayType = (GenericArrayType) runtimeType;
      return of(fromArrayType.getGenericComponentType())
          .isSubtypeOf(supertype.getGenericComponentType());
    } else {
      return false;
    }
  }

  private boolean isSupertypeOfArray(GenericArrayType subtype) {
    if (runtimeType instanceof Class) {
      Class<?> thisClass = (Class<?>) runtimeType;
      if (!thisClass.isArray()) {
        return thisClass.isAssignableFrom(Object[].class);
      }
      return of(subtype.getGenericComponentType()).isSubtypeOf(thisClass.getComponentType());
    } else if (runtimeType instanceof GenericArrayType) {
      return of(subtype.getGenericComponentType())
          .isSubtypeOf(((GenericArrayType) runtimeType).getGenericComponentType());
    } else {
      return false;
    }
  }

  
A.is(B) is defined as Foo<A>.isSubtypeOf(Foo<B>). 
Specifically, returns true if any of the following conditions is met:

    
  
  1. 'this' and formalType are equal. 
  2. 'this' and formalType have equal canonical form. 
  3. formalType is <? extends Foo> and 'this' is a subtype of Foo. 
  4. formalType is <? super Foo> and 'this' is a supertype of Foo. 
 Note that condition 2 isn't technically accurate under the context of a recursively bounded type variables. For example, Enum<? extends Enum<E>> canonicalizes to Enum<?> where E is the type variable declared on the Enum class declaration. It's technically not true that Foo<Enum<? extends Enum<E>>> is a subtype of Foo<Enum<?>> according to JLS. See testRecursiveWildcardSubtypeBug() for a real example. 
It appears that properly handling recursive type bounds in the presence of implicit type
bounds is not easy. For now we punt, hoping that this defect should rarely cause issues in real
code.

Params:
  • formalType – is Foo<formalType> a supertype of Foo<T>?
  • declaration – The type variable in the context of a parameterized type. Used to infer type bound when formalType is a wildcard with implicit upper bound.
/**
   * {@code A.is(B)} is defined as {@code Foo<A>.isSubtypeOf(Foo<B>)}.
   *
   * <p>Specifically, returns true if any of the following conditions is met:
   * <ol>
   *   <li>'this' and {@code formalType} are equal.
   *   <li>'this' and {@code formalType} have equal canonical form.
   *   <li>{@code formalType} is {@code <? extends Foo>} and 'this' is a subtype of {@code Foo}.
   *   <li>{@code formalType} is {@code <? super Foo>} and 'this' is a supertype of {@code Foo}.
   * </ol>
   * Note that condition 2 isn't technically accurate under the context of a recursively
   * bounded type variables. For example, {@code Enum<? extends Enum<E>>} canonicalizes to
   * {@code Enum<?>} where {@code E} is the type variable declared on the {@code Enum} class
   * declaration. It's technically <em>not</em> true that {@code Foo<Enum<? extends Enum<E>>>} is a
   * subtype of {@code Foo<Enum<?>>} according to JLS. See testRecursiveWildcardSubtypeBug() for
   * a real example.
   *
   * <p>It appears that properly handling recursive type bounds in the presence of implicit type
   * bounds is not easy. For now we punt, hoping that this defect should rarely cause issues in real
   * code.
   *
   * @param formalType is {@code Foo<formalType>} a supertype of {@code Foo<T>}?
   * @param declaration The type variable in the context of a parameterized type. Used to infer
   *        type bound when {@code formalType} is a wildcard with implicit upper bound.
   */
  private boolean is(Type formalType, TypeVariable<?> declaration) {
    if (runtimeType.equals(formalType)) {
      return true;
    }
    if (formalType instanceof WildcardType) {
      WildcardType your = canonicalizeWildcardType(declaration, (WildcardType) formalType);
      // if "formalType" is <? extends Foo>, "this" can be:
      // Foo, SubFoo, <? extends Foo>, <? extends SubFoo>, <T extends Foo> or
      // <T extends SubFoo>.
      // if "formalType" is <? super Foo>, "this" can be:
      // Foo, SuperFoo, <? super Foo> or <? super SuperFoo>.
      return every(your.getUpperBounds()).isSupertypeOf(runtimeType)
          && every(your.getLowerBounds()).isSubtypeOf(runtimeType);
    }
    return canonicalizeWildcardsInType(runtimeType)
        .equals(canonicalizeWildcardsInType(formalType));
  }

  
In reflection, Foo<?>.getUpperBounds()[0] is always Object.class, even when Foo is defined as Foo<T extends String>. Thus directly calling <?>.is(String.class) will return false. To mitigate, we canonicalize wildcards by enforcing the following invariants: 
    

