java/util/AbstractCollection.java

/*
 * %W% %E%
 *
 * Copyright 2005 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

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 methods 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}/../guide/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @author  Josh Bloch
 * @author  Neal Gafter
 * @version 1.24, 01/18/03
 * @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> e = iterator();
        if (o==null) {
            while (e.hasNext())
                if (e.next()==null)
                    return true;
        } else {
            while (e.hasNext())
                if (o.equals(e.next()))
                    return true;
        }
        return false;
    }

    /**
     * {@inheritDoc}
     *
     * <p>This implementation allocates the array to be returned, and iterates
     * over the elements in the collection, storing each object reference in
     * the next consecutive element of the array, starting with element 0.
     */
    public Object[] toArray() {
        // Estimate size of array; be prepared to see more or fewer elements
        Object[] r = new Object[size()];
        int i = 0;
        Iterator<E> it = iterator();
        while (i < r.length && it.hasNext())
            r[i++] = it.next();
        // Trim if overallocated; expand if underallocated
        if (i < r.length || it.hasNext())
            return resizeAndFinishToArray(r, i, it);
        return r;
    }

    /**
     * {@inheritDoc}
     *
     * <p>This implementation checks if the array is large enough to contain the
     * collection; if not, it allocates a new array of the correct size and
     * type (using reflection).  Then, it iterates over the collection,
     * storing each object reference in the next consecutive element of the
     * array, starting with element 0.  If the array is larger than the
     * collection, a <tt>null</tt> is stored in the first location after the
     * end of the collection.
     *
     * @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);
        int i = 0;
        Iterator<E> it = iterator();
        while (i < r.length && it.hasNext())
            r[i++] = (T)it.next();
        // Trim if overallocated; expand if underallocated
        if (it.hasNext() || (r != a && i < r.length))
            return resizeAndFinishToArray(r, i, it);
        if (i < r.length)
            r[i] = null; // null-terminate if provided array is too big
        return r;
    }

    /**
     * Reallocates the array being used within toArray that has a
     * different number of elements than expected, and finishes
     * filling it from the given iterator, if necessary.
     *
     * @param r the array
     * @param i the next array index to fill
     * @param it the in-progress iterator over the 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[] resizeAndFinishToArray(T[] r, int i, Iterator<?> it) {
        while (it.hasNext()) {
            int cap = r.length;
            if (i < cap)
                r[i++] = (T)it.next();
            else if (cap < Integer.MAX_VALUE) { // expand
                int newCap = (cap * 3) / 2 + 1;
                if (newCap <= cap) // integer overflow
                    newCap = Integer.MAX_VALUE;
                r = Arrays.copyOf(r, newCap);
            } else // can't expand
                throw new OutOfMemoryError("Required array size too large");
        }
        // trim if overallocated
        return i == r.length ? r : Arrays.copyOf(r, i);
    }

    // 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> e = iterator();
        if (o==null) {
            while (e.hasNext()) {
                if (e.next()==null) {
                    e.remove();
                    return true;
                }
            }
        } else {
            while (e.hasNext()) {
                if (o.equals(e.next())) {
                    e.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) {
        Iterator<?> e = c.iterator();
        while (e.hasNext())
            if (!contains(e.next()))
                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;
        Iterator<? extends E> e = c.iterator();
        while (e.hasNext()) {
            if (add(e.next()))
                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<?> e = iterator();
        while (e.hasNext()) {
            if (c.contains(e.next())) {
                e.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> e = iterator();
        while (e.hasNext()) {
            if (!c.contains(e.next())) {
                e.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> e = iterator();
        while (e.hasNext()) {
            e.next();
            e.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> i = iterator();
        if (! i.hasNext())
            return "[]";

        StringBuilder sb = new StringBuilder();
        sb.append('[');
        for (;;) {
            E e = i.next();
            sb.append(e == this ? "(this Collection)" : e);
            if (! i.hasNext())
                return sb.append(']').toString();
            sb.append(", ");
        }
    }

