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  * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.  Oracle designates this

  * particular file as subject to the "Classpath" exception as provided

  * by Oracle in the LICENSE file that accompanied this code.

  *

  * This code 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

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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  */

 package java.util;

 /**

  * This class provides a skeletal implementation of the <tt>Collection</tt>

  * interface, to minimize the effort required to implement this interface. <p>

  *

  * To implement an unmodifiable collection, the programmer needs only to

  * extend this class and provide implementations for the <tt>iterator</tt> and

  * <tt>size</tt> methods.  (The iterator returned by the <tt>iterator</tt>

  * method must implement <tt>hasNext</tt> and <tt>next</tt>.)<p>

  *

  * To implement a modifiable collection, the programmer must additionally

  * override this class's <tt>add</tt> method (which otherwise throws an

  * <tt>UnsupportedOperationException</tt>), and the iterator returned by the

  * <tt>iterator</tt> method must additionally implement its <tt>remove</tt>

  * method.<p>

  *

  * The programmer should generally provide a void (no argument) and

  * <tt>Collection</tt> constructor, as per the recommendation in the

  * <tt>Collection</tt> interface specification.<p>

  *

  * The documentation for each non-abstract method in this class describes its

  * implementation in detail.  Each of these methods may be overridden if

  * the collection being implemented admits a more efficient implementation.<p>

  *

  * This class is a member of the

  * <a href="{@docRoot}/../technotes/guides/collections/index.html">

  * Java Collections Framework</a>.

  *

  * @author  Josh Bloch

  * @author  Neal Gafter

  * @see Collection

  * @since 1.2

  */

 public abstract class AbstractCollection<E> implements Collection<E> {

     /**

      * Sole constructor.  (For invocation by subclass constructors, typically

      * implicit.)

      */

     protected AbstractCollection() {

     }

     // Query Operations

     /**

      * Returns an iterator over the elements contained in this collection.

      *

      * @return an iterator over the elements contained in this collection

      */

     public abstract Iterator<E> iterator();

     public abstract int size();

     /**

      * {@inheritDoc}

      *

      * <p>This implementation returns <tt>size() == 0</tt>.

      */

     public boolean isEmpty() {

         return size() == 0;

     }

     /**

      * {@inheritDoc}

      *

      * <p>This implementation iterates over the elements in the collection,

      * checking each element in turn for equality with the specified element.

      *

      * @throws ClassCastException   {@inheritDoc}

      * @throws NullPointerException {@inheritDoc}

      */

     public boolean contains(Object o) {

         Iterator<E> it = iterator();

         if (o==null) {

             while (it.hasNext())

                 if (it.next()==null)

                     return true;

         } else {

             while (it.hasNext())

                 if (o.equals(it.next()))

                     return true;

         }

         return false;

     }

     /**

      * {@inheritDoc}

      *

      * <p>This implementation returns an array containing all the elements

      * returned by this collection's iterator, in the same order, stored in

      * consecutive elements of the array, starting with index {@code 0}.

      * The length of the returned array is equal to the number of elements

      * returned by the iterator, even if the size of this collection changes

      * during iteration, as might happen if the collection permits

      * concurrent modification during iteration.  The {@code size} method is

      * called only as an optimization hint; the correct result is returned

      * even if the iterator returns a different number of elements.

      *

      * <p>This method is equivalent to:

      *

      *  <pre> {@code

      * List<E> list = new ArrayList<E>(size());

      * for (E e : this)

      *     list.add(e);

      * return list.toArray();

      * }</pre>

      */

     public Object[] toArray() {

         // Estimate size of array; be prepared to see more or fewer elements

         Object[] r = new Object[size()];

         Iterator<E> it = iterator();

         for (int i = 0; i < r.length; i++) {

             if (! it.hasNext()) // fewer elements than expected

                 return Arrays.copyOf(r, i);

             r[i] = it.next();

         }

         return it.hasNext() ? finishToArray(r, it) : r;

     }

     /**

      * {@inheritDoc}

      *

      * <p>This implementation returns an array containing all the elements

      * returned by this collection's iterator in the same order, stored in

      * consecutive elements of the array, starting with index {@code 0}.

      * If the number of elements returned by the iterator is too large to

      * fit into the specified array, then the elements are returned in a

      * newly allocated array with length equal to the number of elements

      * returned by the iterator, even if the size of this collection

      * changes during iteration, as might happen if the collection permits

      * concurrent modification during iteration.  The {@code size} method is

      * called only as an optimization hint; the correct result is returned

      * even if the iterator returns a different number of elements.

