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128 lines (114 loc) · 3.86 KB
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/*
* Copyright (c) 2007 Sun Microsystems, Inc. All rights reserved.
*
* Sun Microsystems, Inc. has intellectual property rights relating to technology embodied in the product
* that is described in this document. In particular, and without limitation, these intellectual property
* rights may include one or more of the U.S. patents listed at http://www.sun.com/patents and one or
* more additional patents or pending patent applications in the U.S. and in other countries.
*
* U.S. Government Rights - Commercial software. Government users are subject to the Sun
* Microsystems, Inc. standard license agreement and applicable provisions of the FAR and its
* supplements.
*
* Use is subject to license terms. Sun, Sun Microsystems, the Sun logo, Java and Solaris are trademarks or
* registered trademarks of Sun Microsystems, Inc. in the U.S. and other countries. All SPARC trademarks
* are used under license and are trademarks or registered trademarks of SPARC International, Inc. in the
* U.S. and other countries.
*
* UNIX is a registered trademark in the U.S. and other countries, exclusively licensed through X/Open
* Company, Ltd.
*/
package com.sun.max.util;
import java.util.*;
import com.sun.max.program.*;
/**
* An array-based recording of the history of a value, with
* time expressed as the number of generations back from the current generation (0).
*
* @author Michael Van De Vanter
*/
public class ArrayValueHistory<E> {
private final ArrayDeque<E> generations;
private final int limit;
private int age = -1;
public ArrayValueHistory(int limit) {
this.generations = new ArrayDeque<E>();
this.limit = limit;
}
public ArrayValueHistory() {
this (Integer.MAX_VALUE);
}
/**
* Adds a new value, which becomes the current generation.
* The generation of all previously recorded values increases by 1.
*/
public void add(E newValue) {
if (generations.size() > 0) {
if (newValue.equals(generations.getFirst())) {
if (age >= 0) {
age++;
}
} else {
age = 0;
}
}
generations.addFirst(newValue);
if (generations.size() > limit) {
generations.removeLast();
}
}
/**
* @return the "current" value (at generation 0).
* Error if no values have been recorded.
*/
public E get() {
if (generations.size() > 0) {
return generations.getFirst();
}
ProgramError.unexpected("empty history");
return null;
}
/**
* @return The value at a specified generation.
* Error if generation does not exist.
*/
public E get(int generation) {
final Iterator<E> iterator = generations.iterator();
int index = 0;
while (iterator.hasNext()) {
if (index == generation) {
return iterator.next();
}
index++;
}
ProgramError.unexpected("exceeded history");
return null;
}
/**
* @return the age, in generations, of the current value, since recording began.
* 0 if different from immediate predecessor; -1 if no different value ever recorded
* Comparison uses {@linkplain Object#equals(Object) equals}.
*/
public int getAge() {
return age;
}
/**
* @return the maximum number of generations that can be recorded.
*/
public int getLimit() {
return limit;
}
/**
* @return the number of generations recorded; initially 0.
*/
public int getSize() {
return generations.size();
}
/**
* @return iteration of the values recorded in the history, starting with the current
* generation and proceeding backward in time.
*/
public Iterator<E> values() {
return generations.iterator();
}
}