}
Revision:	1.3
Committed:	Sat Nov 26 20:59:57 2005 UTC (18 years, 6 months ago) by jsr166
Branch:	MAIN
Changes since 1.2:	+12 -10 lines
Log Message:	small fixups
#	User	Rev	Content
1	dl	1.1	/*
2	jsr166	1.3	* %W% %E%
3	dl	1.1	*
4			* Copyright 2005 Sun Microsystems, Inc. All rights reserved.
5			* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6			*/
7
8			package java.util;
9
10			/**
11			* This class provides a skeletal implementation of the <tt>Collection</tt>
12			* interface, to minimize the effort required to implement this interface. <p>
13			*
14			* To implement an unmodifiable collection, the programmer needs only to
15			* extend this class and provide implementations for the <tt>iterator</tt> and
16			* <tt>size</tt> methods. (The iterator returned by the <tt>iterator</tt>
17			* method must implement <tt>hasNext</tt> and <tt>next</tt>.)<p>
18			*
19			* To implement a modifiable collection, the programmer must additionally
20			* override this class's <tt>add</tt> method (which otherwise throws an
21			* <tt>UnsupportedOperationException</tt>), and the iterator returned by the
22			* <tt>iterator</tt> method must additionally implement its <tt>remove</tt>
23			* method.<p>
24			*
25			* The programmer should generally provide a void (no argument) and
26			* <tt>Collection</tt> constructor, as per the recommendation in the
27			* <tt>Collection</tt> interface specification.<p>
28			*
29			* The documentation for each non-abstract methods in this class describes its
30			* implementation in detail. Each of these methods may be overridden if
31			* the collection being implemented admits a more efficient implementation.<p>
32			*
33			* This class is a member of the
34			* <a href="{@docRoot}/../guide/collections/index.html">
35			* Java Collections Framework</a>.
36			*
37			* @author Josh Bloch
38			* @author Neal Gafter
39			* @version 1.24, 01/18/03
40			* @see Collection
41			* @since 1.2
42			*/
43
44			public abstract class AbstractCollection<E> implements Collection<E> {
45			/**
46			* Sole constructor. (For invocation by subclass constructors, typically
47			* implicit.)
48			*/
49			protected AbstractCollection() {
50			}
51
52			// Query Operations
53
54			/**
55			* Returns an iterator over the elements contained in this collection.
56			*
57			* @return an iterator over the elements contained in this collection
58			*/
59			public abstract Iterator<E> iterator();
60
61			public abstract int size();
62
63			/**
64			* {@inheritDoc}
65			*
66			* <p>This implementation returns <tt>size() == 0</tt>.
67			*/
68			public boolean isEmpty() {
69			return size() == 0;
70			}
71
72			/**
73			* {@inheritDoc}
74			*
75			* <p>This implementation iterates over the elements in the collection,
76			* checking each element in turn for equality with the specified element.
77			*
78			* @throws ClassCastException {@inheritDoc}
79			* @throws NullPointerException {@inheritDoc}
80			*/
81			public boolean contains(Object o) {
82			Iterator<E> e = iterator();
83			if (o==null) {
84			while (e.hasNext())
85			if (e.next()==null)
86			return true;
87			} else {
88			while (e.hasNext())
89			if (o.equals(e.next()))
90			return true;
91			}
92			return false;
93			}
94
95			/**
96			* {@inheritDoc}
97			*
98			* <p>This implementation allocates the array to be returned, and iterates
99			* over the elements in the collection, storing each object reference in
100			* the next consecutive element of the array, starting with element 0.
101			*/
102			public Object[] toArray() {
103			// Estimate size of array; be prepared to see more or fewer elements
104			Object[] r = new Object[size()];
105			int i = 0;
106	jsr166	1.3	Iterator<E> it = iterator();
107	jsr166	1.2	while (i < r.length && it.hasNext())
108	dl	1.1	r[i++] = it.next();
109			// Trim if overallocated; expand if underallocated
110			if (i < r.length \|\| it.hasNext())
111			return resizeAndFinishToArray(r, i, it);
112			return r;
113			}
114
115			/**
116			* {@inheritDoc}
117			*
118			* <p>This implementation checks if the array is large enough to contain the
119			* collection; if not, it allocates a new array of the correct size and
120			* type (using reflection). Then, it iterates over the collection,
121			* storing each object reference in the next consecutive element of the
122			* array, starting with element 0. If the array is larger than the
123			* collection, a <tt>null</tt> is stored in the first location after the
124			* end of the collection.
125			*
126			* @throws ArrayStoreException {@inheritDoc}
127			* @throws NullPointerException {@inheritDoc}
128			*/