      *

      * <p>This method is equivalent to:

      *

      *  <pre> {@code

      * List<E> list = new ArrayList<E>(size());

      * for (E e : this)

      *     list.add(e);

      * return list.toArray(a);

      * }</pre>

      *

      * @throws ArrayStoreException  {@inheritDoc}

      * @throws NullPointerException {@inheritDoc}

      */

     public <T> T[] toArray(T[] a) {

         // Estimate size of array; be prepared to see more or fewer elements

         int size = size();

         T[] r = a.length >= size ? a :

                   (T[])java.lang.reflect.Array

                   .newInstance(a.getClass().getComponentType(), size);

         Iterator<E> it = iterator();

         for (int i = 0; i < r.length; i++) {

             if (! it.hasNext()) { // fewer elements than expected

                 if (a != r)

                     return Arrays.copyOf(r, i);

                 r[i] = null; // null-terminate

                 return r;

             }

             r[i] = (T)it.next();

         }

         return it.hasNext() ? finishToArray(r, it) : r;

     }

     /**

      * The maximum size of array to allocate.

      * Some VMs reserve some header words in an array.

      * Attempts to allocate larger arrays may result in

      * OutOfMemoryError: Requested array size exceeds VM limit

      */

     private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;

     /**

      * Reallocates the array being used within toArray when the iterator

      * returned more elements than expected, and finishes filling it from

      * the iterator.

      *

      * @param r the array, replete with previously stored elements

      * @param it the in-progress iterator over this collection

      * @return array containing the elements in the given array, plus any

      *         further elements returned by the iterator, trimmed to size

      */

     private static <T> T[] finishToArray(T[] r, Iterator<?> it) {

         int i = r.length;

         while (it.hasNext()) {

             int cap = r.length;

             if (i == cap) {

                 int newCap = cap + (cap >> 1) + 1;

                 // overflow-conscious code

                 if (newCap - MAX_ARRAY_SIZE > 0)

                     newCap = hugeCapacity(cap + 1);

                 r = Arrays.copyOf(r, newCap);

             }

             r[i++] = (T)it.next();

         }

         // trim if overallocated

         return (i == r.length) ? r : Arrays.copyOf(r, i);

     }

     private static int hugeCapacity(int minCapacity) {

         if (minCapacity < 0) // overflow

             throw new OutOfMemoryError

                 ("Required array size too large");

         return (minCapacity > MAX_ARRAY_SIZE) ?

             Integer.MAX_VALUE :

             MAX_ARRAY_SIZE;

     }

     // Modification Operations

     /**

      * {@inheritDoc}

      *

      * <p>This implementation always throws an

      * <tt>UnsupportedOperationException</tt>.

      *

      * @throws UnsupportedOperationException {@inheritDoc}

      * @throws ClassCastException            {@inheritDoc}

      * @throws NullPointerException          {@inheritDoc}

      * @throws IllegalArgumentException      {@inheritDoc}

      * @throws IllegalStateException         {@inheritDoc}

      */

     public boolean add(E e) {

         throw new UnsupportedOperationException();

     }

     /**

      * {@inheritDoc}

      *

      * <p>This implementation iterates over the collection looking for the

      * specified element.  If it finds the element, it removes the element

      * from the collection using the iterator's remove method.

      *

      * <p>Note that this implementation throws an

      * <tt>UnsupportedOperationException</tt> if the iterator returned by this

      * collection's iterator method does not implement the <tt>remove</tt>

      * method and this collection contains the specified object.

      *

      * @throws UnsupportedOperationException {@inheritDoc}

      * @throws ClassCastException            {@inheritDoc}

      * @throws NullPointerException          {@inheritDoc}

      */

     public boolean remove(Object o) {

         Iterator<E> it = iterator();

         if (o==null) {

             while (it.hasNext()) {

                 if (it.next()==null) {

                     it.remove();

                     return true;

                 }

             }

         } else {

             while (it.hasNext()) {

                 if (o.equals(it.next())) {

                     it.remove();

                     return true;

                 }

             }

         }

         return false;

     }

     // Bulk Operations

     /**

      * {@inheritDoc}

      *

      * <p>This implementation iterates over the specified collection,

      * checking each element returned by the iterator in turn to see

      * if it's contained in this collection.  If all elements are so

      * contained <tt>true</tt> is returned, otherwise <tt>false</tt>.

      *

      * @throws ClassCastException            {@inheritDoc}

      * @throws NullPointerException          {@inheritDoc}

      * @see #contains(Object)

      */

     public boolean containsAll(Collection<?> c) {

         for (Object e : c)

             if (!contains(e))

                 return false;

         return true;

     }

     /**

      * {@inheritDoc}

      *

      * <p>This implementation iterates over the specified collection, and adds

      * each object returned by the iterator to this collection, in turn.

