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/* * @(#)AbstractSet.java 1.29 06/04/21 * * Copyright 2006 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>Set</tt> * interface to minimize the effort required to implement this * interface. <p> * * The process of implementing a set by extending this class is identical * to that of implementing a Collection by extending AbstractCollection, * except that all of the methods and constructors in subclasses of this * class must obey the additional constraints imposed by the <tt>Set</tt> * interface (for instance, the add method must not permit addition of * multiple instances of an object to a set).<p> * * Note that this class does not override any of the implementations from * the <tt>AbstractCollection</tt> class. It merely adds implementations * for <tt>equals</tt> and <tt>hashCode</tt>.<p> * * This class is a member of the * <a href="{@docRoot}/../technotes/guides/collections/index.html"> * Java Collections Framework</a>. * * @param <E> the type of elements maintained by this set * * @author Josh Bloch * @author Neal Gafter * @version 1.29, 04/21/06 * @see Collection * @see AbstractCollection * @see Set * @since 1.2 */ public abstract class AbstractSet<E> extends AbstractCollection<E> implements Set<E> { /** * Sole constructor. (For invocation by subclass constructors, typically * implicit.) */ protected AbstractSet() { } // Comparison and hashing /** * Compares the specified object with this set for equality. Returns * <tt>true</tt> if the given object is also a set, the two sets have * the same size, and every member of the given set is contained in * this set. This ensures that the <tt>equals</tt> method works * properly across different implementations of the <tt>Set</tt> * interface.<p> * * This implementation first checks if the specified object is this * set; if so it returns <tt>true</tt>. Then, it checks if the * specified object is a set whose size is identical to the size of * this set; if not, it returns false. If so, it returns * <tt>containsAll((Collection) o)</tt>. * * @param o object to be compared for equality with this set * @return <tt>true</tt> if the specified object is equal to this set */ public boolean equals(Object o) { if (o == this) return true; if (!(o instanceof Set)) return false; Collection c = (Collection) o; if (c.size() != size()) return false; try { return containsAll(c); } catch (ClassCastException unused) { return false; } catch (NullPointerException unused) { return false; } } /** * Returns the hash code value for this set. The hash code of a set is * defined to be the sum of the hash codes of the elements in the set, * where the hash code of a <tt>null</tt> element is defined to be zero. * This ensures that <tt>s1.equals(s2)</tt> implies that * <tt>s1.hashCode()==s2.hashCode()</tt> for any two sets <tt>s1</tt> * and <tt>s2</tt>, as required by the general contract of * {@link Object#hashCode}. * * <p>This implementation iterates over the set, calling the * <tt>hashCode</tt> method on each element in the set, and adding up * the results. * * @return the hash code value for this set * @see Object#equals(Object) * @see Set#equals(Object) */ public int hashCode() { int h = 0; Iterator<E> i = iterator(); while (i.hasNext()) { E obj = i.next(); if (obj != null) h += obj.hashCode(); } return h; } /** * Removes from this set all of its elements that are contained in the * specified collection (optional operation). If the specified * collection is also a set, this operation effectively modifies this * set so that its value is the <i>asymmetric set difference</i> of * the two sets. * * <p>This implementation determines which is the smaller of this set * and the specified collection, by invoking the <tt>size</tt> * method on each. If this set has fewer elements, then the * implementation iterates over this set, checking each element * returned by the iterator in turn to see if it is contained in * the specified collection. If it is so contained, it is removed * from this set with the iterator's <tt>remove</tt> method. If * the specified collection has fewer elements, then the * implementation iterates over the specified collection, removing * from this set each element returned by the iterator, using this * set'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. * * @param c collection containing elements to be removed from this set * @return <tt>true</tt> if this set changed as a result of the call * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation * is not supported by this set * @throws ClassCastException if the class of an element of this set * is incompatible with the specified collection (optional) * @throws NullPointerException if this set contains a null element and the * specified collection does not permit null elements (optional), * or if the specified collection is null * @see #remove(Object) * @see #contains(Object) */ public boolean removeAll(Collection<?> c) { boolean modified = false; if (size() > c.size()) { for (Iterator<?> i = c.iterator(); i.hasNext(); ) modified |= remove(i.next()); } else { for (Iterator<?> i = iterator(); i.hasNext(); ) { if (c.contains(i.next())) { i.remove(); modified = true; } } } return modified; } }