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1 /* |
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2 * Copyright 1994-2005 Sun Microsystems, Inc. All Rights Reserved. |
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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4 * |
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5 * This code is free software; you can redistribute it and/or modify it |
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6 * under the terms of the GNU General Public License version 2 only, as |
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7 * published by the Free Software Foundation. Sun designates this |
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8 * particular file as subject to the "Classpath" exception as provided |
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9 * by Sun in the LICENSE file that accompanied this code. |
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10 * |
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11 * This code is distributed in the hope that it will be useful, but WITHOUT |
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12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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14 * version 2 for more details (a copy is included in the LICENSE file that |
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15 * accompanied this code). |
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16 * |
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17 * You should have received a copy of the GNU General Public License version |
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18 * 2 along with this work; if not, write to the Free Software Foundation, |
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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20 * |
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21 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
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22 * CA 95054 USA or visit www.sun.com if you need additional information or |
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23 * have any questions. |
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24 */ |
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25 |
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26 package java.util; |
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27 |
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28 /** |
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29 * The <code>Stack</code> class represents a last-in-first-out |
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30 * (LIFO) stack of objects. It extends class <tt>Vector</tt> with five |
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31 * operations that allow a vector to be treated as a stack. The usual |
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32 * <tt>push</tt> and <tt>pop</tt> operations are provided, as well as a |
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33 * method to <tt>peek</tt> at the top item on the stack, a method to test |
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34 * for whether the stack is <tt>empty</tt>, and a method to <tt>search</tt> |
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35 * the stack for an item and discover how far it is from the top. |
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36 * <p> |
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37 * When a stack is first created, it contains no items. |
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38 * |
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39 * <p>A more complete and consistent set of LIFO stack operations is |
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40 * provided by the {@link Deque} interface and its implementations, which |
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41 * should be used in preference to this class. For example: |
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42 * <pre> {@code |
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43 * Deque<Integer> stack = new ArrayDeque<Integer>();}</pre> |
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44 * |
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45 * @author Jonathan Payne |
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46 * @since JDK1.0 |
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47 */ |
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48 public |
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49 class Stack<E> extends Vector<E> { |
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50 /** |
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51 * Creates an empty Stack. |
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52 */ |
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53 public Stack() { |
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54 } |
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55 |
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56 /** |
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57 * Pushes an item onto the top of this stack. This has exactly |
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58 * the same effect as: |
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59 * <blockquote><pre> |
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60 * addElement(item)</pre></blockquote> |
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61 * |
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62 * @param item the item to be pushed onto this stack. |
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63 * @return the <code>item</code> argument. |
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64 * @see java.util.Vector#addElement |
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65 */ |
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66 public E push(E item) { |
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67 addElement(item); |
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68 |
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69 return item; |
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70 } |
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71 |
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72 /** |
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73 * Removes the object at the top of this stack and returns that |
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74 * object as the value of this function. |
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75 * |
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76 * @return The object at the top of this stack (the last item |
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77 * of the <tt>Vector</tt> object). |
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78 * @exception EmptyStackException if this stack is empty. |
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79 */ |
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80 public synchronized E pop() { |
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81 E obj; |
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82 int len = size(); |
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83 |
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84 obj = peek(); |
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85 removeElementAt(len - 1); |
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86 |
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87 return obj; |
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88 } |
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89 |
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90 /** |
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91 * Looks at the object at the top of this stack without removing it |
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92 * from the stack. |
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93 * |
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94 * @return the object at the top of this stack (the last item |
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95 * of the <tt>Vector</tt> object). |
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96 * @exception EmptyStackException if this stack is empty. |
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97 */ |
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98 public synchronized E peek() { |
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99 int len = size(); |
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100 |
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101 if (len == 0) |
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102 throw new EmptyStackException(); |
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103 return elementAt(len - 1); |
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104 } |
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105 |
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106 /** |
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107 * Tests if this stack is empty. |
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108 * |
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109 * @return <code>true</code> if and only if this stack contains |
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110 * no items; <code>false</code> otherwise. |
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111 */ |
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112 public boolean empty() { |
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113 return size() == 0; |
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114 } |
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115 |
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116 /** |
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117 * Returns the 1-based position where an object is on this stack. |
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118 * If the object <tt>o</tt> occurs as an item in this stack, this |
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119 * method returns the distance from the top of the stack of the |
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120 * occurrence nearest the top of the stack; the topmost item on the |
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121 * stack is considered to be at distance <tt>1</tt>. The <tt>equals</tt> |
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122 * method is used to compare <tt>o</tt> to the |
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123 * items in this stack. |
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124 * |
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125 * @param o the desired object. |
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126 * @return the 1-based position from the top of the stack where |
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127 * the object is located; the return value <code>-1</code> |
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128 * indicates that the object is not on the stack. |
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129 */ |
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130 public synchronized int search(Object o) { |
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131 int i = lastIndexOf(o); |
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132 |
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133 if (i >= 0) { |
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134 return size() - i; |
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135 } |
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136 return -1; |
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137 } |
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138 |
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139 /** use serialVersionUID from JDK 1.0.2 for interoperability */ |
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140 private static final long serialVersionUID = 1224463164541339165L; |
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141 } |