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) 2007 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.base;

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

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;
import java.util.regex.Pattern;
import org.checkerframework.checker.nullness.qual.Nullable;


Static utility methods pertaining to Predicate instances. 
All methods return serializable predicates as long as they're given serializable parameters.

See the Guava User Guide article on the use of Predicate.

Author:Kevin Bourrillion
Since:2.0
/**
 * Static utility methods pertaining to {@code Predicate} instances.
 *
 * <p>All methods return serializable predicates as long as they're given serializable parameters.
 *
 * <p>See the Guava User Guide article on <a
 * href="https://github.com/google/guava/wiki/FunctionalExplained">the use of {@code Predicate}</a>.
 *
 * @author Kevin Bourrillion
 * @since 2.0
 */
@GwtCompatible(emulated = true)
public final class Predicates {
  private Predicates() {}

  // TODO(kevinb): considering having these implement a VisitablePredicate
  // interface which specifies an accept(PredicateVisitor) method.

  
Returns a predicate that always evaluates to true. 
/** Returns a predicate that always evaluates to {@code true}. */
  @GwtCompatible(serializable = true)
  public static <T> Predicate<T> alwaysTrue() {
    return ObjectPredicate.ALWAYS_TRUE.withNarrowedType();
  }

  
Returns a predicate that always evaluates to false. 
/** Returns a predicate that always evaluates to {@code false}. */
  @GwtCompatible(serializable = true)
  public static <T> Predicate<T> alwaysFalse() {
    return ObjectPredicate.ALWAYS_FALSE.withNarrowedType();
  }

  
Returns a predicate that evaluates to true if the object reference being tested is null. 
/**
   * Returns a predicate that evaluates to {@code true} if the object reference being tested is
   * null.
   */
  @GwtCompatible(serializable = true)
  public static <T> Predicate<T> isNull() {
    return ObjectPredicate.IS_NULL.withNarrowedType();
  }

  
Returns a predicate that evaluates to true if the object reference being tested is not null. 
/**
   * Returns a predicate that evaluates to {@code true} if the object reference being tested is not
   * null.
   */
  @GwtCompatible(serializable = true)
  public static <T> Predicate<T> notNull() {
    return ObjectPredicate.NOT_NULL.withNarrowedType();
  }

  
Returns a predicate that evaluates to true if the given predicate evaluates to 
false. 
/**
   * Returns a predicate that evaluates to {@code true} if the given predicate evaluates to {@code
   * false}.
   */
  public static <T> Predicate<T> not(Predicate<T> predicate) {
    return new NotPredicate<T>(predicate);
  }

  
Returns a predicate that evaluates to true if each of its components evaluates to true. The components are evaluated in order, and evaluation will be "short-circuited" as soon as a false predicate is found. It defensively copies the iterable passed in, so future changes to it won't alter the behavior of this predicate. If components is empty, the returned predicate will always evaluate to true. 
/**
   * Returns a predicate that evaluates to {@code true} if each of its components evaluates to
   * {@code true}. The components are evaluated in order, and evaluation will be "short-circuited"
   * as soon as a false predicate is found. It defensively copies the iterable passed in, so future
   * changes to it won't alter the behavior of this predicate. If {@code components} is empty, the
   * returned predicate will always evaluate to {@code true}.
   */
  public static <T> Predicate<T> and(Iterable<? extends Predicate<? super T>> components) {
    return new AndPredicate<T>(defensiveCopy(components));
  }

  
Returns a predicate that evaluates to true if each of its components evaluates to true. The components are evaluated in order, and evaluation will be "short-circuited" as soon as a false predicate is found. It defensively copies the array passed in, so future changes to it won't alter the behavior of this predicate. If components is empty, the returned predicate will always evaluate to true. 
/**
   * Returns a predicate that evaluates to {@code true} if each of its components evaluates to
   * {@code true}. The components are evaluated in order, and evaluation will be "short-circuited"
   * as soon as a false predicate is found. It defensively copies the array passed in, so future
   * changes to it won't alter the behavior of this predicate. If {@code components} is empty, the
   * returned predicate will always evaluate to {@code true}.
   */
  @SafeVarargs
  public static <T> Predicate<T> and(Predicate<? super T>... components) {
    return new AndPredicate<T>(defensiveCopy(components));
  }

