125 lines
3.2 KiB
Java
125 lines
3.2 KiB
Java
//******************************************************************************
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//
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// File: PairBase.java
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// Package: edu.rit.util
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// Unit: Class edu.rit.util.PairBase
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//
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// This Java source file is copyright (C) 2015 by Alan Kaminsky. All rights
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// reserved. For further information, contact the author, Alan Kaminsky, at
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// ark@cs.rit.edu.
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//
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// This Java source file is part of the Parallel Java 2 Library ("PJ2"). PJ2 is
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// free software; you can redistribute it and/or modify it under the terms of
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// the GNU General Public License as published by the Free Software Foundation;
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// either version 3 of the License, or (at your option) any later version.
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//
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// PJ2 is distributed in the hope that it will be useful, but WITHOUT ANY
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// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
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// A PARTICULAR PURPOSE. See the GNU General Public License for more details.
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//
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// A copy of the GNU General Public License is provided in the file gpl.txt. You
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// may also obtain a copy of the GNU General Public License on the World Wide
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// Web at http://www.gnu.org/licenses/gpl.html.
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//
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//******************************************************************************
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package edu.rit.util;
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import edu.rit.io.Streamable;
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/**
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* Class PairBase is the abstract base class for a pair consisting of a key and
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* its associated value. The key is defined in the base class; the value is
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* defined in a subclass. The key must be an object suitable for use in a hashed
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* data structure; that is, the key class must define the {@link
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* Object#equals(Object) equals()} and {@link Object#hashCode() hashCode()}
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* methods properly. The key may be null. Once a key is stored in a pair, the
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* state of the key must not be altered.
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* <P>
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* Class PairBase is streamable. For object streaming to work properly, the key
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* class must be streamable or serializable.
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*
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* @param <K> Key data type.
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*
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* @author Alan Kaminsky
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* @version 18-Jan-2015
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*/
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public abstract class PairBase<K>
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implements Streamable
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{
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// Hidden data members.
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/**
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* The pair's key.
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*/
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protected K key;
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// Exported constructors.
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/**
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* Construct a new pair. The key is null.
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*/
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public PairBase()
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{
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}
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/**
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* Construct a new pair with the given key.
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*
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* @param key Key.
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*/
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public PairBase
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(K key)
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{
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this.key = key;
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}
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// Exported operations.
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/**
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* Returns this pair's key.
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*
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* @return Key.
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*/
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public K key()
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{
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return key;
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}
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/**
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* Determine if this pair is equal to the given object. The pairs are equal
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* if their keys are equal, as determined by the key class's {@link
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* Object#equals(Object) equals()} method.
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*
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* @param obj Object to test.
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*
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* @return True if this pair is equal to <TT>obj</TT>, false otherwise.
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*/
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public boolean equals
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(Object obj)
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{
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if (obj instanceof PairBase)
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{
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PairBase pair = (PairBase)obj;
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return
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(this.key == null && pair.key == null) ||
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(this.key != null && this.key.equals (pair.key));
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}
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else
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return false;
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}
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/**
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* Returns a hash code for this pair. The hash code is that of the key, as
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* returned by the key class's {@link Object#hashCode() hashCode()} method.
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*
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* @return Hash code.
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*/
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public int hashCode()
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{
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return key == null ? 0 : key.hashCode();
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}
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}
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