001: /*
002: * Copyright 1997-2006 Sun Microsystems, Inc. All Rights Reserved.
003: * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004: *
005: * This code is free software; you can redistribute it and/or modify it
006: * under the terms of the GNU General Public License version 2 only, as
007: * published by the Free Software Foundation. Sun designates this
008: * particular file as subject to the "Classpath" exception as provided
009: * by Sun in the LICENSE file that accompanied this code.
010: *
011: * This code is distributed in the hope that it will be useful, but WITHOUT
012: * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
013: * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
014: * version 2 for more details (a copy is included in the LICENSE file that
015: * accompanied this code).
016: *
017: * You should have received a copy of the GNU General Public License version
018: * 2 along with this work; if not, write to the Free Software Foundation,
019: * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
020: *
021: * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
022: * CA 95054 USA or visit www.sun.com if you need additional information or
023: * have any questions.
024: */
025:
026: package java.util;
027:
028: /**
029: * A collection that contains no duplicate elements. More formally, sets
030: * contain no pair of elements <code>e1</code> and <code>e2</code> such that
031: * <code>e1.equals(e2)</code>, and at most one null element. As implied by
032: * its name, this interface models the mathematical <i>set</i> abstraction.
033: *
034: * <p>The <tt>Set</tt> interface places additional stipulations, beyond those
035: * inherited from the <tt>Collection</tt> interface, on the contracts of all
036: * constructors and on the contracts of the <tt>add</tt>, <tt>equals</tt> and
037: * <tt>hashCode</tt> methods. Declarations for other inherited methods are
038: * also included here for convenience. (The specifications accompanying these
039: * declarations have been tailored to the <tt>Set</tt> interface, but they do
040: * not contain any additional stipulations.)
041: *
042: * <p>The additional stipulation on constructors is, not surprisingly,
043: * that all constructors must create a set that contains no duplicate elements
044: * (as defined above).
045: *
046: * <p>Note: Great care must be exercised if mutable objects are used as set
047: * elements. The behavior of a set is not specified if the value of an object
048: * is changed in a manner that affects <tt>equals</tt> comparisons while the
049: * object is an element in the set. A special case of this prohibition is
050: * that it is not permissible for a set to contain itself as an element.
051: *
052: * <p>Some set implementations have restrictions on the elements that
053: * they may contain. For example, some implementations prohibit null elements,
054: * and some have restrictions on the types of their elements. Attempting to
055: * add an ineligible element throws an unchecked exception, typically
056: * <tt>NullPointerException</tt> or <tt>ClassCastException</tt>. Attempting
057: * to query the presence of an ineligible element may throw an exception,
058: * or it may simply return false; some implementations will exhibit the former
059: * behavior and some will exhibit the latter. More generally, attempting an
060: * operation on an ineligible element whose completion would not result in
061: * the insertion of an ineligible element into the set may throw an
062: * exception or it may succeed, at the option of the implementation.
063: * Such exceptions are marked as "optional" in the specification for this
064: * interface.
065: *
066: * <p>This interface is a member of the
067: * <a href="{@docRoot}/../technotes/guides/collections/index.html">
068: * Java Collections Framework</a>.
069: *
070: * @param <E> the type of elements maintained by this set
071: *
072: * @author Josh Bloch
073: * @author Neal Gafter
074: * @version 1.45, 05/05/07
075: * @see Collection
076: * @see List
077: * @see SortedSet
078: * @see HashSet
079: * @see TreeSet
080: * @see AbstractSet
081: * @see Collections#singleton(java.lang.Object)
082: * @see Collections#EMPTY_SET
083: * @since 1.2
084: */
085:
086: public interface Set<E> extends Collection<E> {
087: // Query Operations
088:
089: /**
090: * Returns the number of elements in this set (its cardinality). If this
091: * set contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
092: * <tt>Integer.MAX_VALUE</tt>.
093: *
094: * @return the number of elements in this set (its cardinality)
095: */
096: int size();
097:
098: /**
099: * Returns <tt>true</tt> if this set contains no elements.
100: *
101: * @return <tt>true</tt> if this set contains no elements
102: */
103: boolean isEmpty();
104:
105: /**
106: * Returns <tt>true</tt> if this set contains the specified element.
107: * More formally, returns <tt>true</tt> if and only if this set
108: * contains an element <tt>e</tt> such that
109: * <tt>(o==null ? e==null : o.equals(e))</tt>.
110: *
111: * @param o element whose presence in this set is to be tested
112: * @return <tt>true</tt> if this set contains the specified element
113: * @throws ClassCastException if the type of the specified element
114: * is incompatible with this set (optional)
115: * @throws NullPointerException if the specified element is null and this
116: * set does not permit null elements (optional)
117: */
118: boolean contains(Object o);
119:
120: /**
121: * Returns an iterator over the elements in this set. The elements are
122: * returned in no particular order (unless this set is an instance of some
123: * class that provides a guarantee).