129			public <T> T[] toArray(T[] a) {
130			// Estimate size of array; be prepared to see more or fewer elements
131			int size = size();
132	jsr166	1.3	T[] r = a.length >= size ? a :
133	dl	1.1	(T[])java.lang.reflect.Array
134			.newInstance(a.getClass().getComponentType(), size);
135			int i = 0;
136	jsr166	1.3	Iterator<E> it = iterator();
137	jsr166	1.2	while (i < r.length && it.hasNext())
138	dl	1.1	r[i++] = (T)it.next();
139			// Trim if overallocated; expand if underallocated
140			if (it.hasNext() \|\| (r != a && i < r.length))
141			return resizeAndFinishToArray(r, i, it);
142	jsr166	1.2	if (i < r.length)
143	dl	1.1	r[i] = null; // null-terminate if provided array is too big
144			return r;
145			}
146
147			/**
148	jsr166	1.3	* Reallocates the array being used within toArray that has a
149			* different number of elements than expected, and finishes
150			* filling it from the given iterator, if necessary.
151			*
152	dl	1.1	* @param r the array
153			* @param i the next array index to fill
154			* @param it the in-progress iterator over the collection
155	jsr166	1.3	* @return array containing the elements in the given array, plus any
156			* further elements returned by the iterator, trimmed to size
157	dl	1.1	*/
158	jsr166	1.3	private static <T> T[] resizeAndFinishToArray(T[] r, int i, Iterator<?> it) {
159	jsr166	1.2	while (it.hasNext()) {
160	dl	1.1	int cap = r.length;
161			if (i < cap)
162			r[i++] = (T)it.next();
163			else if (cap < Integer.MAX_VALUE) { // expand
164			int newCap = (cap * 3) / 2 + 1;
165			if (newCap <= cap) // integer overflow
166			newCap = Integer.MAX_VALUE;
167			r = Arrays.copyOf(r, newCap);
168			} else // can't expand
169			throw new OutOfMemoryError("Required array size too large");
170			}
171			// trim if overallocated
172	jsr166	1.3	return i == r.length ? r : Arrays.copyOf(r, i);
173	dl	1.1	}
174
175			// Modification Operations
176
177			/**
178			* {@inheritDoc}
179			*
180			* <p>This implementation always throws an
181			* <tt>UnsupportedOperationException</tt>.
182			*
183			* @throws UnsupportedOperationException {@inheritDoc}
184			* @throws ClassCastException {@inheritDoc}
185			* @throws NullPointerException {@inheritDoc}
186			* @throws IllegalArgumentException {@inheritDoc}
187			* @throws IllegalStateException {@inheritDoc}
188			*/
189			public boolean add(E e) {
190			throw new UnsupportedOperationException();
191			}
192
193			/**
194			* {@inheritDoc}
195			*
196			* <p>This implementation iterates over the collection looking for the
197			* specified element. If it finds the element, it removes the element
198			* from the collection using the iterator's remove method.
199			*
200			* <p>Note that this implementation throws an
201			* <tt>UnsupportedOperationException</tt> if the iterator returned by this
202			* collection's iterator method does not implement the <tt>remove</tt>
203			* method and this collection contains the specified object.
204			*
205			* @throws UnsupportedOperationException {@inheritDoc}
206			* @throws ClassCastException {@inheritDoc}
207			* @throws NullPointerException {@inheritDoc}
208			*/
209			public boolean remove(Object o) {
210			Iterator<E> e = iterator();
211			if (o==null) {
212			while (e.hasNext()) {
213			if (e.next()==null) {
214			e.remove();
215			return true;
216			}
217			}
218			} else {
219			while (e.hasNext()) {
220			if (o.equals(e.next())) {
221			e.remove();
222			return true;
223			}
224			}
225			}
226			return false;
227			}
228
229
230			// Bulk Operations
231
232			/**
233			* {@inheritDoc}
234			*
235			* <p>This implementation iterates over the specified collection,
236			* checking each element returned by the iterator in turn to see
237			* if it's contained in this collection. If all elements are so
238			* contained <tt>true</tt> is returned, otherwise <tt>false</tt>.
239			*
240			* @throws ClassCastException {@inheritDoc}
241			* @throws NullPointerException {@inheritDoc}
242			* @see #contains(Object)
243			*/
244			public boolean containsAll(Collection<?> c) {
245			Iterator<?> e = c.iterator();
246			while (e.hasNext())
247			if (!contains(e.next()))
248			return false;
249			return true;
250			}
251
252			/**
253			* {@inheritDoc}
254			*
255			* <p>This implementation iterates over the specified collection, and adds
256			* each object returned by the iterator to this collection, in turn.
257			*
258			* <p>Note that this implementation will throw an
259			* <tt>UnsupportedOperationException</tt> unless <tt>add</tt> is
260			* overridden (assuming the specified collection is non-empty).
261			*
