/*

 * 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

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 */

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;

}