Java tutorial
/* * 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: 1.17 $ $Date: 2004/02/18 01:15:42 $ * * @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); } }