  
Returns a predicate that evaluates to true if both of its components evaluate to 
true. The components are evaluated in order, and evaluation will be "short-circuited" as soon as a false predicate is found. 
/**
   * Returns a predicate that evaluates to {@code true} if both of its components evaluate to {@code
   * true}. The components are evaluated in order, and evaluation will be "short-circuited" as soon
   * as a false predicate is found.
   */
  public static <T> Predicate<T> and(Predicate<? super T> first, Predicate<? super T> second) {
    return new AndPredicate<T>(Predicates.<T>asList(checkNotNull(first), checkNotNull(second)));
  }

  
Returns a predicate that evaluates to true if any one of its components evaluates to true. The components are evaluated in order, and evaluation will be "short-circuited" as soon as a true predicate is found. It defensively copies the iterable passed in, so future changes to it won't alter the behavior of this predicate. If components is empty, the returned predicate will always evaluate to false. 
/**
   * Returns a predicate that evaluates to {@code true} if any one of its components evaluates to
   * {@code true}. The components are evaluated in order, and evaluation will be "short-circuited"
   * as soon as a true predicate is found. It defensively copies the iterable passed in, so future
   * changes to it won't alter the behavior of this predicate. If {@code components} is empty, the
   * returned predicate will always evaluate to {@code false}.
   */
  public static <T> Predicate<T> or(Iterable<? extends Predicate<? super T>> components) {
    return new OrPredicate<T>(defensiveCopy(components));
  }

  
Returns a predicate that evaluates to true if any one of its components evaluates to true. The components are evaluated in order, and evaluation will be "short-circuited" as soon as a true predicate is found. It defensively copies the array passed in, so future changes to it won't alter the behavior of this predicate. If components is empty, the returned predicate will always evaluate to false. 
/**
   * Returns a predicate that evaluates to {@code true} if any one of its components evaluates to
   * {@code true}. The components are evaluated in order, and evaluation will be "short-circuited"
   * as soon as a true predicate is found. It defensively copies the array passed in, so future
   * changes to it won't alter the behavior of this predicate. If {@code components} is empty, the
   * returned predicate will always evaluate to {@code false}.
   */
  @SafeVarargs
  public static <T> Predicate<T> or(Predicate<? super T>... components) {
    return new OrPredicate<T>(defensiveCopy(components));
  }

  
Returns a predicate that evaluates to true if either of its components evaluates to true. The components are evaluated in order, and evaluation will be "short-circuited" as soon as a true predicate is found. 
/**
   * Returns a predicate that evaluates to {@code true} if either of its components evaluates to
   * {@code true}. The components are evaluated in order, and evaluation will be "short-circuited"
   * as soon as a true predicate is found.
   */
  public static <T> Predicate<T> or(Predicate<? super T> first, Predicate<? super T> second) {
    return new OrPredicate<T>(Predicates.<T>asList(checkNotNull(first), checkNotNull(second)));
  }

  
Returns a predicate that evaluates to true if the object being tested equals() the given target or both are null. 
/**
   * Returns a predicate that evaluates to {@code true} if the object being tested {@code equals()}
   * the given target or both are null.
   */
  public static <T> Predicate<T> equalTo(@Nullable T target) {
    return (target == null) ? Predicates.<T>isNull() : new IsEqualToPredicate<T>(target);
  }

