core/src/com/google/inject/internal/util/Sets.java

/*
 * Copyright (C) 2007 Google Inc.
 *
 * 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.inject.internal.util;

import com.google.inject.internal.Nullable;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Collections;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

/**
 * Static utility methods pertaining to {@link Set} instances. Also see this
 * class's counterparts {@link Lists} and {@link Maps}.
 *
 * @author Kevin Bourrillion
 * @author Jared Levy
 */
public final class Sets {
  private Sets() {}

  // HashSet

  /**
   * Creates an empty {@code HashSet} instance.
   *
   * <p><b>Note:</b> if {@code E} is an {@link Enum} type, use {@link
   * EnumSet#noneOf} instead.
   *
   * <p><b>Note:</b> if you need an <i>immutable</i> empty Set, use {@link
   * Collections#emptySet} instead.
   *
   * @return a newly created, empty {@code HashSet}
   */
  public static <E> HashSet<E> newHashSet() {
    return new HashSet<E>();
  }

  // TODO: Modify the sets returned by newConcurrentHashSet so calling
  // remove(null) on them doesn't throw an NPE.

  // LinkedHashSet

  /**
   * Creates an empty {@code LinkedHashSet} instance.
   *
   * @return a newly created, empty {@code LinkedHashSet}
   */
  public static <E> LinkedHashSet<E> newLinkedHashSet() {
    return new LinkedHashSet<E>();
  }

  /*
   * Regarding newSetForMap() and SetFromMap:
   *
   * Written by Doug Lea with assistance from members of JCP JSR-166
   * Expert Group and released to the public domain, as explained at
   * http://creativecommons.org/licenses/publicdomain
   */

  /**
   * Returns a set backed by the specified map. The resulting set displays
   * the same ordering, concurrency, and performance characteristics as the
   * backing map. In essence, this factory method provides a {@link Set}
   * implementation corresponding to any {@link Map} implementation. There is no
   * need to use this method on a {@link Map} implementation that already has a
   * corresponding {@link Set} implementation (such as {@link HashMap} or
   * {@link TreeMap}).
   *
   * <p>Each method invocation on the set returned by this method results in
   * exactly one method invocation on the backing map or its <tt>keySet</tt>
   * view, with one exception. The <tt>addAll</tt> method is implemented as a
   * sequence of <tt>put</tt> invocations on the backing map.
   *
   * <p>The specified map must be empty at the time this method is invoked,
   * and should not be accessed directly after this method returns. These
   * conditions are ensured if the map is created empty, passed directly
   * to this method, and no reference to the map is retained, as illustrated
   * in the following code fragment:
   * <pre>
   *    Set&lt;Object&gt; identityHashSet = Sets.newSetFromMap(
   *        new IdentityHashMap&lt;Object, Boolean&gt;()); </pre>
   *
   * This method has the same behavior as the JDK 6 method
   * {@code Collections.newSetFromMap()}. The returned set is serializable if
   * the backing map is.
   *
   * @param map the backing map
   * @return the set backed by the map
   * @throws IllegalArgumentException if <tt>map</tt> is not empty
   */
  public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) {
    return new SetFromMap<E>(map);
  }

  private static class SetFromMap<E> extends AbstractSet<E>
      implements Set<E>, Serializable {
    private final Map<E, Boolean> m; // The backing map
    private transient Set<E> s; // Its keySet

    SetFromMap(Map<E, Boolean> map) {
      Preconditions.checkArgument(map.isEmpty(), "Map is non-empty");
      m = map;
      s = map.keySet();
    }

    @Override public void clear() {
      m.clear();
    }
    @Override public int size() {
      return m.size();
    }
    @Override public boolean isEmpty() {
      return m.isEmpty();
    }
    @Override public boolean contains(Object o) {
      return m.containsKey(o);
    }
    @Override public boolean remove(Object o) {
      return m.remove(o) != null;
    }
    @Override public boolean add(E e) {
      return m.put(e, Boolean.TRUE) == null;
    }
    @Override public Iterator<E> iterator() {
      return s.iterator();
    }
    @Override public Object[] toArray() {
      return s.toArray();
    }
    @Override public <T> T[] toArray(T[] a) {
      return s.toArray(a);
    }
    @Override public String toString() {
      return s.toString();
    }
    @Override public int hashCode() {
      return s.hashCode();
    }
    @Override public boolean equals(@Nullable Object object) {
      return this == object || this.s.equals(object);
    }
    @Override public boolean containsAll(Collection<?> c) {
      return s.containsAll(c);
    }
    @Override public boolean removeAll(Collection<?> c) {
      return s.removeAll(c);
    }
    @Override public boolean retainAll(Collection<?> c) {
      return s.retainAll(c);
    }

    // addAll is the only inherited implementation

    static final long serialVersionUID = 0;

    private void readObject(ObjectInputStream stream)
        throws IOException, ClassNotFoundException {
      stream.defaultReadObject();
      s = m.keySet();
    }
  }

  /**
   * Calculates and returns the hash code of {@code s}.
   */
  static int hashCodeImpl(Set<?> s) {
    int hashCode = 0;
    for (Object o : s) {
      hashCode += o != null ? o.hashCode() : 0;
    }
    return hashCode;
  }
}