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) 2011 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.collect.Iterables.transform;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Function;
import com.google.common.base.Joiner;
import com.google.common.base.Objects;
import com.google.common.base.Predicates;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Iterables;
import java.io.Serializable;
import java.lang.reflect.AnnotatedElement;
import java.lang.reflect.Array;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.GenericDeclaration;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Proxy;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.WildcardType;
import java.security.AccessControlException;
import java.util.Arrays;
import java.util.Collection;
import java.util.Map.Entry;
import java.util.concurrent.atomic.AtomicReference;
import org.checkerframework.checker.nullness.qual.Nullable;


Utilities for working with Type. 
Author:Ben Yu
/**
 * Utilities for working with {@link Type}.
 *
 * @author Ben Yu
 */
final class Types {

  
Class#toString without the "class " and "interface " prefixes 
/** Class#toString without the "class " and "interface " prefixes */
  private static final Function<Type, String> TYPE_NAME =
      new Function<Type, String>() {
        @Override
        public String apply(Type from) {
          return JavaVersion.CURRENT.typeName(from);
        }
      };

  private static final Joiner COMMA_JOINER = Joiner.on(", ").useForNull("null");

  
Returns the array type of componentType. 
/** Returns the array type of {@code componentType}. */
  static Type newArrayType(Type componentType) {
    if (componentType instanceof WildcardType) {
      WildcardType wildcard = (WildcardType) componentType;
      Type[] lowerBounds = wildcard.getLowerBounds();
      checkArgument(lowerBounds.length <= 1, "Wildcard cannot have more than one lower bounds.");
      if (lowerBounds.length == 1) {
        return supertypeOf(newArrayType(lowerBounds[0]));
      } else {
        Type[] upperBounds = wildcard.getUpperBounds();
        checkArgument(upperBounds.length == 1, "Wildcard should have only one upper bound.");
        return subtypeOf(newArrayType(upperBounds[0]));
      }
    }
    return JavaVersion.CURRENT.newArrayType(componentType);
  }

  
Returns a type where rawType is parameterized by arguments and is owned by ownerType. 
/**
   * Returns a type where {@code rawType} is parameterized by {@code arguments} and is owned by
   * {@code ownerType}.
   */
  static ParameterizedType newParameterizedTypeWithOwner(
      @Nullable Type ownerType, Class<?> rawType, Type... arguments) {
    if (ownerType == null) {
      return newParameterizedType(rawType, arguments);
    }
    // ParameterizedTypeImpl constructor already checks, but we want to throw NPE before IAE
    checkNotNull(arguments);
    checkArgument(rawType.getEnclosingClass() != null, "Owner type for unenclosed %s", rawType);
    return new ParameterizedTypeImpl(ownerType, rawType, arguments);
  }

  
Returns a type where rawType is parameterized by arguments. 
/** Returns a type where {@code rawType} is parameterized by {@code arguments}. */
  static ParameterizedType newParameterizedType(Class<?> rawType, Type... arguments) {
    return new ParameterizedTypeImpl(
        ClassOwnership.JVM_BEHAVIOR.getOwnerType(rawType), rawType, arguments);
  }

  
Decides what owner type to use for constructing ParameterizedType from a raw class. 
/** Decides what owner type to use for constructing {@link ParameterizedType} from a raw class. */
  private enum ClassOwnership {
    OWNED_BY_ENCLOSING_CLASS {
      @Override
      @Nullable
      Class<?> getOwnerType(Class<?> rawType) {
        return rawType.getEnclosingClass();
      }
    },
    LOCAL_CLASS_HAS_NO_OWNER {
      @Override
      @Nullable
      Class<?> getOwnerType(Class<?> rawType) {
        if (rawType.isLocalClass()) {
          return null;
        } else {
          return rawType.getEnclosingClass();
        }
      }
    };

    abstract @Nullable Class<?> getOwnerType(Class<?> rawType);

    static final ClassOwnership JVM_BEHAVIOR = detectJvmBehavior();

    private static ClassOwnership detectJvmBehavior() {
      class LocalClass<T> {}
      Class<?> subclass = new LocalClass<String>() {}.getClass();
      ParameterizedType parameterizedType = (ParameterizedType) subclass.getGenericSuperclass();
      for (ClassOwnership behavior : ClassOwnership.values()) {
        if (behavior.getOwnerType(LocalClass.class) == parameterizedType.getOwnerType()) {
          return behavior;
        }
      }
      throw new AssertionError();
    }
  }