  
Returns a predicate that evaluates to true if the object being tested is an instance of the given class. If the object being tested is null this predicate evaluates to 
false. 
If you want to filter an Iterable to narrow its type, consider using Iterables.filter(Iterable<?>, Class<Object>) in preference. 
Warning: contrary to the typical assumptions about predicates (as documented at Predicate.apply), the returned predicate may not be consistent with equals. For example, instanceOf(ArrayList.class) will yield different results for the two equal instances Lists.newArrayList(1) and Arrays.asList(1). 
/**
   * Returns a predicate that evaluates to {@code true} if the object being tested is an instance of
   * the given class. If the object being tested is {@code null} this predicate evaluates to {@code
   * false}.
   *
   * <p>If you want to filter an {@code Iterable} to narrow its type, consider using {@link
   * com.google.common.collect.Iterables#filter(Iterable, Class)} in preference.
   *
   * <p><b>Warning:</b> contrary to the typical assumptions about predicates (as documented at
   * {@link Predicate#apply}), the returned predicate may not be <i>consistent with equals</i>. For
   * example, {@code instanceOf(ArrayList.class)} will yield different results for the two equal
   * instances {@code Lists.newArrayList(1)} and {@code Arrays.asList(1)}.
   */
  @GwtIncompatible // Class.isInstance
  public static Predicate<Object> instanceOf(Class<?> clazz) {
    return new InstanceOfPredicate(clazz);
  }

  
Returns a predicate that evaluates to true if the class being tested is assignable to (is a subtype of) clazz. Example: 

List<Class<?>> classes = Arrays.asList(
    Object.class, String.class, Number.class, Long.class);
return Iterables.filter(classes, subtypeOf(Number.class));

 The code above returns an iterable containing Number.class and Long.class. 
Since:20.0 (since 10.0 under the incorrect name assignableFrom)
/**
   * Returns a predicate that evaluates to {@code true} if the class being tested is assignable to
   * (is a subtype of) {@code clazz}. Example:
   *
   * <pre>{@code
   * List<Class<?>> classes = Arrays.asList(
   *     Object.class, String.class, Number.class, Long.class);
   * return Iterables.filter(classes, subtypeOf(Number.class));
   * }</pre>
   *
   * The code above returns an iterable containing {@code Number.class} and {@code Long.class}.
   *
   * @since 20.0 (since 10.0 under the incorrect name {@code assignableFrom})
   */
  @GwtIncompatible // Class.isAssignableFrom
  @Beta
  public static Predicate<Class<?>> subtypeOf(Class<?> clazz) {
    return new SubtypeOfPredicate(clazz);
  }

  
Returns a predicate that evaluates to true if the object reference being tested is a member of the given collection. It does not defensively copy the collection passed in, so future changes to it will alter the behavior of the predicate. 
This method can technically accept any Collection<?>, but using a typed collection helps prevent bugs. This approach doesn't block any potential users since it is always possible to use Predicates.<Object>in(). 
Params:
  • target – the collection that may contain the function input
/**
   * Returns a predicate that evaluates to {@code true} if the object reference being tested is a
   * member of the given collection. It does not defensively copy the collection passed in, so
   * future changes to it will alter the behavior of the predicate.
   *
   * <p>This method can technically accept any {@code Collection<?>}, but using a typed collection
   * helps prevent bugs. This approach doesn't block any potential users since it is always possible
   * to use {@code Predicates.<Object>in()}.
   *
   * @param target the collection that may contain the function input
   */
  public static <T> Predicate<T> in(Collection<? extends T> target) {
    return new InPredicate<T>(target);
  }

  
Returns the composition of a function and a predicate. For every x, the generated predicate returns predicate(function(x)). 
Returns:the composition of the provided function and predicate
/**
   * Returns the composition of a function and a predicate. For every {@code x}, the generated
   * predicate returns {@code predicate(function(x))}.
   *
   * @return the composition of the provided function and predicate
   */
  public static <A, B> Predicate<A> compose(
      Predicate<B> predicate, Function<A, ? extends B> function) {
    return new CompositionPredicate<>(predicate, function);
  }

  
Returns a predicate that evaluates to true if the CharSequence being tested contains any match for the given regular expression pattern. The test used is equivalent to Pattern.compile(pattern).matcher(arg).find() 
Throws:
Since:3.0
/**
   * Returns a predicate that evaluates to {@code true} if the {@code CharSequence} being tested
   * contains any match for the given regular expression pattern. The test used is equivalent to
   * {@code Pattern.compile(pattern).matcher(arg).find()}
   *
   * @throws IllegalArgumentException if the pattern is invalid
   * @since 3.0
   */
  @GwtIncompatible // Only used by other GWT-incompatible code.
  public static Predicate<CharSequence> containsPattern(String pattern) {
    return new ContainsPatternFromStringPredicate(pattern);
  }

