path: root/libjava/classpath/java/util/AbstractCollection.java

/* AbstractCollection.java -- Abstract implementation of most of Collection
   Copyright (C) 1998, 2000, 2001, 2005  Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */


package java.util;

import java.lang.reflect.Array;

/**
 * A basic implementation of most of the methods in the Collection interface to
 * make it easier to create a collection. To create an unmodifiable Collection,
 * just subclass AbstractCollection and provide implementations of the
 * iterator() and size() methods. The Iterator returned by iterator() need only
 * provide implementations of hasNext() and next() (that is, it may throw an
 * UnsupportedOperationException if remove() is called). To create a modifiable
 * Collection, you must in addition provide an implementation of the
 * add(Object) method and the Iterator returned by iterator() must provide an
 * implementation of remove(). Other methods should be overridden if the
 * backing data structure allows for a more efficient implementation. The
 * precise implementation used by AbstractCollection is documented, so that
 * subclasses can tell which methods could be implemented more efficiently.
 * <p>
 *
 * The programmer should provide a no-argument constructor, and one that
 * accepts another Collection, as recommended by the Collection interface.
 * Unfortunately, there is no way to enforce this in Java.
 *
 * @author Original author unknown
 * @author Bryce McKinlay
 * @author Eric Blake (ebb9@email.byu.edu)
 * @see Collection
 * @see AbstractSet
 * @see AbstractList
 * @since 1.2
 * @status updated to 1.4
 */
public abstract class AbstractCollection implements Collection
{
  /**
   * The main constructor, for use by subclasses.
   */
  protected AbstractCollection()
  {
  }

  /**
   * Return an Iterator over this collection. The iterator must provide the
   * hasNext and next methods and should in addition provide remove if the
   * collection is modifiable.
   *
   * @return an iterator
   */
  public abstract Iterator iterator();

  /**
   * Return the number of elements in this collection. If there are more than
   * Integer.MAX_VALUE elements, return Integer.MAX_VALUE.
   *
   * @return the size
   */
  public abstract int size();

  /**
   * Add an object to the collection (optional operation). This implementation
   * always throws an UnsupportedOperationException - it should be
   * overridden if the collection is to be modifiable. If the collection
   * does not accept duplicates, simply return false. Collections may specify
   * limitations on what may be added.
   *
   * @param o the object to add
   * @return true if the add operation caused the Collection to change
   * @throws UnsupportedOperationException if the add operation is not
   *         supported on this collection
   * @throws NullPointerException if the collection does not support null
   * @throws ClassCastException if the object is of the wrong type
   * @throws IllegalArgumentException if some aspect of the object prevents
   *         it from being added
   */
  public boolean add(Object o)
  {
    throw new UnsupportedOperationException();
  }

  /**
   * Add all the elements of a given collection to this collection (optional
   * operation). This implementation obtains an Iterator over the given
   * collection and iterates over it, adding each element with the
   * add(Object) method (thus this method will fail with an
   * UnsupportedOperationException if the add method does). The behavior is
   * unspecified if the specified collection is modified during the iteration,
   * including the special case of trying addAll(this) on a non-empty
   * collection.
   *
   * @param c the collection to add the elements of to this collection
   * @return true if the add operation caused the Collection to change
   * @throws UnsupportedOperationException if the add operation is not
   *         supported on this collection
   * @throws NullPointerException if the specified collection is null
   * @throws ClassCastException if the type of any element in c is
   *         not a valid type for addition.
   * @throws IllegalArgumentException if some aspect of any element
   *         in c prevents it being added.
   * @throws NullPointerException if any element in c is null and this
   *         collection doesn't allow null values.
   * @see #add(Object)
   */
  public boolean addAll(Collection c)
  {
    Iterator itr = c.iterator();
    boolean modified = false;
    int pos = c.size();
    while (--pos >= 0)
      modified |= add(itr.next());
    return modified;
  }

  /**
   * Remove all elements from the collection (optional operation). This
   * implementation obtains an iterator over the collection and calls next
   * and remove on it repeatedly (thus this method will fail with an
   * UnsupportedOperationException if the Iterator's remove method does)
   * until there are no more elements to remove.
   * Many implementations will have a faster way of doing this.
   *
   * @throws UnsupportedOperationException if the Iterator returned by
   *         iterator does not provide an implementation of remove
   * @see Iterator#remove()
   */
  public void clear()
  {
    Iterator itr = iterator();
    int pos = size();
    while (--pos >= 0)
      {
        itr.next();
        itr.remove();
      }
  }