  1. canonicalize(t) always produces the equal result for equivalent types. For example both Enum<?> and Enum<? extends Enum<?>> canonicalize to Enum<? extends Enum<E>. 
  2. canonicalize(t) produces a "literal" supertype of t. For example: Enum<? extends Enum<?>> canonicalizes to Enum<?>, which is a supertype (if we disregard the upper bound is implicitly an Enum too). 
  3. If canonicalize(A) == canonicalize(B), then Foo<A>.isSubtypeOf(Foo<B>) and vice versa. i.e. A.is(B) and B.is(A). 
  4. canonicalize(canonicalize(A)) == canonicalize(A). 


/**
   * In reflection, {@code Foo<?>.getUpperBounds()[0]} is always {@code Object.class}, even when Foo
   * is defined as {@code Foo<T extends String>}. Thus directly calling {@code <?>.is(String.class)}
   * will return false. To mitigate, we canonicalize wildcards by enforcing the following
   * invariants:
   * <ol>
   * <li>{@code canonicalize(t)} always produces the equal result for equivalent types. For example
   *     both {@code Enum<?>} and {@code Enum<? extends Enum<?>>} canonicalize to
   *     {@code Enum<? extends Enum<E>}.
   * <li>{@code canonicalize(t)} produces a "literal" supertype of t.
   *     For example: {@code Enum<? extends Enum<?>>} canonicalizes to {@code Enum<?>}, which is
   *     a supertype (if we disregard the upper bound is implicitly an Enum too).
   * <li>If {@code canonicalize(A) == canonicalize(B)}, then {@code Foo<A>.isSubtypeOf(Foo<B>)} and
   *     vice versa. i.e. {@code A.is(B)} and {@code B.is(A)}.
   * <li>{@code canonicalize(canonicalize(A)) == canonicalize(A)}.
   * </ol>
   */
  private static Type canonicalizeTypeArg(TypeVariable<?> declaration, Type typeArg) {
    return typeArg instanceof WildcardType
        ? canonicalizeWildcardType(declaration, ((WildcardType) typeArg))
        : canonicalizeWildcardsInType(typeArg);
  }

  private static Type canonicalizeWildcardsInType(Type type) {
    if (type instanceof ParameterizedType) {
      return canonicalizeWildcardsInParameterizedType((ParameterizedType) type);
    }
    if (type instanceof GenericArrayType) {
      return Types.newArrayType(
          canonicalizeWildcardsInType(((GenericArrayType) type).getGenericComponentType()));
    }
    return type;
  }

  // WARNING: the returned type may have empty upper bounds, which may violate common expectations
  // by user code or even some of our own code. It's fine for the purpose of checking subtypes.
  // Just don't ever let the user access it.
  private static WildcardType canonicalizeWildcardType(
      TypeVariable<?> declaration, WildcardType type) {
    Type[] declared = declaration.getBounds();
    List<Type> upperBounds = new ArrayList<>();
    for (Type bound : type.getUpperBounds()) {
      if (!any(declared).isSubtypeOf(bound)) {
        upperBounds.add(canonicalizeWildcardsInType(bound));
      }
    }
    return new Types.WildcardTypeImpl(type.getLowerBounds(), upperBounds.toArray(new Type[0]));
  }

  private static ParameterizedType canonicalizeWildcardsInParameterizedType(
      ParameterizedType type) {
    Class<?> rawType = (Class<?>) type.getRawType();
    TypeVariable<?>[] typeVars = rawType.getTypeParameters();
    Type[] typeArgs = type.getActualTypeArguments();
    for (int i = 0; i < typeArgs.length; i++) {
      typeArgs[i] = canonicalizeTypeArg(typeVars[i], typeArgs[i]);
    }
    return Types.newParameterizedTypeWithOwner(type.getOwnerType(), rawType, typeArgs);
  }

  private static Bounds every(Type[] bounds) {
    // Every bound must match. On any false, result is false.
    return new Bounds(bounds, false);
  }

  private static Bounds any(Type[] bounds) {
    // Any bound matches. On any true, result is true.
    return new Bounds(bounds, true);
  }

  private static class Bounds {
    private final Type[] bounds;
    private final boolean target;