  
Returns a predicate that evaluates to true if the CharSequence being tested contains any match for the given regular expression pattern. The test used is equivalent to pattern.matcher(arg).find() 
Since:3.0
/**
   * Returns a predicate that evaluates to {@code true} if the {@code CharSequence} being tested
   * contains any match for the given regular expression pattern. The test used is equivalent to
   * {@code pattern.matcher(arg).find()}
   *
   * @since 3.0
   */
  @GwtIncompatible(value = "java.util.regex.Pattern")
  public static Predicate<CharSequence> contains(Pattern pattern) {
    return new ContainsPatternPredicate(new JdkPattern(pattern));
  }

  // End public API, begin private implementation classes.

  // Package private for GWT serialization.
  enum ObjectPredicate implements Predicate<Object> {
    
See Also:
/** @see Predicates#alwaysTrue() */
    ALWAYS_TRUE {
      @Override
      public boolean apply(@Nullable Object o) {
        return true;
      }

      @Override
      public String toString() {
        return "Predicates.alwaysTrue()";
      }
    },
    
See Also:
/** @see Predicates#alwaysFalse() */
    ALWAYS_FALSE {
      @Override
      public boolean apply(@Nullable Object o) {
        return false;
      }

      @Override
      public String toString() {
        return "Predicates.alwaysFalse()";
      }
    },
    
See Also:
/** @see Predicates#isNull() */
    IS_NULL {
      @Override
      public boolean apply(@Nullable Object o) {
        return o == null;
      }

      @Override
      public String toString() {
        return "Predicates.isNull()";
      }
    },
    
See Also:
/** @see Predicates#notNull() */
    NOT_NULL {
      @Override
      public boolean apply(@Nullable Object o) {
        return o != null;
      }

      @Override
      public String toString() {
        return "Predicates.notNull()";
      }
    };

    @SuppressWarnings("unchecked") // safe contravariant cast
    <T> Predicate<T> withNarrowedType() {
      return (Predicate<T>) this;
    }
  }

  
See Also:
/** @see Predicates#not(Predicate) */
  private static class NotPredicate<T> implements Predicate<T>, Serializable {
    final Predicate<T> predicate;

    NotPredicate(Predicate<T> predicate) {
      this.predicate = checkNotNull(predicate);
    }

    @Override
    public boolean apply(@Nullable T t) {
      return !predicate.apply(t);
    }

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

    @Override
    public boolean equals(@Nullable Object obj) {
      if (obj instanceof NotPredicate) {
        NotPredicate<?> that = (NotPredicate<?>) obj;
        return predicate.equals(that.predicate);
      }
      return false;
    }

    @Override
    public String toString() {
      return "Predicates.not(" + predicate + ")";
    }

    private static final long serialVersionUID = 0;
  }

  
See Also:
/** @see Predicates#and(Iterable) */
  private static class AndPredicate<T> implements Predicate<T>, Serializable {
    private final List<? extends Predicate<? super T>> components;

    private AndPredicate(List<? extends Predicate<? super T>> components) {
      this.components = components;
    }

    @Override
    public boolean apply(@Nullable T t) {
      // Avoid using the Iterator to avoid generating garbage (issue 820).
      for (int i = 0; i < components.size(); i++) {
        if (!components.get(i).apply(t)) {
          return false;
        }
      }
      return true;
    }

    @Override
    public int hashCode() {
      // add a random number to avoid collisions with OrPredicate
      return components.hashCode() + 0x12472c2c;
    }

    @Override
    public boolean equals(@Nullable Object obj) {
      if (obj instanceof AndPredicate) {
        AndPredicate<?> that = (AndPredicate<?>) obj;
        return components.equals(that.components);
      }
      return false;
    }

    @Override
    public String toString() {
      return toStringHelper("and", components);
    }

    private static final long serialVersionUID = 0;
  }

  
See Also:
/** @see Predicates#or(Iterable) */
  private static class OrPredicate<T> implements Predicate<T>, Serializable {
    private final List<? extends Predicate<? super T>> components;

    private OrPredicate(List<? extends Predicate<? super T>> components) {
      this.components = components;
    }

