View Javadoc
1   /*
2    * Copyright (c) 1994, 2013, 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 java.lang;
27  
28  /**
29   * The Boolean class wraps a value of the primitive type
30   * {@code boolean} in an object. An object of type
31   * {@code Boolean} contains a single field whose type is
32   * {@code boolean}.
33   * <p>
34   * In addition, this class provides many methods for
35   * converting a {@code boolean} to a {@code String} and a
36   * {@code String} to a {@code boolean}, as well as other
37   * constants and methods useful when dealing with a
38   * {@code boolean}.
39   *
40   * @author  Arthur van Hoff
41   * @since   JDK1.0
42   */
43  public final class Boolean implements java.io.Serializable,
44                                        Comparable<Boolean>
45  {
46      /**
47       * The {@code Boolean} object corresponding to the primitive
48       * value {@code true}.
49       */
50      public static final Boolean TRUE = new Boolean(true);
51  
52      /**
53       * The {@code Boolean} object corresponding to the primitive
54       * value {@code false}.
55       */
56      public static final Boolean FALSE = new Boolean(false);
57  
58      /**
59       * The Class object representing the primitive type boolean.
60       *
61       * @since   JDK1.1
62       */
63      @SuppressWarnings("unchecked")
64      public static final Class<Boolean> TYPE = (Class<Boolean>) Class.getPrimitiveClass("boolean");
65  
66      /**
67       * The value of the Boolean.
68       *
69       * @serial
70       */
71      private final boolean value;
72  
73      /** use serialVersionUID from JDK 1.0.2 for interoperability */
74      private static final long serialVersionUID = -3665804199014368530L;
75  
76      /**
77       * Allocates a {@code Boolean} object representing the
78       * {@code value} argument.
79       *
80       * <p><b>Note: It is rarely appropriate to use this constructor.
81       * Unless a <i>new</i> instance is required, the static factory
82       * {@link #valueOf(boolean)} is generally a better choice. It is
83       * likely to yield significantly better space and time performance.</b>
84       *
85       * @param   value   the value of the {@code Boolean}.
86       */
87      public Boolean(boolean value) {
88          this.value = value;
89      }
90  
91      /**
92       * Allocates a {@code Boolean} object representing the value
93       * {@code true} if the string argument is not {@code null}
94       * and is equal, ignoring case, to the string {@code "true"}.
95       * Otherwise, allocate a {@code Boolean} object representing the
96       * value {@code false}. Examples:<p>
97       * {@code new Boolean("True")} produces a {@code Boolean} object
98       * that represents {@code true}.<br>
99       * {@code new Boolean("yes")} produces a {@code Boolean} object
100      * that represents {@code false}.
101      *
102      * @param   s   the string to be converted to a {@code Boolean}.
103      */
104     public Boolean(String s) {
105         this(parseBoolean(s));
106     }
107 
108     /**
109      * Parses the string argument as a boolean.  The {@code boolean}
110      * returned represents the value {@code true} if the string argument
111      * is not {@code null} and is equal, ignoring case, to the string
112      * {@code "true"}. <p>
113      * Example: {@code Boolean.parseBoolean("True")} returns {@code true}.<br>
114      * Example: {@code Boolean.parseBoolean("yes")} returns {@code false}.
115      *
116      * @param      s   the {@code String} containing the boolean
117      *                 representation to be parsed
118      * @return     the boolean represented by the string argument
119      * @since 1.5
120      */
121     public static boolean parseBoolean(String s) {
122         return ((s != null) && s.equalsIgnoreCase("true"));
123     }
124 
125     /**
126      * Returns the value of this {@code Boolean} object as a boolean
127      * primitive.
128      *
129      * @return  the primitive {@code boolean} value of this object.
130      */
131     public boolean booleanValue() {
132         return value;
133     }
134 
135     /**
136      * Returns a {@code Boolean} instance representing the specified
137      * {@code boolean} value.  If the specified {@code boolean} value
138      * is {@code true}, this method returns {@code Boolean.TRUE};
139      * if it is {@code false}, this method returns {@code Boolean.FALSE}.
140      * If a new {@code Boolean} instance is not required, this method
141      * should generally be used in preference to the constructor
142      * {@link #Boolean(boolean)}, as this method is likely to yield
143      * significantly better space and time performance.
144      *
145      * @param  b a boolean value.
146      * @return a {@code Boolean} instance representing {@code b}.
147      * @since  1.4
148      */
149     public static Boolean valueOf(boolean b) {
150         return (b ? TRUE : FALSE);
151     }
152 
153     /**
154      * Returns a {@code Boolean} with a value represented by the
155      * specified string.  The {@code Boolean} returned represents a
156      * true value if the string argument is not {@code null}
157      * and is equal, ignoring case, to the string {@code "true"}.
158      *
159      * @param   s   a string.
160      * @return  the {@code Boolean} value represented by the string.
161      */
162     public static Boolean valueOf(String s) {
163         return parseBoolean(s) ? TRUE : FALSE;
164     }
165 
166     /**
167      * Returns a {@code String} object representing the specified
168      * boolean.  If the specified boolean is {@code true}, then
169      * the string {@code "true"} will be returned, otherwise the
170      * string {@code "false"} will be returned.