    Bounds(Type[] bounds, boolean target) {
      this.bounds = bounds;
      this.target = target;
    }

    boolean isSubtypeOf(Type supertype) {
      for (Type bound : bounds) {
        if (of(bound).isSubtypeOf(supertype) == target) {
          return target;
        }
      }
      return !target;
    }

    boolean isSupertypeOf(Type subtype) {
      TypeToken<?> type = of(subtype);
      for (Type bound : bounds) {
        if (type.isSubtypeOf(bound) == target) {
          return target;
        }
      }
      return !target;
    }
  }

  private ImmutableSet<Class<? super T>> getRawTypes() {
    final ImmutableSet.Builder<Class<?>> builder = ImmutableSet.builder();
    new TypeVisitor() {
      @Override
      void visitTypeVariable(TypeVariable<?> t) {
        visit(t.getBounds());
      }

      @Override
      void visitWildcardType(WildcardType t) {
        visit(t.getUpperBounds());
      }

      @Override
      void visitParameterizedType(ParameterizedType t) {
        builder.add((Class<?>) t.getRawType());
      }

      @Override
      void visitClass(Class<?> t) {
        builder.add(t);
      }

      @Override
      void visitGenericArrayType(GenericArrayType t) {
        builder.add(Types.getArrayClass(of(t.getGenericComponentType()).getRawType()));
      }
    }.visit(runtimeType);
    // Cast from ImmutableSet<Class<?>> to ImmutableSet<Class<? super T>>
    @SuppressWarnings({"unchecked", "rawtypes"})
    ImmutableSet<Class<? super T>> result = (ImmutableSet) builder.build();
    return result;
  }

  private boolean isOwnedBySubtypeOf(Type supertype) {
    for (TypeToken<?> type : getTypes()) {
      Type ownerType = type.getOwnerTypeIfPresent();
      if (ownerType != null && of(ownerType).isSubtypeOf(supertype)) {
        return true;
      }
    }
    return false;
  }

  
Returns the owner type of a ParameterizedType or enclosing class of a Class, or null otherwise. 
/**
   * Returns the owner type of a {@link ParameterizedType} or enclosing class of a {@link Class}, or
   * null otherwise.
   */
  private @Nullable Type getOwnerTypeIfPresent() {
    if (runtimeType instanceof ParameterizedType) {
      return ((ParameterizedType) runtimeType).getOwnerType();
    } else if (runtimeType instanceof Class<?>) {
      return ((Class<?>) runtimeType).getEnclosingClass();
    } else {
      return null;
    }
  }

  
Returns the type token representing the generic type declaration of cls. For example: TypeToken.getGenericType(Iterable.class) returns Iterable<T>. 
If cls isn't parameterized and isn't a generic array, the type token of the class is returned. 
/**
   * Returns the type token representing the generic type declaration of {@code cls}. For example:
   * {@code TypeToken.getGenericType(Iterable.class)} returns {@code Iterable<T>}.
   *
   * <p>If {@code cls} isn't parameterized and isn't a generic array, the type token of the class is
   * returned.
   */
  @VisibleForTesting
  static <T> TypeToken<? extends T> toGenericType(Class<T> cls) {
    if (cls.isArray()) {
      Type arrayOfGenericType =
          Types.newArrayType(
              // If we are passed with int[].class, don't turn it to GenericArrayType
              toGenericType(cls.getComponentType()).runtimeType);
      @SuppressWarnings("unchecked") // array is covariant
      TypeToken<? extends T> result = (TypeToken<? extends T>) of(arrayOfGenericType);
      return result;
    }
    TypeVariable<Class<T>>[] typeParams = cls.getTypeParameters();
    Type ownerType =
        cls.isMemberClass() && !Modifier.isStatic(cls.getModifiers())
            ? toGenericType(cls.getEnclosingClass()).runtimeType
            : null;

    if ((typeParams.length > 0) || ((ownerType != null) && ownerType != cls.getEnclosingClass())) {
      @SuppressWarnings("unchecked") // Like, it's Iterable<T> for Iterable.class
      TypeToken<? extends T> type =
          (TypeToken<? extends T>)
              of(Types.newParameterizedTypeWithOwner(ownerType, cls, typeParams));
      return type;
    } else {
      return of(cls);
    }
  }

  private TypeResolver getCovariantTypeResolver() {
    TypeResolver resolver = covariantTypeResolver;
    if (resolver == null) {
      resolver = (covariantTypeResolver = TypeResolver.covariantly(runtimeType));
    }
    return resolver;
  }

  private TypeResolver getInvariantTypeResolver() {
    TypeResolver resolver = invariantTypeResolver;
    if (resolver == null) {
      resolver = (invariantTypeResolver = TypeResolver.invariantly(runtimeType));
    }
    return resolver;
  }