  /**
   * Test whether this collection contains a given object. That is, if the
   * collection has an element e such that (o == null ? e == null :
   * o.equals(e)). This implementation obtains an iterator over the collection
   * and iterates over it, testing each element for equality with the given
   * object. If it is equal, true is returned. Otherwise false is returned when
   * the end of the collection is reached.
   *
   * @param o the object to remove from this collection
   * @return true if this collection contains an object equal to o
   */
  public boolean contains(Object o)
  {
    Iterator itr = iterator();
    int pos = size();
    while (--pos >= 0)
      if (equals(o, itr.next()))
        return true;
    return false;
  }

  /**
   * Tests whether this collection contains all the elements in a given
   * collection. This implementation iterates over the given collection,
   * testing whether each element is contained in this collection. If any one
   * is not, false is returned. Otherwise true is returned.
   *
   * @param c the collection to test against
   * @return true if this collection contains all the elements in the given
   *         collection
   * @throws NullPointerException if the given collection is null
   * @see #contains(Object)
   */
  public boolean containsAll(Collection c)
  {
    Iterator itr = c.iterator();
    int pos = c.size();
    while (--pos >= 0)
      if (!contains(itr.next()))
        return false;
    return true;
  }

  /**
   * Test whether this collection is empty. This implementation returns
   * size() == 0.
   *
   * @return true if this collection is empty.
   * @see #size()
   */
  public boolean isEmpty()
  {
    return size() == 0;
  }

  /**
   * Remove a single instance of an object from this collection (optional
   * operation). That is, remove one element e such that
   * <code>(o == null ? e == null : o.equals(e))</code>, if such an element
   * exists. This implementation obtains an iterator over the collection
   * and iterates over it, testing each element for equality with the given
   * object. If it is equal, it is removed by the iterator's remove method
   * (thus this method will fail with an UnsupportedOperationException if
   * the Iterator's remove method does). After the first element has been
   * removed, true is returned; if the end of the collection is reached, false
   * is returned.
   *
   * @param o the object to remove from this collection
   * @return true if the remove operation caused the Collection to change, or
   *         equivalently if the collection did contain o.
   * @throws UnsupportedOperationException if this collection's Iterator
   *         does not support the remove method
   * @see Iterator#remove()
   */
  public boolean remove(Object o)
  {
    Iterator itr = iterator();
    int pos = size();
    while (--pos >= 0)
      if (equals(o, itr.next()))
        {
          itr.remove();
          return true;
        }
    return false;
  }

  /**
   * Remove from this collection all its elements that are contained in a given
   * collection (optional operation). This implementation iterates over this
   * collection, and for each element tests if it is contained in the given
   * collection. If so, it is removed by the Iterator's remove method (thus
   * this method will fail with an UnsupportedOperationException if the
   * Iterator's remove method does).
   *
   * @param c the collection to remove the elements of
   * @return true if the remove operation caused the Collection to change
   * @throws UnsupportedOperationException if this collection's Iterator
   *         does not support the remove method
   * @throws NullPointerException if the collection, c, is null.
   * @see Iterator#remove()
   */
  public boolean removeAll(Collection c)
  {
    return removeAllInternal(c);
  }

  /**
   * Remove from this collection all its elements that are contained in a given
   * collection (optional operation). This implementation iterates over this
   * collection, and for each element tests if it is contained in the given
   * collection. If so, it is removed by the Iterator's remove method (thus
   * this method will fail with an UnsupportedOperationException if the
   * Iterator's remove method does). This method is necessary for ArrayList,
   * which cannot publicly override removeAll but can optimize this call.
   *
   * @param c the collection to remove the elements of
   * @return true if the remove operation caused the Collection to change
   * @throws UnsupportedOperationException if this collection's Iterator
   *         does not support the remove method
   * @throws NullPointerException if the collection, c, is null.
   * @see Iterator#remove()
   */
  // Package visible for use throughout java.util.
  boolean removeAllInternal(Collection c)
  {
    Iterator itr = iterator();
    boolean modified = false;
    int pos = size();
    while (--pos >= 0)
      if (c.contains(itr.next()))
        {
          itr.remove();
          modified = true;
        }
    return modified;
  }

  /**
   * Remove from this collection all its elements that are not contained in a
   * given collection (optional operation). This implementation iterates over
   * this collection, and for each element tests if it is contained in the
   * given collection. If not, it is removed by the Iterator's remove method
   * (thus this method will fail with an UnsupportedOperationException if
   * the Iterator's remove method does).
   *
   * @param c the collection to retain the elements of
   * @return true if the remove operation caused the Collection to change
   * @throws UnsupportedOperationException if this collection's Iterator
   *         does not support the remove method
   * @throws NullPointerException if the collection, c, is null.
   * @see Iterator#remove()
   */
  public boolean retainAll(Collection c)
  {
    return retainAllInternal(c);
  }