      *

      * <p>Note that this implementation will throw an

      * <tt>UnsupportedOperationException</tt> unless <tt>add</tt> is

      * overridden (assuming the specified collection is non-empty).

      *

      * @throws UnsupportedOperationException {@inheritDoc}

      * @throws ClassCastException            {@inheritDoc}

      * @throws NullPointerException          {@inheritDoc}

      * @throws IllegalArgumentException      {@inheritDoc}

      * @throws IllegalStateException         {@inheritDoc}

      *

      * @see #add(Object)

      */

     public boolean addAll(Collection<? extends E> c) {

         boolean modified = false;

         for (E e : c)

             if (add(e))

                 modified = true;

         return modified;

     }

     /**

      * {@inheritDoc}

      *

      * <p>This implementation iterates over this collection, checking each

      * element returned by the iterator in turn to see if it's contained

      * in the specified collection.  If it's so contained, it's removed from

      * this collection with the iterator's <tt>remove</tt> method.

      *

      * <p>Note that this implementation will throw an

      * <tt>UnsupportedOperationException</tt> if the iterator returned by the

      * <tt>iterator</tt> method does not implement the <tt>remove</tt> method

      * and this collection contains one or more elements in common with the

      * specified collection.

      *

      * @throws UnsupportedOperationException {@inheritDoc}

      * @throws ClassCastException            {@inheritDoc}

      * @throws NullPointerException          {@inheritDoc}

      *

      * @see #remove(Object)

      * @see #contains(Object)

      */

     public boolean removeAll(Collection<?> c) {

         boolean modified = false;

         Iterator<?> it = iterator();

         while (it.hasNext()) {

             if (c.contains(it.next())) {

                 it.remove();

                 modified = true;

             }

         }

         return modified;

     }

     /**

      * {@inheritDoc}

      *

      * <p>This implementation iterates over this collection, checking each

      * element returned by the iterator in turn to see if it's contained

      * in the specified collection.  If it's not so contained, it's removed

      * from this collection with the iterator's <tt>remove</tt> method.

      *

      * <p>Note that this implementation will throw an

      * <tt>UnsupportedOperationException</tt> if the iterator returned by the

      * <tt>iterator</tt> method does not implement the <tt>remove</tt> method

      * and this collection contains one or more elements not present in the

      * specified collection.

      *

      * @throws UnsupportedOperationException {@inheritDoc}

      * @throws ClassCastException            {@inheritDoc}

      * @throws NullPointerException          {@inheritDoc}

      *

      * @see #remove(Object)

      * @see #contains(Object)

      */

     public boolean retainAll(Collection<?> c) {

         boolean modified = false;

         Iterator<E> it = iterator();

         while (it.hasNext()) {

             if (!c.contains(it.next())) {

                 it.remove();

                 modified = true;

             }

         }

         return modified;

     }

     /**

      * {@inheritDoc}

      *

      * <p>This implementation iterates over this collection, removing each

      * element using the <tt>Iterator.remove</tt> operation.  Most

      * implementations will probably choose to override this method for

      * efficiency.

      *

      * <p>Note that this implementation will throw an

      * <tt>UnsupportedOperationException</tt> if the iterator returned by this

      * collection's <tt>iterator</tt> method does not implement the

      * <tt>remove</tt> method and this collection is non-empty.

      *

      * @throws UnsupportedOperationException {@inheritDoc}

      */

     public void clear() {

         Iterator<E> it = iterator();

         while (it.hasNext()) {

             it.next();

             it.remove();

         }

     }

     //  String conversion

     /**

      * Returns a string representation of this collection.  The string

      * representation consists of a list of the collection's elements in the

      * order they are returned by its iterator, enclosed in square brackets

      * (<tt>"[]"</tt>).  Adjacent elements are separated by the characters

      * <tt>", "</tt> (comma and space).  Elements are converted to strings as

      * by {@link String#valueOf(Object)}.

      *

      * @return a string representation of this collection

      */

     public String toString() {

         Iterator<E> it = iterator();

         if (! it.hasNext())

             return "[]";

         StringBuilder sb = new StringBuilder();

         sb.append('[');

         for (;;) {

             E e = it.next();

             sb.append(e == this ? "(this Collection)" : e);

             if (! it.hasNext())

                 return sb.append(']').toString();

             sb.append(',').append(' ');

         }

     }

 }