185 lines
7.3 KiB
Java
185 lines
7.3 KiB
Java
/*
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* Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.util;
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/**
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* This class provides a skeletal implementation of the {@code Set}
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* interface to minimize the effort required to implement this
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* interface. <p>
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*
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* The process of implementing a set by extending this class is identical
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* to that of implementing a Collection by extending AbstractCollection,
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* except that all of the methods and constructors in subclasses of this
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* class must obey the additional constraints imposed by the {@code Set}
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* interface (for instance, the add method must not permit addition of
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* multiple instances of an object to a set).<p>
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*
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* Note that this class does not override any of the implementations from
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* the {@code AbstractCollection} class. It merely adds implementations
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* for {@code equals} and {@code hashCode}.<p>
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*
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* This class is a member of the
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* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
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* Java Collections Framework</a>.
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*
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* @param <E> the type of elements maintained by this set
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*
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* @author Josh Bloch
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* @author Neal Gafter
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* @see Collection
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* @see AbstractCollection
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* @see Set
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* @since 1.2
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*/
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public abstract class AbstractSet<E> extends AbstractCollection<E> implements Set<E> {
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/**
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* Sole constructor. (For invocation by subclass constructors, typically
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* implicit.)
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*/
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protected AbstractSet() {
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}
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// Comparison and hashing
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/**
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* Compares the specified object with this set for equality. Returns
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* {@code true} if the given object is also a set, the two sets have
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* the same size, and every member of the given set is contained in
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* this set. This ensures that the {@code equals} method works
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* properly across different implementations of the {@code Set}
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* interface.<p>
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*
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* This implementation first checks if the specified object is this
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* set; if so it returns {@code true}. Then, it checks if the
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* specified object is a set whose size is identical to the size of
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* this set; if not, it returns false. If so, it returns
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* {@code containsAll((Collection) o)}.
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*
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* @param o object to be compared for equality with this set
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* @return {@code true} if the specified object is equal to this set
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*/
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public boolean equals(Object o) {
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if (o == this)
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return true;
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if (!(o instanceof Set))
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return false;
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Collection<?> c = (Collection<?>) o;
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if (c.size() != size())
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return false;
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try {
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return containsAll(c);
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} catch (ClassCastException | NullPointerException unused) {
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return false;
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}
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}
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/**
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* Returns the hash code value for this set. The hash code of a set is
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* defined to be the sum of the hash codes of the elements in the set,
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* where the hash code of a {@code null} element is defined to be zero.
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* This ensures that {@code s1.equals(s2)} implies that
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* {@code s1.hashCode()==s2.hashCode()} for any two sets {@code s1}
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* and {@code s2}, as required by the general contract of
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* {@link Object#hashCode}.
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*
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* <p>This implementation iterates over the set, calling the
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* {@code hashCode} method on each element in the set, and adding up
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* the results.
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*
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* @return the hash code value for this set
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* @see Object#equals(Object)
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* @see Set#equals(Object)
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*/
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public int hashCode() {
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int h = 0;
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Iterator<E> i = iterator();
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while (i.hasNext()) {
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E obj = i.next();
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if (obj != null)
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h += obj.hashCode();
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}
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return h;
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}
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/**
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* Removes from this set all of its elements that are contained in the
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* specified collection (optional operation). If the specified
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* collection is also a set, this operation effectively modifies this
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* set so that its value is the <i>asymmetric set difference</i> of
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* the two sets.
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*
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* <p>This implementation determines which is the smaller of this set
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* and the specified collection, by invoking the {@code size}
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* method on each. If this set has fewer elements, then the
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* implementation iterates over this set, checking each element
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* returned by the iterator in turn to see if it is contained in
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* the specified collection. If it is so contained, it is removed
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* from this set with the iterator's {@code remove} method. If
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* the specified collection has fewer elements, then the
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* implementation iterates over the specified collection, removing
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* from this set each element returned by the iterator, using this
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* set's {@code remove} method.
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*
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* <p>Note that this implementation will throw an
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* {@code UnsupportedOperationException} if the iterator returned by the
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* {@code iterator} method does not implement the {@code remove} method.
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*
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* @param c collection containing elements to be removed from this set
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* @return {@code true} if this set changed as a result of the call
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* @throws UnsupportedOperationException if the {@code removeAll} operation
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* is not supported by this set
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* @throws ClassCastException if the class of an element of this set
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* is incompatible with the specified collection
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* (<a href="Collection.html#optional-restrictions">optional</a>)
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* @throws NullPointerException if this set contains a null element and the
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* specified collection does not permit null elements
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* (<a href="Collection.html#optional-restrictions">optional</a>),
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* or if the specified collection is null
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* @see #remove(Object)
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* @see #contains(Object)
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*/
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public boolean removeAll(Collection<?> c) {
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Objects.requireNonNull(c);
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boolean modified = false;
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if (size() > c.size()) {
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for (Object e : c)
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modified |= remove(e);
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} else {
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for (Iterator<?> i = iterator(); i.hasNext(); ) {
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if (c.contains(i.next())) {
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i.remove();
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modified = true;
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}
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}
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}
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return modified;
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}
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}
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