/*
* 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.commons.collections;
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.
*
* @see java.util.Stack
* @since Commons Collections 1.0
* @version $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $
*
* @author Craig R. McClanahan
* @author Paul Jack
* @author Stephen Colebourne
*/
public class ArrayStack extends ArrayList implements Buffer {
/** 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 BufferUnderflowException if the stack is empty
*/
public Object get() {
int size = size();
if (size == 0) {
throw new BufferUnderflowException();
}
return get(size - 1);
}
/**
* Removes the element on the top of the stack.
*
* @return the removed element
* @throws BufferUnderflowException if the stack is empty
*/
public Object remove() {
int size = size();
if (size == 0) {
throw new BufferUnderflowException();
}
return remove(size - 1);
}
}