171      *
172      * @param b the boolean to be converted
173      * @return the string representation of the specified {@code boolean}
174      * @since 1.4
175      */
176     public static String toString(boolean b) {
177         return b ? "true" : "false";
178     }
179 
180     /**
181      * Returns a {@code String} object representing this Boolean's
182      * value.  If this object represents the value {@code true},
183      * a string equal to {@code "true"} is returned. Otherwise, a
184      * string equal to {@code "false"} is returned.
185      *
186      * @return  a string representation of this object.
187      */
188     public String toString() {
189         return value ? "true" : "false";
190     }
191 
192     /**
193      * Returns a hash code for this {@code Boolean} object.
194      *
195      * @return  the integer {@code 1231} if this object represents
196      * {@code true}; returns the integer {@code 1237} if this
197      * object represents {@code false}.
198      */
199     @Override
200     public int hashCode() {
201         return Boolean.hashCode(value);
202     }
203 
204     /**
205      * Returns a hash code for a {@code boolean} value; compatible with
206      * {@code Boolean.hashCode()}.
207      *
208      * @param value the value to hash
209      * @return a hash code value for a {@code boolean} value.
210      * @since 1.8
211      */
212     public static int hashCode(boolean value) {
213         return value ? 1231 : 1237;
214     }
215 
216    /**
217      * Returns {@code true} if and only if the argument is not
218      * {@code null} and is a {@code Boolean} object that
219      * represents the same {@code boolean} value as this object.
220      *
221      * @param   obj   the object to compare with.
222      * @return  {@code true} if the Boolean objects represent the
223      *          same value; {@code false} otherwise.
224      */
225     public boolean equals(Object obj) {
226         if (obj instanceof Boolean) {
227             return value == ((Boolean)obj).booleanValue();
228         }
229         return false;
230     }
231 
232     /**
233      * Returns {@code true} if and only if the system property
234      * named by the argument exists and is equal to the string
235      * {@code "true"}. (Beginning with version 1.0.2 of the
236      * Java<small><sup>TM</sup></small> platform, the test of
237      * this string is case insensitive.) A system property is accessible
238      * through {@code getProperty}, a method defined by the
239      * {@code System} class.
240      * <p>
241      * If there is no property with the specified name, or if the specified
242      * name is empty or null, then {@code false} is returned.
243      *
244      * @param   name   the system property name.
245      * @return  the {@code boolean} value of the system property.
246      * @throws  SecurityException for the same reasons as
247      *          {@link System#getProperty(String) System.getProperty}
248      * @see     java.lang.System#getProperty(java.lang.String)
249      * @see     java.lang.System#getProperty(java.lang.String, java.lang.String)
250      */
251     public static boolean getBoolean(String name) {
252         boolean result = false;
253         try {
254             result = parseBoolean(System.getProperty(name));
255         } catch (IllegalArgumentException | NullPointerException e) {
256         }
257         return result;
258     }
259 
260     /**
261      * Compares this {@code Boolean} instance with another.
262      *
263      * @param   b the {@code Boolean} instance to be compared
264      * @return  zero if this object represents the same boolean value as the
265      *          argument; a positive value if this object represents true
266      *          and the argument represents false; and a negative value if
267      *          this object represents false and the argument represents true
268      * @throws  NullPointerException if the argument is {@code null}
269      * @see     Comparable
270      * @since  1.5
271      */
272     public int compareTo(Boolean b) {
273         return compare(this.value, b.value);
274     }
275 
276     /**
277      * Compares two {@code boolean} values.
278      * The value returned is identical to what would be returned by:
279      * <pre>
280      *    Boolean.valueOf(x).compareTo(Boolean.valueOf(y))
281      * </pre>
282      *
283      * @param  x the first {@code boolean} to compare
284      * @param  y the second {@code boolean} to compare
285      * @return the value {@code 0} if {@code x == y};
286      *         a value less than {@code 0} if {@code !x && y}; and
287      *         a value greater than {@code 0} if {@code x && !y}
288      * @since 1.7
289      */
290     public static int compare(boolean x, boolean y) {
291         return (x == y) ? 0 : (x ? 1 : -1);
292     }
293 
294     /**
295      * Returns the result of applying the logical AND operator to the
296      * specified {@code boolean} operands.
297      *
298      * @param a the first operand
299      * @param b the second operand
300      * @return the logical AND of {@code a} and {@code b}
301      * @see java.util.function.BinaryOperator
302      * @since 1.8
303      */
304     public static boolean logicalAnd(boolean a, boolean b) {
305         return a && b;
306     }
307 
308     /**
309      * Returns the result of applying the logical OR operator to the
310      * specified {@code boolean} operands.
311      *
312      * @param a the first operand
313      * @param b the second operand
314      * @return the logical OR of {@code a} and {@code b}
315      * @see java.util.function.BinaryOperator
316      * @since 1.8
317      */
318     public static boolean logicalOr(boolean a, boolean b) {
319         return a || b;
320     }
321 
322     /**
323      * Returns the result of applying the logical XOR operator to the
324      * specified {@code boolean} operands.
325      *
326      * @param a the first operand
327      * @param b the second operand
328      * @return  the logical XOR of {@code a} and {@code b}
329      * @see java.util.function.BinaryOperator
330      * @since 1.8
331      */
332     public static boolean logicalXor(boolean a, boolean b) {
333         return a ^ b;
334     }
335 }