124: *
125: * @return an iterator over the elements in this set
126: */
127: Iterator<E> iterator();
128:
129: /**
130: * Returns an array containing all of the elements in this set.
131: * If this set makes any guarantees as to what order its elements
132: * are returned by its iterator, this method must return the
133: * elements in the same order.
134: *
135: * <p>The returned array will be "safe" in that no references to it
136: * are maintained by this set. (In other words, this method must
137: * allocate a new array even if this set is backed by an array).
138: * The caller is thus free to modify the returned array.
139: *
140: * <p>This method acts as bridge between array-based and collection-based
141: * APIs.
142: *
143: * @return an array containing all the elements in this set
144: */
145: Object[] toArray();
146:
147: /**
148: * Returns an array containing all of the elements in this set; the
149: * runtime type of the returned array is that of the specified array.
150: * If the set fits in the specified array, it is returned therein.
151: * Otherwise, a new array is allocated with the runtime type of the
152: * specified array and the size of this set.
153: *
154: * <p>If this set fits in the specified array with room to spare
155: * (i.e., the array has more elements than this set), the element in
156: * the array immediately following the end of the set is set to
157: * <tt>null</tt>. (This is useful in determining the length of this
158: * set <i>only</i> if the caller knows that this set does not contain
159: * any null elements.)
160: *
161: * <p>If this set makes any guarantees as to what order its elements
162: * are returned by its iterator, this method must return the elements
163: * in the same order.
164: *
165: * <p>Like the {@link #toArray()} method, this method acts as bridge between
166: * array-based and collection-based APIs. Further, this method allows
167: * precise control over the runtime type of the output array, and may,
168: * under certain circumstances, be used to save allocation costs.
169: *
170: * <p>Suppose <tt>x</tt> is a set known to contain only strings.
171: * The following code can be used to dump the set into a newly allocated
172: * array of <tt>String</tt>:
173: *
174: * <pre>
175: * String[] y = x.toArray(new String[0]);</pre>
176: *
177: * Note that <tt>toArray(new Object[0])</tt> is identical in function to
178: * <tt>toArray()</tt>.
179: *
180: * @param a the array into which the elements of this set are to be
181: * stored, if it is big enough; otherwise, a new array of the same
182: * runtime type is allocated for this purpose.
183: * @return an array containing all the elements in this set
184: * @throws ArrayStoreException if the runtime type of the specified array
185: * is not a supertype of the runtime type of every element in this
186: * set
187: * @throws NullPointerException if the specified array is null
188: */
189: <T> T[] toArray(T[] a);
190:
191: // Modification Operations
192:
193: /**
194: * Adds the specified element to this set if it is not already present
195: * (optional operation). More formally, adds the specified element
196: * <tt>e</tt> to this set if the set contains no element <tt>e2</tt>
197: * such that
198: * <tt>(e==null ? e2==null : e.equals(e2))</tt>.
199: * If this set already contains the element, the call leaves the set
200: * unchanged and returns <tt>false</tt>. In combination with the
201: * restriction on constructors, this ensures that sets never contain
202: * duplicate elements.
203: *
204: * <p>The stipulation above does not imply that sets must accept all
205: * elements; sets may refuse to add any particular element, including
206: * <tt>null</tt>, and throw an exception, as described in the
207: * specification for {@link Collection#add Collection.add}.
208: * Individual set implementations should clearly document any
209: * restrictions on the elements that they may contain.
210: *
211: * @param e element to be added to this set
212: * @return <tt>true</tt> if this set did not already contain the specified
213: * element
214: * @throws UnsupportedOperationException if the <tt>add</tt> operation
215: * is not supported by this set
216: * @throws ClassCastException if the class of the specified element
217: * prevents it from being added to this set
218: * @throws NullPointerException if the specified element is null and this
219: * set does not permit null elements
220: * @throws IllegalArgumentException if some property of the specified element
221: * prevents it from being added to this set
222: */
223: boolean add(E e);
224:
225: /**
226: * Removes the specified element from this set if it is present
227: * (optional operation). More formally, removes an element <tt>e</tt>
228: * such that
229: * <tt>(o==null ? e==null : o.equals(e))</tt>, if
230: * this set contains such an element. Returns <tt>true</tt> if this set
231: * contained the element (or equivalently, if this set changed as a
232: * result of the call). (This set will not contain the element once the
233: * call returns.)
234: *
235: * @param o object to be removed from this set, if present
236: * @return <tt>true</tt> if this set contained the specified element
237: * @throws ClassCastException if the type of the specified element
238: * is incompatible with this set (optional)
239: * @throws NullPointerException if the specified element is null and this
240: * set does not permit null elements (optional)
241: * @throws UnsupportedOperationException if the <tt>remove</tt> operation
242: * is not supported by this set
243: */
244: boolean remove(Object o);
245:
246: // Bulk Operations
247:
248: /**
249: * Returns <tt>true</tt> if this set contains all of the elements of the
250: * specified collection. If the specified collection is also a set, this
251: * method returns <tt>true</tt> if it is a <i>subset</i> of this set.
