| /* Stack.java - Class that provides a Last In First Out (LIFO) |
| datatype, known more commonly as a Stack |
| Copyright (C) 1998, 1999, 2001 Free Software Foundation, Inc. |
| |
| This file is part of GNU Classpath. |
| |
| GNU Classpath is free software; you can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 2, or (at your option) |
| any later version. |
| |
| GNU Classpath is distributed in the hope that it will be useful, but |
| WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| General Public License for more details. |
| |
| You should have received a copy of the GNU General Public License |
| along with GNU Classpath; see the file COPYING. If not, write to the |
| Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA |
| 02111-1307 USA. |
| |
| As a special exception, if you link this library with other files to |
| produce an executable, this library does not by itself cause the |
| resulting executable to be covered by the GNU General Public License. |
| This exception does not however invalidate any other reasons why the |
| executable file might be covered by the GNU General Public License. */ |
| |
| |
| package java.util; |
| |
| /* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3 |
| * "The Java Language Specification", ISBN 0-201-63451-1 |
| * plus online API docs for JDK 1.2 beta from http://www.javasoft.com. |
| * Status: Believed complete and correct |
| */ |
| |
| /** |
| * Stack provides a Last In First Out (LIFO) data type, commonly known |
| * as a Stack. |
| * |
| * Stack itself extends Vector and provides the additional methods |
| * for stack manipulation (push, pop, peek). |
| * |
| * @author Warren Levy <warrenl@cygnus.com> |
| * @date August 20, 1998. |
| */ |
| public class Stack extends Vector |
| { |
| // Could use Vector methods internally for the following methods |
| // but have used Vector fields directly for efficiency (i.e. this |
| // often reduces out duplicate bounds checking). |
| |
| private static final long serialVersionUID = 1224463164541339165L; |
| |
| /** |
| * This constructor creates a new Stack, initially empty |
| */ |
| public Stack() |
| { |
| super(); |
| } |
| |
| /** |
| * Pushes an Object onto the top of the stack. This method is effectively |
| * the same as addElement(item) |
| * |
| * @param item the Object to push onto the stack |
| * @returns the Object pushed onto the stack |
| * @see java.util.Vector#addElement(java.util.Object) |
| */ |
| public Object push(Object item) |
| { |
| // When growing the Stack, use the Vector routines in case more |
| // memory is needed. |
| // Note: spec indicates that this method *always* returns obj passed in! |
| |
| addElement(item); |
| return item; |
| } |
| |
| /** |
| * Pops an item from the stack and returns it. The item popped is |
| * removed from the Stack |
| * |
| * @returns the Object popped from the stack |
| */ |
| public synchronized Object pop() |
| { |
| if (elementCount == 0) |
| throw new EmptyStackException(); |
| |
| Object obj = elementData[--elementCount]; |
| |
| // Set topmost element to null to assist the gc in cleanup |
| elementData[elementCount] = null; |
| return obj; |
| } |
| |
| /** |
| * Returns the top Object on the stack without removing it |
| * |
| * @returns the top Object on the stack |
| */ |
| public synchronized Object peek() |
| { |
| if (elementCount == 0) |
| throw new EmptyStackException(); |
| |
| return elementData[elementCount - 1]; |
| } |
| |
| /** |
| * Tests if the stack is empty |
| * |
| * @returns true if the stack contains no items, false otherwise |
| */ |
| public boolean empty() |
| { |
| return elementCount == 0; |
| } |
| |
| /** |
| * Returns the position of an Object on the stack, with the top |
| * most Object being at position 1, and each Object deeper in the |
| * stack at depth + 1 |
| * |
| * @param o The object to search for |
| * @returns The 1 based depth of the Object, or -1 if the Object |
| * is not on the stack. |
| */ |
| public synchronized int search(Object o) |
| { |
| for (int i = elementCount-1; i >=0; --i) |
| if (elementData[i].equals(o)) |
| return elementCount - i; |
| |
| return -1; |
| } |
| } |