  private TypeToken<? super T> getSupertypeFromUpperBounds(
      Class<? super T> supertype, Type[] upperBounds) {
    for (Type upperBound : upperBounds) {
      @SuppressWarnings("unchecked") // T's upperbound is <? super T>.
      TypeToken<? super T> bound = (TypeToken<? super T>) of(upperBound);
      if (bound.isSubtypeOf(supertype)) {
        @SuppressWarnings({"rawtypes", "unchecked"}) // guarded by the isSubtypeOf check.
        TypeToken<? super T> result = bound.getSupertype((Class) supertype);
        return result;
      }
    }
    throw new IllegalArgumentException(supertype + " isn't a super type of " + this);
  }

  private TypeToken<? extends T> getSubtypeFromLowerBounds(Class<?> subclass, Type[] lowerBounds) {
    for (Type lowerBound : lowerBounds) {
      @SuppressWarnings("unchecked") // T's lower bound is <? extends T>
      TypeToken<? extends T> bound = (TypeToken<? extends T>) of(lowerBound);
      // Java supports only one lowerbound anyway.
      return bound.getSubtype(subclass);
    }
    throw new IllegalArgumentException(subclass + " isn't a subclass of " + this);
  }

  private TypeToken<? super T> getArraySupertype(Class<? super T> supertype) {
    // with component type, we have lost generic type information
    // Use raw type so that compiler allows us to call getSupertype()
    @SuppressWarnings("rawtypes")
    TypeToken componentType =
        checkNotNull(getComponentType(), "%s isn't a super type of %s", supertype, this);
    // array is covariant. component type is super type, so is the array type.
    @SuppressWarnings("unchecked") // going from raw type back to generics
    TypeToken<?> componentSupertype = componentType.getSupertype(supertype.getComponentType());
    @SuppressWarnings("unchecked") // component type is super type, so is array type.
    TypeToken<? super T> result =
        (TypeToken<? super T>)
            // If we are passed with int[].class, don't turn it to GenericArrayType
            of(newArrayClassOrGenericArrayType(componentSupertype.runtimeType));
    return result;
  }

  private TypeToken<? extends T> getArraySubtype(Class<?> subclass) {
    // array is covariant. component type is subtype, so is the array type.
    TypeToken<?> componentSubtype = getComponentType().getSubtype(subclass.getComponentType());
    @SuppressWarnings("unchecked") // component type is subtype, so is array type.
    TypeToken<? extends T> result =
        (TypeToken<? extends T>)
            // If we are passed with int[].class, don't turn it to GenericArrayType
            of(newArrayClassOrGenericArrayType(componentSubtype.runtimeType));
    return result;
  }

  private Type resolveTypeArgsForSubclass(Class<?> subclass) {
    // If both runtimeType and subclass are not parameterized, return subclass
    // If runtimeType is not parameterized but subclass is, process subclass as a parameterized type
    // If runtimeType is a raw type (i.e. is a parameterized type specified as a Class<?>), we
    // return subclass as a raw type
    if (runtimeType instanceof Class
        && ((subclass.getTypeParameters().length == 0)
            || (getRawType().getTypeParameters().length != 0))) {
      // no resolution needed
      return subclass;
    }
    // class Base<A, B> {}
    // class Sub<X, Y> extends Base<X, Y> {}
    // Base<String, Integer>.subtype(Sub.class):

    // Sub<X, Y>.getSupertype(Base.class) => Base<X, Y>
    // => X=String, Y=Integer
    // => Sub<X, Y>=Sub<String, Integer>
    TypeToken<?> genericSubtype = toGenericType(subclass);
    @SuppressWarnings({"rawtypes", "unchecked"}) // subclass isn't <? extends T>
    Type supertypeWithArgsFromSubtype =
        genericSubtype.getSupertype((Class) getRawType()).runtimeType;
    return new TypeResolver()
        .where(supertypeWithArgsFromSubtype, runtimeType)
        .resolveType(genericSubtype.runtimeType);
  }

  
Creates an array class if componentType is a class, or else, a GenericArrayType. This is what Java7 does for generic array type parameters. 
/**
   * Creates an array class if {@code componentType} is a class, or else, a {@link
   * GenericArrayType}. This is what Java7 does for generic array type parameters.
   */
  private static Type newArrayClassOrGenericArrayType(Type componentType) {
    return Types.JavaVersion.JAVA7.newArrayType(componentType);
  }

  private static final class SimpleTypeToken<T> extends TypeToken<T> {

    SimpleTypeToken(Type type) {
      super(type);
    }

    private static final long serialVersionUID = 0;
  }

  
Collects parent types from a sub type.