  
Returns a new TypeVariable that belongs to declaration with name and bounds. 
/**
   * Returns a new {@link TypeVariable} that belongs to {@code declaration} with {@code name} and
   * {@code bounds}.
   */
  static <D extends GenericDeclaration> TypeVariable<D> newArtificialTypeVariable(
      D declaration, String name, Type... bounds) {
    return newTypeVariableImpl(
        declaration, name, (bounds.length == 0) ? new Type[] {Object.class} : bounds);
  }

  
Returns a new WildcardType with upperBound. 
/** Returns a new {@link WildcardType} with {@code upperBound}. */
  @VisibleForTesting
  static WildcardType subtypeOf(Type upperBound) {
    return new WildcardTypeImpl(new Type[0], new Type[] {upperBound});
  }

  
Returns a new WildcardType with lowerBound. 
/** Returns a new {@link WildcardType} with {@code lowerBound}. */
  @VisibleForTesting
  static WildcardType supertypeOf(Type lowerBound) {
    return new WildcardTypeImpl(new Type[] {lowerBound}, new Type[] {Object.class});
  }

  
Returns human readable string representation of type. 
The format is subject to change.

/**
   * Returns human readable string representation of {@code type}.
   *
   * <p>The format is subject to change.
   */
  static String toString(Type type) {
    return (type instanceof Class) ? ((Class<?>) type).getName() : type.toString();
  }

  static @Nullable Type getComponentType(Type type) {
    checkNotNull(type);
    final AtomicReference<Type> result = new AtomicReference<>();
    new TypeVisitor() {
      @Override
      void visitTypeVariable(TypeVariable<?> t) {
        result.set(subtypeOfComponentType(t.getBounds()));
      }

      @Override
      void visitWildcardType(WildcardType t) {
        result.set(subtypeOfComponentType(t.getUpperBounds()));
      }

      @Override
      void visitGenericArrayType(GenericArrayType t) {
        result.set(t.getGenericComponentType());
      }

      @Override
      void visitClass(Class<?> t) {
        result.set(t.getComponentType());
      }
    }.visit(type);
    return result.get();
  }

  
Returns ? extends X if any of bounds is a subtype of X[]; or null otherwise. 
/**
   * Returns {@code ? extends X} if any of {@code bounds} is a subtype of {@code X[]}; or null
   * otherwise.
   */
  private static @Nullable Type subtypeOfComponentType(Type[] bounds) {
    for (Type bound : bounds) {
      Type componentType = getComponentType(bound);
      if (componentType != null) {
        // Only the first bound can be a class or array.
        // Bounds after the first can only be interfaces.
        if (componentType instanceof Class) {
          Class<?> componentClass = (Class<?>) componentType;
          if (componentClass.isPrimitive()) {
            return componentClass;
          }
        }
        return subtypeOf(componentType);
      }
    }
    return null;
  }

  private static final class GenericArrayTypeImpl implements GenericArrayType, Serializable {

    private final Type componentType;

    GenericArrayTypeImpl(Type componentType) {
      this.componentType = JavaVersion.CURRENT.usedInGenericType(componentType);
    }

    @Override
    public Type getGenericComponentType() {
      return componentType;
    }

    @Override
    public String toString() {
      return Types.toString(componentType) + "[]";
    }

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

    @Override
    public boolean equals(Object obj) {
      if (obj instanceof GenericArrayType) {
        GenericArrayType that = (GenericArrayType) obj;
        return Objects.equal(getGenericComponentType(), that.getGenericComponentType());
      }
      return false;
    }

    private static final long serialVersionUID = 0;
  }

  private static final class ParameterizedTypeImpl implements ParameterizedType, Serializable {

    private final @Nullable Type ownerType;
    private final ImmutableList<Type> argumentsList;
    private final Class<?> rawType;

