/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.tomcat.util.digester;
import java.io.Serial;
import java.util.ArrayList;
import java.util.EmptyStackException;
/**
* <p>
* Imported copy of the <code>ArrayStack</code> class from Commons Collections, which was the only direct dependency
* from Digester.
* </p>
* <p>
* <strong>WARNING</strong> - This class is public solely to allow it to be used from subpackages of
* <code>org.apache.commons.digester</code>. It should not be considered part of the public API of Commons Digester. If
* you want to use such a class yourself, you should use the one from Commons Collections directly.
* </p>
* <p>
* 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>
* <p>
* Unlike <code>Stack</code>, <code>ArrayStack</code> accepts null entries.
* </p>
*
* @param <E> Type of object in this stack
*
* @see java.util.Stack
*
* @since Digester 1.6 (from Commons Collections 1.0)
*/
public class ArrayStack<E> extends ArrayList<E> {
/** Ensure serialization compatibility */
@Serial
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 E 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 E 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 E 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 E push(E item) {
add(item);
return item;
}
}