org.glassfish.jaxb.runtime.v2.util.CollisionCheckStack Maven / Gradle / Ivy
/*
* Copyright (c) 1997, 2020 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Distribution License v. 1.0, which is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
package org.glassfish.jaxb.runtime.v2.util;
import java.util.AbstractList;
import java.util.Arrays;
import java.util.List;
import java.util.Stack;
/**
* {@link Stack}-like data structure that allows the following efficient operations:
*
*
* - Push/pop operation.
*
- Duplicate check. When an object that's already in the stack is pushed,
* this class will tell you so.
*
*
*
* Object equality is their identity equality.
*
*
* This class implements {@link List} for accessing items in the stack,
* but {@link List} methods that alter the stack is not supported.
*
* @author Kohsuke Kawaguchi
*/
public final class CollisionCheckStack extends AbstractList {
private Object[] data;
private int[] next;
private int size = 0;
private boolean latestPushResult = false;
/**
* True if the check shall be done by using the object identity.
* False if the check shall be done with the equals method.
*/
private boolean useIdentity = true;
// for our purpose, there isn't much point in resizing this as we don't expect
// the stack to grow that much.
private final int[] initialHash;
public CollisionCheckStack() {
initialHash = new int[17];
data = new Object[16];
next = new int[16];
}
/**
* Set to false to use {@link Object#equals(Object)} to detect cycles.
* This method can be only used when the stack is empty.
*/
public void setUseIdentity(boolean useIdentity) {
this.useIdentity = useIdentity;
}
public boolean getUseIdentity() {
return useIdentity;
}
public boolean getLatestPushResult() {
return latestPushResult;
}
/**
* Pushes a new object to the stack.
*
* @return
* true if this object has already been pushed
*/
public boolean push(E o) {
if(data.length==size)
expandCapacity();
data[size] = o;
int hash = hash(o);
boolean r = findDuplicate(o, hash);
next[size] = initialHash[hash];
initialHash[hash] = size+1;
size++;
this.latestPushResult = r;
return latestPushResult;
}
/**
* Pushes a new object to the stack without making it participate
* with the collision check.
*/
public void pushNocheck(E o) {
if(data.length==size)
expandCapacity();
data[size] = o;
next[size] = -1;
size++;
}
public boolean findDuplicate(E o) {
int hash = hash(o);
return findDuplicate(o, hash);
}
@Override
public E get(int index) {
return (E)data[index];
}
@Override
public int size() {
return size;
}
private int hash(Object o) {
return ((useIdentity?System.identityHashCode(o):o.hashCode())&0x7FFFFFFF) % initialHash.length;
}
/**
* Pops an object from the stack
*/
public E pop() {
size--;
Object o = data[size];
data[size] = null; // keeping references too long == memory leak
int n = next[size];
if(n<0) {
// pushed by nocheck. no need to update hash
} else {
int hash = hash(o);
assert initialHash[hash]==size+1;
initialHash[hash] = n;
}
return (E)o;
}
/**
* Returns the top of the stack.
*/
public E peek() {
return (E)data[size-1];
}
private boolean findDuplicate(E o, int hash) {
int p = initialHash[hash];
while(p!=0) {
p--;
Object existing = data[p];
if (useIdentity) {
if(existing==o) return true;
} else {
if (o.equals(existing)) return true;
}
p = next[p];
}
return false;
}
private void expandCapacity() {
int oldSize = data.length;
int newSize = oldSize * 2;
Object[] d = new Object[newSize];
int[] n = new int[newSize];
System.arraycopy(data,0,d,0,oldSize);
System.arraycopy(next,0,n,0,oldSize);
data = d;
next = n;
}
/**
* Clears all the contents in the stack.
*/
public void reset() {
if(size>0) {
size = 0;
Arrays.fill(initialHash,0);
}
}
/**
* String that represents the cycle.
*/
public String getCycleString() {
StringBuilder sb = new StringBuilder();
int i=size()-1;
E obj = get(i);
sb.append(obj);
Object x;
do {
sb.append(" -> ");
x = get(--i);
sb.append(x);
} while(obj!=x);
return sb.toString();
}
}