    ParameterizedTypeImpl(@Nullable Type ownerType, Class<?> rawType, Type[] typeArguments) {
      checkNotNull(rawType);
      checkArgument(typeArguments.length == rawType.getTypeParameters().length);
      disallowPrimitiveType(typeArguments, "type parameter");
      this.ownerType = ownerType;
      this.rawType = rawType;
      this.argumentsList = JavaVersion.CURRENT.usedInGenericType(typeArguments);
    }

    @Override
    public Type[] getActualTypeArguments() {
      return toArray(argumentsList);
    }

    @Override
    public Type getRawType() {
      return rawType;
    }

    @Override
    public Type getOwnerType() {
      return ownerType;
    }

    @Override
    public String toString() {
      StringBuilder builder = new StringBuilder();
      if (ownerType != null && JavaVersion.CURRENT.jdkTypeDuplicatesOwnerName()) {
        builder.append(JavaVersion.CURRENT.typeName(ownerType)).append('.');
      }
      return builder
          .append(rawType.getName())
          .append('<')
          .append(COMMA_JOINER.join(transform(argumentsList, TYPE_NAME)))
          .append('>')
          .toString();
    }

    @Override
    public int hashCode() {
      return (ownerType == null ? 0 : ownerType.hashCode())
          ^ argumentsList.hashCode()
          ^ rawType.hashCode();
    }

    @Override
    public boolean equals(Object other) {
      if (!(other instanceof ParameterizedType)) {
        return false;
      }
      ParameterizedType that = (ParameterizedType) other;
      return getRawType().equals(that.getRawType())
          && Objects.equal(getOwnerType(), that.getOwnerType())
          && Arrays.equals(getActualTypeArguments(), that.getActualTypeArguments());
    }

    private static final long serialVersionUID = 0;
  }

  private static <D extends GenericDeclaration> TypeVariable<D> newTypeVariableImpl(
      D genericDeclaration, String name, Type[] bounds) {
    TypeVariableImpl<D> typeVariableImpl =
        new TypeVariableImpl<D>(genericDeclaration, name, bounds);
    @SuppressWarnings("unchecked")
    TypeVariable<D> typeVariable =
        Reflection.newProxy(
            TypeVariable.class, new TypeVariableInvocationHandler(typeVariableImpl));
    return typeVariable;
  }

  
Invocation handler to work around a compatibility problem between Java 7 and Java 8.

Java 8 introduced a new method getAnnotatedBounds() in the TypeVariable interface, whose return type AnnotatedType[] is also new in Java 8. That means that we cannot implement that interface in source code in a way that will compile on both Java 7 and Java 8. If we include the getAnnotatedBounds() method then its return type means it won't compile on Java 7, while if we don't include the method then the compiler will complain that an abstract method is unimplemented. So instead we use a dynamic proxy to get an implementation. If the method being called on the TypeVariable instance has the same name as one of the public methods of TypeVariableImpl, the proxy calls the same method on its instance of TypeVariableImpl. Otherwise it throws UnsupportedOperationException; this should only apply to getAnnotatedBounds(). This does mean that users on Java 8 who obtain an instance of TypeVariable from TypeResolver.resolveType will not be able to call getAnnotatedBounds() on it, but that should hopefully be rare. 
TODO(b/147144588): We are currently also missing the methods inherited from AnnotatedElement, which TypeVariable began to extend only in Java 8. Those methods refer only to types present in Java 7, so we could implement them in TypeVariableImpl today. (We could probably then make TypeVariableImpl implement AnnotatedElement so that we get partial compile-time checking.) 
This workaround should be removed at a distant future time when we no longer support Java
versions earlier than 8.