    @Override
    public boolean apply(@Nullable T t) {
      // Avoid using the Iterator to avoid generating garbage (issue 820).
      for (int i = 0; i < components.size(); i++) {
        if (components.get(i).apply(t)) {
          return true;
        }
      }
      return false;
    }

    @Override
    public int hashCode() {
      // add a random number to avoid collisions with AndPredicate
      return components.hashCode() + 0x053c91cf;
    }

    @Override
    public boolean equals(@Nullable Object obj) {
      if (obj instanceof OrPredicate) {
        OrPredicate<?> that = (OrPredicate<?>) obj;
        return components.equals(that.components);
      }
      return false;
    }

    @Override
    public String toString() {
      return toStringHelper("or", components);
    }

    private static final long serialVersionUID = 0;
  }

  private static String toStringHelper(String methodName, Iterable<?> components) {
    StringBuilder builder = new StringBuilder("Predicates.").append(methodName).append('(');
    boolean first = true;
    for (Object o : components) {
      if (!first) {
        builder.append(',');
      }
      builder.append(o);
      first = false;
    }
    return builder.append(')').toString();
  }

  
See Also:
/** @see Predicates#equalTo(Object) */
  private static class IsEqualToPredicate<T> implements Predicate<T>, Serializable {
    private final T target;

    private IsEqualToPredicate(T target) {
      this.target = target;
    }

    @Override
    public boolean apply(T t) {
      return target.equals(t);
    }

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

    @Override
    public boolean equals(@Nullable Object obj) {
      if (obj instanceof IsEqualToPredicate) {
        IsEqualToPredicate<?> that = (IsEqualToPredicate<?>) obj;
        return target.equals(that.target);
      }
      return false;
    }

    @Override
    public String toString() {
      return "Predicates.equalTo(" + target + ")";
    }

    private static final long serialVersionUID = 0;
  }

  
See Also:
/** @see Predicates#instanceOf(Class) */
  @GwtIncompatible // Class.isInstance
  private static class InstanceOfPredicate implements Predicate<Object>, Serializable {
    private final Class<?> clazz;

    private InstanceOfPredicate(Class<?> clazz) {
      this.clazz = checkNotNull(clazz);
    }

    @Override
    public boolean apply(@Nullable Object o) {
      return clazz.isInstance(o);
    }

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

    @Override
    public boolean equals(@Nullable Object obj) {
      if (obj instanceof InstanceOfPredicate) {
        InstanceOfPredicate that = (InstanceOfPredicate) obj;
        return clazz == that.clazz;
      }
      return false;
    }

    @Override
    public String toString() {
      return "Predicates.instanceOf(" + clazz.getName() + ")";
    }

    private static final long serialVersionUID = 0;
  }

  
See Also:
/** @see Predicates#subtypeOf(Class) */
  @GwtIncompatible // Class.isAssignableFrom
  private static class SubtypeOfPredicate implements Predicate<Class<?>>, Serializable {
    private final Class<?> clazz;

    private SubtypeOfPredicate(Class<?> clazz) {
      this.clazz = checkNotNull(clazz);
    }

    @Override
    public boolean apply(Class<?> input) {
      return clazz.isAssignableFrom(input);
    }

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

    @Override
    public boolean equals(@Nullable Object obj) {
      if (obj instanceof SubtypeOfPredicate) {
        SubtypeOfPredicate that = (SubtypeOfPredicate) obj;
        return clazz == that.clazz;
      }
      return false;
    }

    @Override
    public String toString() {
      return "Predicates.subtypeOf(" + clazz.getName() + ")";
    }

    private static final long serialVersionUID = 0;
  }

  
See Also:
/** @see Predicates#in(Collection) */
  private static class InPredicate<T> implements Predicate<T>, Serializable {
    private final Collection<?> target;

    private InPredicate(Collection<?> target) {
      this.target = checkNotNull(target);
    }

    @Override
    public boolean apply(@Nullable T t) {
      try {
        return target.contains(t);
      } catch (NullPointerException | ClassCastException e) {
        return false;
      }
    }