262			* @throws UnsupportedOperationException {@inheritDoc}
263			* @throws ClassCastException {@inheritDoc}
264			* @throws NullPointerException {@inheritDoc}
265			* @throws IllegalArgumentException {@inheritDoc}
266			* @throws IllegalStateException {@inheritDoc}
267			*
268			* @see #add(Object)
269			*/
270			public boolean addAll(Collection<? extends E> c) {
271			boolean modified = false;
272			Iterator<? extends E> e = c.iterator();
273			while (e.hasNext()) {
274			if (add(e.next()))
275			modified = true;
276			}
277			return modified;
278			}
279
280			/**
281			* {@inheritDoc}
282			*
283			* <p>This implementation iterates over this collection, checking each
284			* element returned by the iterator in turn to see if it's contained
285			* in the specified collection. If it's so contained, it's removed from
286			* this collection with the iterator's <tt>remove</tt> method.
287			*
288			* <p>Note that this implementation will throw an
289			* <tt>UnsupportedOperationException</tt> if the iterator returned by the
290			* <tt>iterator</tt> method does not implement the <tt>remove</tt> method
291			* and this collection contains one or more elements in common with the
292			* specified collection.
293			*
294			* @throws UnsupportedOperationException {@inheritDoc}
295			* @throws ClassCastException {@inheritDoc}
296			* @throws NullPointerException {@inheritDoc}
297			*
298			* @see #remove(Object)
299			* @see #contains(Object)
300			*/
301			public boolean removeAll(Collection<?> c) {
302			boolean modified = false;
303			Iterator<?> e = iterator();
304			while (e.hasNext()) {
305			if (c.contains(e.next())) {
306			e.remove();
307			modified = true;
308			}
309			}
310			return modified;
311			}
312
313			/**
314			* {@inheritDoc}
315			*
316			* <p>This implementation iterates over this collection, checking each
317			* element returned by the iterator in turn to see if it's contained
318			* in the specified collection. If it's not so contained, it's removed
319			* from this collection with the iterator's <tt>remove</tt> method.
320			*
321			* <p>Note that this implementation will throw an
322			* <tt>UnsupportedOperationException</tt> if the iterator returned by the
323			* <tt>iterator</tt> method does not implement the <tt>remove</tt> method
324			* and this collection contains one or more elements not present in the
325			* specified collection.
326			*
327			* @throws UnsupportedOperationException {@inheritDoc}
328			* @throws ClassCastException {@inheritDoc}
329			* @throws NullPointerException {@inheritDoc}
330			*
331			* @see #remove(Object)
332			* @see #contains(Object)
333			*/
334			public boolean retainAll(Collection<?> c) {
335			boolean modified = false;
336			Iterator<E> e = iterator();
337			while (e.hasNext()) {
338			if (!c.contains(e.next())) {
339			e.remove();
340			modified = true;
341			}
342			}
343			return modified;
344			}
345
346			/**
347			* {@inheritDoc}
348			*
349			* <p>This implementation iterates over this collection, removing each
350			* element using the <tt>Iterator.remove</tt> operation. Most
351			* implementations will probably choose to override this method for
352			* efficiency.
353			*
354			* <p>Note that this implementation will throw an
355			* <tt>UnsupportedOperationException</tt> if the iterator returned by this
356			* collection's <tt>iterator</tt> method does not implement the
357			* <tt>remove</tt> method and this collection is non-empty.
358			*
359			* @throws UnsupportedOperationException {@inheritDoc}
360			*/
361			public void clear() {
362			Iterator<E> e = iterator();
363			while (e.hasNext()) {
364			e.next();
365			e.remove();
366			}
367			}
368
369
370			// String conversion
371
372			/**
373			* Returns a string representation of this collection. The string
374			* representation consists of a list of the collection's elements in the
375			* order they are returned by its iterator, enclosed in square brackets
376			* (<tt>"[]"</tt>). Adjacent elements are separated by the characters
377			* <tt>", "</tt> (comma and space). Elements are converted to strings as
378			* by {@link String#valueOf(Object)}.
379			*
380			* @return a string representation of this collection
381			*/
382			public String toString() {
383			Iterator<E> i = iterator();
384			if (! i.hasNext())
385			return "[]";
386
387			StringBuilder sb = new StringBuilder();
388			sb.append('[');
389			for (;;) {
390			E e = i.next();
391			sb.append(e == this ? "(this Collection)" : e);
392			if (! i.hasNext())
393			return sb.append(']').toString();
394			sb.append(", ");
395			}
396			}
397
398			}