/**
   * Invocation handler to work around a compatibility problem between Java 7 and Java 8.
   *
   * <p>Java 8 introduced a new method {@code getAnnotatedBounds()} in the {@link TypeVariable}
   * interface, whose return type {@code AnnotatedType[]} is also new in Java 8. That means that we
   * cannot implement that interface in source code in a way that will compile on both Java 7 and
   * Java 8. If we include the {@code getAnnotatedBounds()} method then its return type means it
   * won't compile on Java 7, while if we don't include the method then the compiler will complain
   * that an abstract method is unimplemented. So instead we use a dynamic proxy to get an
   * implementation. If the method being called on the {@code TypeVariable} instance has the same
   * name as one of the public methods of {@link TypeVariableImpl}, the proxy calls the same method
   * on its instance of {@code TypeVariableImpl}. Otherwise it throws {@link
   * UnsupportedOperationException}; this should only apply to {@code getAnnotatedBounds()}. This
   * does mean that users on Java 8 who obtain an instance of {@code TypeVariable} from {@link
   * TypeResolver#resolveType} will not be able to call {@code getAnnotatedBounds()} on it, but that
   * should hopefully be rare.
   *
   * <p>TODO(b/147144588): We are currently also missing the methods inherited from {@link
   * AnnotatedElement}, which {@code TypeVariable} began to extend only in Java 8. Those methods
   * refer only to types present in Java 7, so we could implement them in {@code TypeVariableImpl}
   * today. (We could probably then make {@code TypeVariableImpl} implement {@code AnnotatedElement}
   * so that we get partial compile-time checking.)
   *
   * <p>This workaround should be removed at a distant future time when we no longer support Java
   * versions earlier than 8.
   */
  private static final class TypeVariableInvocationHandler implements InvocationHandler {
    private static final ImmutableMap<String, Method> typeVariableMethods;

    static {
      ImmutableMap.Builder<String, Method> builder = ImmutableMap.builder();
      for (Method method : TypeVariableImpl.class.getMethods()) {
        if (method.getDeclaringClass().equals(TypeVariableImpl.class)) {
          try {
            method.setAccessible(true);
          } catch (AccessControlException e) {
            // OK: the method is accessible to us anyway. The setAccessible call is only for
            // unusual execution environments where that might not be true.
          }
          builder.put(method.getName(), method);
        }
      }
      typeVariableMethods = builder.build();
    }

    private final TypeVariableImpl<?> typeVariableImpl;

    TypeVariableInvocationHandler(TypeVariableImpl<?> typeVariableImpl) {
      this.typeVariableImpl = typeVariableImpl;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
      String methodName = method.getName();
      Method typeVariableMethod = typeVariableMethods.get(methodName);
      if (typeVariableMethod == null) {
        throw new UnsupportedOperationException(methodName);
      } else {
        try {
          return typeVariableMethod.invoke(typeVariableImpl, args);
        } catch (InvocationTargetException e) {
          throw e.getCause();
        }
      }
    }
  }

  private static final class TypeVariableImpl<D extends GenericDeclaration> {

    private final D genericDeclaration;
    private final String name;
    private final ImmutableList<Type> bounds;

    TypeVariableImpl(D genericDeclaration, String name, Type[] bounds) {
      disallowPrimitiveType(bounds, "bound for type variable");
      this.genericDeclaration = checkNotNull(genericDeclaration);
      this.name = checkNotNull(name);
      this.bounds = ImmutableList.copyOf(bounds);
    }

    public Type[] getBounds() {
      return toArray(bounds);
    }

    public D getGenericDeclaration() {
      return genericDeclaration;
    }

    public String getName() {
      return name;
    }

    public String getTypeName() {
      return name;
    }

    @Override
    public String toString() {
      return name;
    }

    @Override
    public int hashCode() {
      return genericDeclaration.hashCode() ^ name.hashCode();
    }

