/*

 * 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

 * particular file as subject to the "Classpath" exception as provided

 *

 * 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.

 *

 */

package com.sun.corba.se.impl.orbutil ;

import java.util.EmptyStackException ;

// We implement a Stack here instead of using java.util.Stack because

// java.util.Stack is thread-safe, negatively impacting performance.

// We use an ArrayList instead since it is not thread-safe.

// RequestInfoStack is used quite frequently.

public class StackImpl {

    // The stack for RequestInfo objects.

    private Object[] data = new Object[3] ;

    private int top = -1 ;

    // Tests if this stack is empty.

    public final boolean empty() {

        return top == -1;

    }

    // Looks at the object at the top of this stack without removing it

    // from the stack.

    public final Object peek() {

        if (empty())

            throw new EmptyStackException();

        return data[ top ];

    }

    // Removes the object at the top of this stack and returns that

    // object as the value of this function.

    public final Object pop() {

        Object obj = peek() ;

        data[top] = null ;

        top-- ;

        return obj;

    }

    private void ensure()

    {

        if (top == (data.length-1)) {

            int newSize = 2*data.length ;

            Object[] newData = new Object[ newSize ] ;

            System.arraycopy( data, 0, newData, 0, data.length ) ;

            data = newData ;

        }

    }

    // Pushes an item onto the top of the stack

    public final Object push( Object item ) {

        ensure() ;

        top++ ;

        data[top] = item;

        return item;

    }

}