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Java example source code file (StackImpl.java)

This example Java source code file (StackImpl.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

emptystackexception, object, stackimpl, util

The StackImpl.java Java example source code

/*
 * Copyright (c) 2001, 2003, 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 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;
    }
}

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