    @Override
    public boolean equals(Object obj) {
      if (NativeTypeVariableEquals.NATIVE_TYPE_VARIABLE_ONLY) {
        // equal only to our TypeVariable implementation with identical bounds
        if (obj != null
            && Proxy.isProxyClass(obj.getClass())
            && Proxy.getInvocationHandler(obj) instanceof TypeVariableInvocationHandler) {
          TypeVariableInvocationHandler typeVariableInvocationHandler =
              (TypeVariableInvocationHandler) Proxy.getInvocationHandler(obj);
          TypeVariableImpl<?> that = typeVariableInvocationHandler.typeVariableImpl;
          return name.equals(that.getName())
              && genericDeclaration.equals(that.getGenericDeclaration())
              && bounds.equals(that.bounds);
        }
        return false;
      } else {
        // equal to any TypeVariable implementation regardless of bounds
        if (obj instanceof TypeVariable) {
          TypeVariable<?> that = (TypeVariable<?>) obj;
          return name.equals(that.getName())
              && genericDeclaration.equals(that.getGenericDeclaration());
        }
        return false;
      }
    }
  }

  static final class WildcardTypeImpl implements WildcardType, Serializable {

    private final ImmutableList<Type> lowerBounds;
    private final ImmutableList<Type> upperBounds;

    WildcardTypeImpl(Type[] lowerBounds, Type[] upperBounds) {
      disallowPrimitiveType(lowerBounds, "lower bound for wildcard");
      disallowPrimitiveType(upperBounds, "upper bound for wildcard");
      this.lowerBounds = JavaVersion.CURRENT.usedInGenericType(lowerBounds);
      this.upperBounds = JavaVersion.CURRENT.usedInGenericType(upperBounds);
    }

    @Override
    public Type[] getLowerBounds() {
      return toArray(lowerBounds);
    }

    @Override
    public Type[] getUpperBounds() {
      return toArray(upperBounds);
    }

    @Override
    public boolean equals(Object obj) {
      if (obj instanceof WildcardType) {
        WildcardType that = (WildcardType) obj;
        return lowerBounds.equals(Arrays.asList(that.getLowerBounds()))
            && upperBounds.equals(Arrays.asList(that.getUpperBounds()));
      }
      return false;
    }

    @Override
    public int hashCode() {
      return lowerBounds.hashCode() ^ upperBounds.hashCode();
    }

    @Override
    public String toString() {
      StringBuilder builder = new StringBuilder("?");
      for (Type lowerBound : lowerBounds) {
        builder.append(" super ").append(JavaVersion.CURRENT.typeName(lowerBound));
      }
      for (Type upperBound : filterUpperBounds(upperBounds)) {
        builder.append(" extends ").append(JavaVersion.CURRENT.typeName(upperBound));
      }
      return builder.toString();
    }

    private static final long serialVersionUID = 0;
  }

  private static Type[] toArray(Collection<Type> types) {
    return types.toArray(new Type[0]);
  }

  private static Iterable<Type> filterUpperBounds(Iterable<Type> bounds) {
    return Iterables.filter(bounds, Predicates.not(Predicates.<Type>equalTo(Object.class)));
  }

  private static void disallowPrimitiveType(Type[] types, String usedAs) {
    for (Type type : types) {
      if (type instanceof Class) {
        Class<?> cls = (Class<?>) type;
        checkArgument(!cls.isPrimitive(), "Primitive type '%s' used as %s", cls, usedAs);
      }
    }
  }

  
Returns the Class object of arrays with componentType. 
/** Returns the {@code Class} object of arrays with {@code componentType}. */
  static Class<?> getArrayClass(Class<?> componentType) {
    // TODO(user): This is not the most efficient way to handle generic
    // arrays, but is there another way to extract the array class in a
    // non-hacky way (i.e. using String value class names- "[L...")?
    return Array.newInstance(componentType, 0).getClass();
  }

  // TODO(benyu): Once behavior is the same for all Java versions we support, delete this.
  enum JavaVersion {
    JAVA6 {
      @Override
      GenericArrayType newArrayType(Type componentType) {
        return new GenericArrayTypeImpl(componentType);
      }

      @Override
      Type usedInGenericType(Type type) {
        checkNotNull(type);
        if (type instanceof Class) {
          Class<?> cls = (Class<?>) type;
          if (cls.isArray()) {
            return new GenericArrayTypeImpl(cls.getComponentType());
          }
        }
        return type;
      }
    },
    JAVA7 {
      @Override
      Type newArrayType(Type componentType) {
        if (componentType instanceof Class) {
          return getArrayClass((Class<?>) componentType);
        } else {
          return new GenericArrayTypeImpl(componentType);
        }
      }

