142 lines
4.8 KiB
Java
142 lines
4.8 KiB
Java
/*
|
|
* Copyright (c) 1994, 2019, Oracle and/or its affiliates. All rights reserved.
|
|
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
|
|
*
|
|
* This code is free software; you can redistribute it and/or modify it
|
|
* under the terms of the GNU General Public License version 2 only, as
|
|
* published by the Free Software Foundation. Oracle designates this
|
|
* particular file as subject to the "Classpath" exception as provided
|
|
* by Oracle in the LICENSE file that accompanied this code.
|
|
*
|
|
* This code 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
|
|
* version 2 for more details (a copy is included in the LICENSE file that
|
|
* accompanied this code).
|
|
*
|
|
* You should have received a copy of the GNU General Public License version
|
|
* 2 along with this work; if not, write to the Free Software Foundation,
|
|
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
|
|
*
|
|
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
|
|
* or visit www.oracle.com if you need additional information or have any
|
|
* questions.
|
|
*/
|
|
|
|
package java.util;
|
|
|
|
/**
|
|
* The {@code Stack} class represents a last-in-first-out
|
|
* (LIFO) stack of objects. It extends class {@code Vector} with five
|
|
* operations that allow a vector to be treated as a stack. The usual
|
|
* {@code push} and {@code pop} operations are provided, as well as a
|
|
* method to {@code peek} at the top item on the stack, a method to test
|
|
* for whether the stack is {@code empty}, and a method to {@code search}
|
|
* the stack for an item and discover how far it is from the top.
|
|
* <p>
|
|
* When a stack is first created, it contains no items.
|
|
*
|
|
* <p>A more complete and consistent set of LIFO stack operations is
|
|
* provided by the {@link Deque} interface and its implementations, which
|
|
* should be used in preference to this class. For example:
|
|
* <pre> {@code
|
|
* Deque<Integer> stack = new ArrayDeque<Integer>();}</pre>
|
|
*
|
|
* @author Jonathan Payne
|
|
* @since 1.0
|
|
*/
|
|
public class Stack<E> extends Vector<E> {
|
|
/**
|
|
* Creates an empty Stack.
|
|
*/
|
|
public Stack() {
|
|
}
|
|
|
|
/**
|
|
* Pushes an item onto the top of this stack. This has exactly
|
|
* the same effect as:
|
|
* <blockquote><pre>
|
|
* addElement(item)</pre></blockquote>
|
|
*
|
|
* @param item the item to be pushed onto this stack.
|
|
* @return the {@code item} argument.
|
|
* @see java.util.Vector#addElement
|
|
*/
|
|
public E push(E item) {
|
|
addElement(item);
|
|
|
|
return item;
|
|
}
|
|
|
|
/**
|
|
* Removes the object at the top of this stack and returns that
|
|
* object as the value of this function.
|
|
*
|
|
* @return The object at the top of this stack (the last item
|
|
* of the {@code Vector} object).
|
|
* @throws EmptyStackException if this stack is empty.
|
|
*/
|
|
public synchronized E pop() {
|
|
E obj;
|
|
int len = size();
|
|
|
|
obj = peek();
|
|
removeElementAt(len - 1);
|
|
|
|
return obj;
|
|
}
|
|
|
|
/**
|
|
* Looks at the object at the top of this stack without removing it
|
|
* from the stack.
|
|
*
|
|
* @return the object at the top of this stack (the last item
|
|
* of the {@code Vector} object).
|
|
* @throws EmptyStackException if this stack is empty.
|
|
*/
|
|
public synchronized E peek() {
|
|
int len = size();
|
|
|
|
if (len == 0)
|
|
throw new EmptyStackException();
|
|
return elementAt(len - 1);
|
|
}
|
|
|
|
/**
|
|
* Tests if this stack is empty.
|
|
*
|
|
* @return {@code true} if and only if this stack contains
|
|
* no items; {@code false} otherwise.
|
|
*/
|
|
public boolean empty() {
|
|
return size() == 0;
|
|
}
|
|
|
|
/**
|
|
* Returns the 1-based position where an object is on this stack.
|
|
* If the object {@code o} occurs as an item in this stack, this
|
|
* method returns the distance from the top of the stack of the
|
|
* occurrence nearest the top of the stack; the topmost item on the
|
|
* stack is considered to be at distance {@code 1}. The {@code equals}
|
|
* method is used to compare {@code o} to the
|
|
* items in this stack.
|
|
*
|
|
* @param o the desired object.
|
|
* @return the 1-based position from the top of the stack where
|
|
* the object is located; the return value {@code -1}
|
|
* indicates that the object is not on the stack.
|
|
*/
|
|
public synchronized int search(Object o) {
|
|
int i = lastIndexOf(o);
|
|
|
|
if (i >= 0) {
|
|
return size() - i;
|
|
}
|
|
return -1;
|
|
}
|
|
|
|
/** use serialVersionUID from JDK 1.0.2 for interoperability */
|
|
@java.io.Serial
|
|
private static final long serialVersionUID = 1224463164541339165L;
|
|
}
|