/* | |
* Copyright 2001-2004 The Apache Software Foundation | |
* | |
* Licensed under the Apache License, Version 2.0 (the "License"); | |
* you may not use this file except in compliance with the License. | |
* You may obtain a copy of the License at | |
* | |
* http://www.apache.org/licenses/LICENSE-2.0 | |
* | |
* Unless required by applicable law or agreed to in writing, software | |
* distributed under the License is distributed on an "AS IS" BASIS, | |
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
* See the License for the specific language governing permissions and | |
* limitations under the License. | |
*/ | |
package org.apache.axis2.util; | |
import java.util.ArrayList; | |
import java.util.EmptyStackException; | |
/** | |
* An implementation of the {@link java.util.Stack} API that is based on an | |
* <code>ArrayList</code> instead of a <code>Vector</code>, so it is not | |
* synchronized to protect against multi-threaded access. The implementation | |
* is therefore operates faster in environments where you do not need to | |
* worry about multiple thread contention. | |
* <p> | |
* The removal order of an <code>ArrayStack</code> is based on insertion | |
* order: The most recently added element is removed first. The iteration | |
* order is <i>not</i> the same as the removal order. The iterator returns | |
* elements from the bottom up, whereas the {@link #remove()} method removes | |
* them from the top down. | |
* <p> | |
* Unlike <code>Stack</code>, <code>ArrayStack</code> accepts null entries. | |
*/ | |
public class ArrayStack extends ArrayList { | |
/** Ensure serialization compatibility */ | |
private static final long serialVersionUID = 2130079159931574599L; | |
/** | |
* Constructs a new empty <code>ArrayStack</code>. The initial size | |
* is controlled by <code>ArrayList</code> and is currently 10. | |
*/ | |
public ArrayStack() { | |
super(); | |
} | |
/** | |
* Constructs a new empty <code>ArrayStack</code> with an initial size. | |
* | |
* @param initialSize the initial size to use | |
* @throws IllegalArgumentException if the specified initial size | |
* is negative | |
*/ | |
public ArrayStack(int initialSize) { | |
super(initialSize); | |
} | |
/** | |
* Return <code>true</code> if this stack is currently empty. | |
* <p> | |
* This method exists for compatibility with <code>java.util.Stack</code>. | |
* New users of this class should use <code>isEmpty</code> instead. | |
* | |
* @return true if the stack is currently empty | |
*/ | |
public boolean empty() { | |
return isEmpty(); | |
} | |
/** | |
* Returns the top item off of this stack without removing it. | |
* | |
* @return the top item on the stack | |
* @throws EmptyStackException if the stack is empty | |
*/ | |
public Object peek() throws EmptyStackException { | |
int n = size(); | |
if (n <= 0) { | |
throw new EmptyStackException(); | |
} else { | |
return get(n - 1); | |
} | |
} | |
/** | |
* Returns the n'th item down (zero-relative) from the top of this | |
* stack without removing it. | |
* | |
* @param n the number of items down to go | |
* @return the n'th item on the stack, zero relative | |
* @throws EmptyStackException if there are not enough items on the | |
* stack to satisfy this request | |
*/ | |
public Object peek(int n) throws EmptyStackException { | |
int m = (size() - n) - 1; | |
if (m < 0) { | |
throw new EmptyStackException(); | |
} else { | |
return get(m); | |
} | |
} | |
/** | |
* Pops the top item off of this stack and return it. | |
* | |
* @return the top item on the stack | |
* @throws EmptyStackException if the stack is empty | |
*/ | |
public Object pop() throws EmptyStackException { | |
int n = size(); | |
if (n <= 0) { | |
throw new EmptyStackException(); | |
} else { | |
return remove(n - 1); | |
} | |
} | |
/** | |
* Pushes a new item onto the top of this stack. The pushed item is also | |
* returned. This is equivalent to calling <code>add</code>. | |
* | |
* @param item the item to be added | |
* @return the item just pushed | |
*/ | |
public Object push(Object item) { | |
add(item); | |
return item; | |
} | |
/** | |
* Returns the one-based position of the distance from the top that the | |
* specified object exists on this stack, where the top-most element is | |
* considered to be at distance <code>1</code>. If the object is not | |
* present on the stack, return <code>-1</code> instead. The | |
* <code>equals()</code> method is used to compare to the items | |
* in this stack. | |
* | |
* @param object the object to be searched for | |
* @return the 1-based depth into the stack of the object, or -1 if not found | |
*/ | |
public int search(Object object) { | |
int i = size() - 1; // Current index | |
int n = 1; // Current distance | |
while (i >= 0) { | |
Object current = get(i); | |
if ((object == null && current == null) || | |
(object != null && object.equals(current))) { | |
return n; | |
} | |
i--; | |
n++; | |
} | |
return -1; | |
} | |
/** | |
* Returns the element on the top of the stack. | |
* | |
* @return the element on the top of the stack | |
* @throws EmptyStackException if the stack is empty | |
*/ | |
public Object get() { | |
int size = size(); | |
if (size == 0) { | |
throw new EmptyStackException(); | |
} | |
return get(size - 1); | |
} | |
/** | |
* Removes the element on the top of the stack. | |
* | |
* @return the removed element | |
* @throws EmptyStackException if the stack is empty | |
*/ | |
public Object remove() { | |
int size = size(); | |
if (size == 0) { | |
throw new EmptyStackException(); | |
} | |
return remove(size - 1); | |
} | |
} |