    @Override
    public boolean equals(@Nullable Object obj) {
      if (obj instanceof InPredicate) {
        InPredicate<?> that = (InPredicate<?>) obj;
        return target.equals(that.target);
      }
      return false;
    }

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

    @Override
    public String toString() {
      return "Predicates.in(" + target + ")";
    }

    private static final long serialVersionUID = 0;
  }

  
See Also:
/** @see Predicates#compose(Predicate, Function) */
  private static class CompositionPredicate<A, B> implements Predicate<A>, Serializable {
    final Predicate<B> p;
    final Function<A, ? extends B> f;

    private CompositionPredicate(Predicate<B> p, Function<A, ? extends B> f) {
      this.p = checkNotNull(p);
      this.f = checkNotNull(f);
    }

    @Override
    public boolean apply(@Nullable A a) {
      return p.apply(f.apply(a));
    }

    @Override
    public boolean equals(@Nullable Object obj) {
      if (obj instanceof CompositionPredicate) {
        CompositionPredicate<?, ?> that = (CompositionPredicate<?, ?>) obj;
        return f.equals(that.f) && p.equals(that.p);
      }
      return false;
    }

    @Override
    public int hashCode() {
      return f.hashCode() ^ p.hashCode();
    }

    @Override
    public String toString() {
      // TODO(cpovirk): maybe make this look like the method call does ("Predicates.compose(...)")
      return p + "(" + f + ")";
    }

    private static final long serialVersionUID = 0;
  }

  
See Also:
/** @see Predicates#contains(Pattern) */
  @GwtIncompatible // Only used by other GWT-incompatible code.
  private static class ContainsPatternPredicate implements Predicate<CharSequence>, Serializable {
    final CommonPattern pattern;

    ContainsPatternPredicate(CommonPattern pattern) {
      this.pattern = checkNotNull(pattern);
    }

    @Override
    public boolean apply(CharSequence t) {
      return pattern.matcher(t).find();
    }

    @Override
    public int hashCode() {
      // Pattern uses Object.hashCode, so we have to reach
      // inside to build a hashCode consistent with equals.

      return Objects.hashCode(pattern.pattern(), pattern.flags());
    }

    @Override
    public boolean equals(@Nullable Object obj) {
      if (obj instanceof ContainsPatternPredicate) {
        ContainsPatternPredicate that = (ContainsPatternPredicate) obj;

        // Pattern uses Object (identity) equality, so we have to reach
        // inside to compare individual fields.
        return Objects.equal(pattern.pattern(), that.pattern.pattern())
            && pattern.flags() == that.pattern.flags();
      }
      return false;
    }

    @Override
    public String toString() {
      String patternString =
          MoreObjects.toStringHelper(pattern)
              .add("pattern", pattern.pattern())
              .add("pattern.flags", pattern.flags())
              .toString();
      return "Predicates.contains(" + patternString + ")";
    }

    private static final long serialVersionUID = 0;
  }

  
See Also:
/** @see Predicates#containsPattern(String) */
  @GwtIncompatible // Only used by other GWT-incompatible code.
  private static class ContainsPatternFromStringPredicate extends ContainsPatternPredicate {

    ContainsPatternFromStringPredicate(String string) {
      super(Platform.compilePattern(string));
    }

    @Override
    public String toString() {
      return "Predicates.containsPattern(" + pattern.pattern() + ")";
    }

    private static final long serialVersionUID = 0;
  }

  private static <T> List<Predicate<? super T>> asList(
      Predicate<? super T> first, Predicate<? super T> second) {
    // TODO(kevinb): understand why we still get a warning despite @SafeVarargs!
    return Arrays.<Predicate<? super T>>asList(first, second);
  }

  private static <T> List<T> defensiveCopy(T... array) {
    return defensiveCopy(Arrays.asList(array));
  }

  static <T> List<T> defensiveCopy(Iterable<T> iterable) {
    ArrayList<T> list = new ArrayList<T>();
    for (T element : iterable) {
      list.add(checkNotNull(element));
    }
    return list;
  }
}