1 /*
   2  * Copyright (c) 2001, 2003, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package com.sun.corba.se.impl.orbutil ;
  27 
  28 import java.util.EmptyStackException ;
  29 
  30 // We implement a Stack here instead of using java.util.Stack because
  31 // java.util.Stack is thread-safe, negatively impacting performance.
  32 // We use an ArrayList instead since it is not thread-safe.
  33 // RequestInfoStack is used quite frequently.
  34 public class StackImpl {
  35     // The stack for RequestInfo objects.
  36     private Object[] data = new Object[3] ;
  37     private int top = -1 ;
  38 
  39     // Tests if this stack is empty.
  40     public final boolean empty() {
  41         return top == -1;
  42     }
  43 
  44     // Looks at the object at the top of this stack without removing it
  45     // from the stack.
  46     public final Object peek() {
  47         if (empty())
  48             throw new EmptyStackException();
  49 
  50         return data[ top ];
  51     }
  52 
  53     // Removes the object at the top of this stack and returns that
  54     // object as the value of this function.
  55     public final Object pop() {
  56         Object obj = peek() ;
  57         data[top] = null ;
  58         top-- ;
  59         return obj;
  60     }
  61 
  62     private void ensure()
  63     {
  64         if (top == (data.length-1)) {
  65             int newSize = 2*data.length ;
  66             Object[] newData = new Object[ newSize ] ;
  67             System.arraycopy( data, 0, newData, 0, data.length ) ;
  68             data = newData ;
  69         }
  70     }
  71 
  72     // Pushes an item onto the top of the stack
  73     public final Object push( Object item ) {
  74         ensure() ;
  75         top++ ;
  76         data[top] = item;
  77         return item;
  78     }
  79 }