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1: /* AbstractSet.java -- Abstract implementation of most of Set 2: Copyright (C) 1998, 2000, 2001, 2005 Free Software Foundation, Inc. 3: 4: This file is part of GNU Classpath. 5: 6: GNU Classpath is free software; you can redistribute it and/or modify 7: it under the terms of the GNU General Public License as published by 8: the Free Software Foundation; either version 2, or (at your option) 9: any later version. 10: 11: GNU Classpath is distributed in the hope that it will be useful, but 12: WITHOUT ANY WARRANTY; without even the implied warranty of 13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14: General Public License for more details. 15: 16: You should have received a copy of the GNU General Public License 17: along with GNU Classpath; see the file COPYING. If not, write to the 18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 19: 02110-1301 USA. 20: 21: Linking this library statically or dynamically with other modules is 22: making a combined work based on this library. Thus, the terms and 23: conditions of the GNU General Public License cover the whole 24: combination. 25: 26: As a special exception, the copyright holders of this library give you 27: permission to link this library with independent modules to produce an 28: executable, regardless of the license terms of these independent 29: modules, and to copy and distribute the resulting executable under 30: terms of your choice, provided that you also meet, for each linked 31: independent module, the terms and conditions of the license of that 32: module. An independent module is a module which is not derived from 33: or based on this library. If you modify this library, you may extend 34: this exception to your version of the library, but you are not 35: obligated to do so. If you do not wish to do so, delete this 36: exception statement from your version. */ 37: 38: 39: package java.util; 40: 41: /** 42: * An abstract implementation of Set to make it easier to create your own 43: * implementations. In order to create a Set, subclass AbstractSet and 44: * implement the same methods that are required for AbstractCollection 45: * (although these methods must of course meet the requirements that Set puts 46: * on them - specifically, no element may be in the set more than once). This 47: * class simply provides implementations of equals() and hashCode() to fulfil 48: * the requirements placed on them by the Set interface. 49: * 50: * @author Original author unknown 51: * @author Eric Blake (ebb9@email.byu.edu) 52: * @see Collection 53: * @see AbstractCollection 54: * @see Set 55: * @see HashSet 56: * @see TreeSet 57: * @see LinkedHashSet 58: * @since 1.2 59: * @status updated to 1.4 60: */ 61: public abstract class AbstractSet extends AbstractCollection implements Set 62: { 63: /** 64: * The main constructor, for use by subclasses. 65: */ 66: protected AbstractSet() 67: { 68: } 69: 70: /** 71: * Tests whether the given object is equal to this Set. This implementation 72: * first checks whether this set <em>is</em> the given object, and returns 73: * true if so. Otherwise, if o is a Set and is the same size as this one, it 74: * returns the result of calling containsAll on the given Set. Otherwise, it 75: * returns false. 76: * 77: * @param o the Object to be tested for equality with this Set 78: * @return true if the given object is equal to this Set 79: */ 80: public boolean equals(Object o) 81: { 82: return (o == this || 83: (o instanceof Set && ((Set) o).size() == size() 84: && containsAll((Collection) o))); 85: } 86: 87: /** 88: * Returns a hash code for this Set. The hash code of a Set is the sum of the 89: * hash codes of all its elements, except that the hash code of null is 90: * defined to be zero. This implementation obtains an Iterator over the Set, 91: * and sums the results. 92: * 93: * @return a hash code for this Set 94: */ 95: public int hashCode() 96: { 97: Iterator itr = iterator(); 98: int hash = 0; 99: int pos = size(); 100: while (--pos >= 0) 101: hash += hashCode(itr.next()); 102: return hash; 103: } 104: 105: /** 106: * Removes from this set all elements in the given collection (optional 107: * operation). This implementation uses <code>size()</code> to determine 108: * the smaller collection. Then, if this set is smaller, it iterates 109: * over the set, calling Iterator.remove if the collection contains 110: * the element. If this set is larger, it iterates over the collection, 111: * calling Set.remove for all elements in the collection. Note that 112: * this operation will fail if a remove methods is not supported. 113: * 114: * @param c the collection of elements to remove 115: * @return true if the set was modified as a result 116: * @throws UnsupportedOperationException if remove is not supported 117: * @throws NullPointerException if the collection is null 118: * @see AbstractCollection#remove(Object) 119: * @see Collection#contains(Object) 120: * @see Iterator#remove() 121: */ 122: public boolean removeAll(Collection c) 123: { 124: int oldsize = size(); 125: int count = c.size(); 126: Iterator i; 127: if (oldsize < count) 128: { 129: for (i = iterator(), count = oldsize; count > 0; count--) 130: if (c.contains(i.next())) 131: i.remove(); 132: } 133: else 134: for (i = c.iterator(); count > 0; count--) 135: remove(i.next()); 136: return oldsize != size(); 137: } 138: 139: }