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/*
 * Copyright (c) 1997, 2018 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 com.sun.xml.bind.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:
 *
 * 
    *
  1. Push/pop operation. *
  2. 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(); } }





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