252: *
253: * @param c collection to be checked for containment in this set
254: * @return <tt>true</tt> if this set contains all of the elements of the
255: * specified collection
256: * @throws ClassCastException if the types of one or more elements
257: * in the specified collection are incompatible with this
258: * set (optional)
259: * @throws NullPointerException if the specified collection contains one
260: * or more null elements and this set does not permit null
261: * elements (optional), or if the specified collection is null
262: * @see #contains(Object)
263: */
264: boolean containsAll(Collection<?> c);
265:
266: /**
267: * Adds all of the elements in the specified collection to this set if
268: * they're not already present (optional operation). If the specified
269: * collection is also a set, the <tt>addAll</tt> operation effectively
270: * modifies this set so that its value is the <i>union</i> of the two
271: * sets. The behavior of this operation is undefined if the specified
272: * collection is modified while the operation is in progress.
273: *
274: * @param c collection containing elements to be added to this set
275: * @return <tt>true</tt> if this set changed as a result of the call
276: *
277: * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
278: * is not supported by this set
279: * @throws ClassCastException if the class of an element of the
280: * specified collection prevents it from being added to this set
281: * @throws NullPointerException if the specified collection contains one
282: * or more null elements and this set does not permit null
283: * elements, or if the specified collection is null
284: * @throws IllegalArgumentException if some property of an element of the
285: * specified collection prevents it from being added to this set
286: * @see #add(Object)
287: */
288: boolean addAll(Collection<? extends E> c);
289:
290: /**
291: * Retains only the elements in this set that are contained in the
292: * specified collection (optional operation). In other words, removes
293: * from this set all of its elements that are not contained in the
294: * specified collection. If the specified collection is also a set, this
295: * operation effectively modifies this set so that its value is the
296: * <i>intersection</i> of the two sets.
297: *
298: * @param c collection containing elements to be retained in this set
299: * @return <tt>true</tt> if this set changed as a result of the call
300: * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
301: * is not supported by this set
302: * @throws ClassCastException if the class of an element of this set
303: * is incompatible with the specified collection (optional)
304: * @throws NullPointerException if this set contains a null element and the
305: * specified collection does not permit null elements (optional),
306: * or if the specified collection is null
307: * @see #remove(Object)
308: */
309: boolean retainAll(Collection<?> c);
310:
311: /**
312: * Removes from this set all of its elements that are contained in the
313: * specified collection (optional operation). If the specified
314: * collection is also a set, this operation effectively modifies this
315: * set so that its value is the <i>asymmetric set difference</i> of
316: * the two sets.
317: *
318: * @param c collection containing elements to be removed from this set
319: * @return <tt>true</tt> if this set changed as a result of the call
320: * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation
321: * is not supported by this set
322: * @throws ClassCastException if the class of an element of this set
323: * is incompatible with the specified collection (optional)
324: * @throws NullPointerException if this set contains a null element and the
325: * specified collection does not permit null elements (optional),
326: * or if the specified collection is null
327: * @see #remove(Object)
328: * @see #contains(Object)
329: */
330: boolean removeAll(Collection<?> c);
331:
332: /**
333: * Removes all of the elements from this set (optional operation).
334: * The set will be empty after this call returns.
335: *
336: * @throws UnsupportedOperationException if the <tt>clear</tt> method
337: * is not supported by this set
338: */
339: void clear();
340:
341: // Comparison and hashing
342:
343: /**
344: * Compares the specified object with this set for equality. Returns
345: * <tt>true</tt> if the specified object is also a set, the two sets
346: * have the same size, and every member of the specified set is
347: * contained in this set (or equivalently, every member of this set is
348: * contained in the specified set). This definition ensures that the
349: * equals method works properly across different implementations of the
350: * set interface.
351: *
352: * @param o object to be compared for equality with this set
353: * @return <tt>true</tt> if the specified object is equal to this set
354: */
355: boolean equals(Object o);
356:
357: /**
358: * Returns the hash code value for this set. The hash code of a set is
359: * defined to be the sum of the hash codes of the elements in the set,
360: * where the hash code of a <tt>null</tt> element is defined to be zero.
361: * This ensures that <tt>s1.equals(s2)</tt> implies that
362: * <tt>s1.hashCode()==s2.hashCode()</tt> for any two sets <tt>s1</tt>
363: * and <tt>s2</tt>, as required by the general contract of
364: * {@link Object#hashCode}.
365: *
366: * @return the hash code value for this set
367: * @see Object#equals(Object)
368: * @see Set#equals(Object)
369: */
370: int hashCode();
371: }
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