      @Override
      Type usedInGenericType(Type type) {
        return checkNotNull(type);
      }
    },
    JAVA8 {
      @Override
      Type newArrayType(Type componentType) {
        return JAVA7.newArrayType(componentType);
      }

      @Override
      Type usedInGenericType(Type type) {
        return JAVA7.usedInGenericType(type);
      }

      @Override
      String typeName(Type type) {
        try {
          Method getTypeName = Type.class.getMethod("getTypeName");
          return (String) getTypeName.invoke(type);
        } catch (NoSuchMethodException e) {
          throw new AssertionError("Type.getTypeName should be available in Java 8");
          /*
           * Do not merge the 2 catch blocks below. javac would infer a type of
           * ReflectiveOperationException, which Animal Sniffer would reject. (Old versions of
           * Android don't *seem* to mind, but there might be edge cases of which we're unaware.)
           */
        } catch (InvocationTargetException e) {
          throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
          throw new RuntimeException(e);
        }
      }
    },
    JAVA9 {
      @Override
      Type newArrayType(Type componentType) {
        return JAVA8.newArrayType(componentType);
      }

      @Override
      Type usedInGenericType(Type type) {
        return JAVA8.usedInGenericType(type);
      }

      @Override
      String typeName(Type type) {
        return JAVA8.typeName(type);
      }

      @Override
      boolean jdkTypeDuplicatesOwnerName() {
        return false;
      }
    };

    static final JavaVersion CURRENT;

    static {
      if (AnnotatedElement.class.isAssignableFrom(TypeVariable.class)) {
        if (new TypeCapture<Entry<String, int[][]>>() {}.capture()
            .toString()
            .contains("java.util.Map.java.util.Map")) {
          CURRENT = JAVA8;
        } else {
          CURRENT = JAVA9;
        }
      } else if (new TypeCapture<int[]>() {}.capture() instanceof Class) {
        CURRENT = JAVA7;
      } else {
        CURRENT = JAVA6;
      }
    }

    abstract Type newArrayType(Type componentType);

    abstract Type usedInGenericType(Type type);

    final ImmutableList<Type> usedInGenericType(Type[] types) {
      ImmutableList.Builder<Type> builder = ImmutableList.builder();
      for (Type type : types) {
        builder.add(usedInGenericType(type));
      }
      return builder.build();
    }

    String typeName(Type type) {
      return Types.toString(type);
    }

    boolean jdkTypeDuplicatesOwnerName() {
      return true;
    }
  }

  
Per issue 1635, In JDK 1.7.0_51-b13, TypeVariableImpl.equals(Object) is changed to no longer be equal to custom TypeVariable implementations. As a result, we need to make sure our TypeVariable implementation respects symmetry. Moreover, we don't want to reconstruct a native type variable <A> using our implementation unless some of its bounds have changed in resolution. This avoids creating unequal TypeVariable implementation unnecessarily. When the bounds do change, however, it's fine for the synthetic TypeVariable to be unequal to any native TypeVariable anyway. 
/**
   * Per <a href="https://code.google.com/p/guava-libraries/issues/detail?id=1635">issue 1635</a>,
   * In JDK 1.7.0_51-b13, {@link TypeVariableImpl#equals(Object)} is changed to no longer be equal
   * to custom TypeVariable implementations. As a result, we need to make sure our TypeVariable
   * implementation respects symmetry. Moreover, we don't want to reconstruct a native type variable
   * {@code <A>} using our implementation unless some of its bounds have changed in resolution. This
   * avoids creating unequal TypeVariable implementation unnecessarily. When the bounds do change,
   * however, it's fine for the synthetic TypeVariable to be unequal to any native TypeVariable
   * anyway.
   */
  static final class NativeTypeVariableEquals<X> {
    static final boolean NATIVE_TYPE_VARIABLE_ONLY =
        !NativeTypeVariableEquals.class.getTypeParameters()[0].equals(
            newArtificialTypeVariable(NativeTypeVariableEquals.class, "X"));
  }

  private Types() {}
}