Type parameters:
  • <K> – The type "kind". Either a TypeToken, or Class.
/**
   * Collects parent types from a sub type.
   *
   * @param <K> The type "kind". Either a TypeToken, or Class.
   */
  private abstract static class TypeCollector<K> {

    static final TypeCollector<TypeToken<?>> FOR_GENERIC_TYPE =
        new TypeCollector<TypeToken<?>>() {
          @Override
          Class<?> getRawType(TypeToken<?> type) {
            return type.getRawType();
          }

          @Override
          Iterable<? extends TypeToken<?>> getInterfaces(TypeToken<?> type) {
            return type.getGenericInterfaces();
          }

          @Override
          @Nullable
          TypeToken<?> getSuperclass(TypeToken<?> type) {
            return type.getGenericSuperclass();
          }
        };

    static final TypeCollector<Class<?>> FOR_RAW_TYPE =
        new TypeCollector<Class<?>>() {
          @Override
          Class<?> getRawType(Class<?> type) {
            return type;
          }

          @Override
          Iterable<? extends Class<?>> getInterfaces(Class<?> type) {
            return Arrays.asList(type.getInterfaces());
          }

          @Override
          @Nullable
          Class<?> getSuperclass(Class<?> type) {
            return type.getSuperclass();
          }
        };

    
For just classes, we don't have to traverse interfaces. 
/** For just classes, we don't have to traverse interfaces. */
    final TypeCollector<K> classesOnly() {
      return new ForwardingTypeCollector<K>(this) {
        @Override
        Iterable<? extends K> getInterfaces(K type) {
          return ImmutableSet.of();
        }

        @Override
        ImmutableList<K> collectTypes(Iterable<? extends K> types) {
          ImmutableList.Builder<K> builder = ImmutableList.builder();
          for (K type : types) {
            if (!getRawType(type).isInterface()) {
              builder.add(type);
            }
          }
          return super.collectTypes(builder.build());
        }
      };
    }

    final ImmutableList<K> collectTypes(K type) {
      return collectTypes(ImmutableList.of(type));
    }

    ImmutableList<K> collectTypes(Iterable<? extends K> types) {
      // type -> order number. 1 for Object, 2 for anything directly below, so on so forth.
      Map<K, Integer> map = Maps.newHashMap();
      for (K type : types) {
        collectTypes(type, map);
      }
      return sortKeysByValue(map, Ordering.natural().reverse());
    }

    
Collects all types to map, and returns the total depth from T up to Object. 
/** Collects all types to map, and returns the total depth from T up to Object. */
    @CanIgnoreReturnValue
    private int collectTypes(K type, Map<? super K, Integer> map) {
      Integer existing = map.get(type);
      if (existing != null) {
        // short circuit: if set contains type it already contains its supertypes
        return existing;
      }
      // Interfaces should be listed before Object.
      int aboveMe = getRawType(type).isInterface() ? 1 : 0;
      for (K interfaceType : getInterfaces(type)) {
        aboveMe = Math.max(aboveMe, collectTypes(interfaceType, map));
      }
      K superclass = getSuperclass(type);
      if (superclass != null) {
        aboveMe = Math.max(aboveMe, collectTypes(superclass, map));
      }
      /*
       * TODO(benyu): should we include Object for interface? Also, CharSequence[] and Object[] for
       * String[]?
       *
       */
      map.put(type, aboveMe + 1);
      return aboveMe + 1;
    }

    private static <K, V> ImmutableList<K> sortKeysByValue(
        final Map<K, V> map, final Comparator<? super V> valueComparator) {
      Ordering<K> keyOrdering =
          new Ordering<K>() {
            @Override
            public int compare(K left, K right) {
              return valueComparator.compare(map.get(left), map.get(right));
            }
          };
      return keyOrdering.immutableSortedCopy(map.keySet());
    }

    abstract Class<?> getRawType(K type);

    abstract Iterable<? extends K> getInterfaces(K type);

    abstract @Nullable K getSuperclass(K type);

    private static class ForwardingTypeCollector<K> extends TypeCollector<K> {

      private final TypeCollector<K> delegate;

      ForwardingTypeCollector(TypeCollector<K> delegate) {
        this.delegate = delegate;
      }

      @Override
      Class<?> getRawType(K type) {
        return delegate.getRawType(type);
      }

      @Override
      Iterable<? extends K> getInterfaces(K type) {
        return delegate.getInterfaces(type);
      }

      @Override
      K getSuperclass(K type) {
        return delegate.getSuperclass(type);
      }
    }
  }

  // This happens to be the hash of the class as of now. So setting it makes a backward compatible
  // change. Going forward, if any incompatible change is added, we can change the UID back to 1.
  private static final long serialVersionUID = 3637540370352322684L;
}