  /**
   * Remove from this collection all its elements that are not contained in a
   * given collection (optional operation). This implementation iterates over
   * this collection, and for each element tests if it is contained in the
   * given collection. If not, it is removed by the Iterator's remove method
   * (thus this method will fail with an UnsupportedOperationException if
   * the Iterator's remove method does). This method is necessary for
   * ArrayList, which cannot publicly override retainAll but can optimize
   * this call.
   *
   * @param c the collection to retain the elements of
   * @return true if the remove operation caused the Collection to change
   * @throws UnsupportedOperationException if this collection's Iterator
   *         does not support the remove method
   * @throws NullPointerException if the collection, c, is null.
   * @see Iterator#remove()
   */
  // Package visible for use throughout java.util.
  boolean retainAllInternal(Collection c)
  {
    Iterator itr = iterator();
    boolean modified = false;
    int pos = size();
    while (--pos >= 0)
      if (!c.contains(itr.next()))
        {
          itr.remove();
          modified = true;
        }
    return modified;
  }

  /**
   * Return an array containing the elements of this collection. This
   * implementation creates an Object array of size size() and then iterates
   * over the collection, setting each element of the array from the value
   * returned by the iterator. The returned array is safe, and is not backed
   * by the collection.
   *
   * @return an array containing the elements of this collection
   */
  public Object[] toArray()
  {
    Iterator itr = iterator();
    int size = size();
    Object[] a = new Object[size];
    for (int pos = 0; pos < size; pos++)
      a[pos] = itr.next();
    return a;
  }

  /**
   * Copy the collection into a given array if it will fit, or into a
   * dynamically created array of the same run-time type as the given array if
   * not. If there is space remaining in the array, the first element after the
   * end of the collection is set to null (this is only useful if the
   * collection is known to contain no null elements, however). This
   * implementation first tests whether the given array is large enough to hold
   * all the elements of the collection. If not, the reflection API is used to
   * allocate a new array of the same run-time type. Next an iterator is
   * obtained over the collection and the elements are placed in the array as
   * they are returned by the iterator. Finally the first spare element, if
   * any, of the array is set to null, and the created array is returned.
   * The returned array is safe; it is not backed by the collection. Note that
   * null may not mark the last element, if the collection allows null
   * elements.
   *
   * @param a the array to copy into, or of the correct run-time type
   * @return the array that was produced
   * @throws NullPointerException if the given array is null
   * @throws ArrayStoreException if the type of the array precludes holding
   *         one of the elements of the Collection
   */
  public Object[] toArray(Object[] a)
  {
    int size = size();
    if (a.length < size)
      a = (Object[]) Array.newInstance(a.getClass().getComponentType(),
                                       size);
    else if (a.length > size)
      a[size] = null;

    Iterator itr = iterator();
    for (int pos = 0; pos < size; pos++)
      a[pos] = itr.next();

    return a;
  }

  /**
   * Creates a String representation of the Collection. The string returned is
   * of the form "[a, b, ...]" where a and b etc are the results of calling
   * toString on the elements of the collection. This implementation obtains an
   * Iterator over the Collection and adds each element to a StringBuffer as it
   * is returned by the iterator.
   *
   * @return a String representation of the Collection
   */
  public String toString()
  {
    Iterator itr = iterator();
    StringBuffer r = new StringBuffer("[");
    for (int pos = size(); pos > 0; pos--)
      {
        r.append(itr.next());
        if (pos > 1)
          r.append(", ");
      }
    r.append("]");
    return r.toString();
  }

  /**
   * Compare two objects according to Collection semantics.
   *
   * @param o1 the first object
   * @param o2 the second object
   * @return o1 == null ? o2 == null : o1.equals(o2)
   */
  // Package visible for use throughout java.util.
  // It may be inlined since it is final.
  static final boolean equals(Object o1, Object o2)
  {
    return o1 == null ? o2 == null : o1.equals(o2);
  }

  /**
   * Hash an object according to Collection semantics.
   *
   * @param o the object to hash
   * @return o1 == null ? 0 : o1.hashCode()
   */
  // Package visible for use throughout java.util.
  // It may be inlined since it is final.
  static final int hashCode(Object o)
  {
    return o == null ? 0 : o.hashCode();
  }
}