1 /*
   2  * Copyright (c) 1994, 2006, 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     public static final Class<Boolean> TYPE = Class.getPrimitiveClass("boolean");
  64 
  65     /**
  66      * The value of the Boolean.
  67      *
  68      * @serial
  69      */
  70     private final boolean value;
  71 
  72     /** use serialVersionUID from JDK 1.0.2 for interoperability */
  73     private static final long serialVersionUID = -3665804199014368530L;
  74 
  75     /**
  76      * Allocates a {@code Boolean} object representing the
  77      * {@code value} argument.
  78      *
  79      * <p><b>Note: It is rarely appropriate to use this constructor.
  80      * Unless a <i>new</i> instance is required, the static factory
  81      * {@link #valueOf(boolean)} is generally a better choice. It is
  82      * likely to yield significantly better space and time performance.</b>
  83      *
  84      * @param   value   the value of the {@code Boolean}.
  85      */
  86     public Boolean(boolean value) {
  87         this.value = value;
  88     }
  89 
  90     /**
  91      * Allocates a {@code Boolean} object representing the value
  92      * {@code true} if the string argument is not {@code null}
  93      * and is equal, ignoring case, to the string {@code "true"}.
  94      * Otherwise, allocate a {@code Boolean} object representing the
  95      * value {@code false}. Examples:<p>
  96      * {@code new Boolean("True")} produces a {@code Boolean} object
  97      * that represents {@code true}.<br>
  98      * {@code new Boolean("yes")} produces a {@code Boolean} object
  99      * that represents {@code false}.
 100      *
 101      * @param   s   the string to be converted to a {@code Boolean}.
 102      */
 103     public Boolean(String s) {
 104         this(toBoolean(s));
 105     }
 106 
 107     /**
 108      * Parses the string argument as a boolean.  The {@code boolean}
 109      * returned represents the value {@code true} if the string argument
 110      * is not {@code null} and is equal, ignoring case, to the string
 111      * {@code "true"}. <p>
 112      * Example: {@code Boolean.parseBoolean("True")} returns {@code true}.<br>
 113      * Example: {@code Boolean.parseBoolean("yes")} returns {@code false}.
 114      *
 115      * @param      s   the {@code String} containing the boolean
 116      *                 representation to be parsed
 117      * @return     the boolean represented by the string argument
 118      * @since 1.5
 119      */
 120     public static boolean parseBoolean(String s) {
 121         return toBoolean(s);
 122     }
 123 
 124     /**
 125      * Returns the value of this {@code Boolean} object as a boolean
 126      * primitive.
 127      *
 128      * @return  the primitive {@code boolean} value of this object.
 129      */
 130     public boolean booleanValue() {
 131         return value;
 132     }
 133 
 134     /**
 135      * Returns a {@code Boolean} instance representing the specified
 136      * {@code boolean} value.  If the specified {@code boolean} value
 137      * is {@code true}, this method returns {@code Boolean.TRUE};
 138      * if it is {@code false}, this method returns {@code Boolean.FALSE}.
 139      * If a new {@code Boolean} instance is not required, this method
 140      * should generally be used in preference to the constructor
 141      * {@link #Boolean(boolean)}, as this method is likely to yield
 142      * significantly better space and time performance.
 143      *
 144      * @param  b a boolean value.
 145      * @return a {@code Boolean} instance representing {@code b}.
 146      * @since  1.4
 147      */
 148     public static Boolean valueOf(boolean b) {
 149         return (b ? TRUE : FALSE);
 150     }
 151 
 152     /**
 153      * Returns a {@code Boolean} with a value represented by the
 154      * specified string.  The {@code Boolean} returned represents a
 155      * true value if the string argument is not {@code null}
 156      * and is equal, ignoring case, to the string {@code "true"}.
 157      *
 158      * @param   s   a string.
 159      * @return  the {@code Boolean} value represented by the string.
 160      */
 161     public static Boolean valueOf(String s) {
 162         return toBoolean(s) ? TRUE : FALSE;
 163     }
 164 
 165     /**
 166      * Returns a {@code String} object representing the specified
 167      * boolean.  If the specified boolean is {@code true}, then
 168      * the string {@code "true"} will be returned, otherwise the
 169      * string {@code "false"} will be returned.
 170      *
 171      * @param b the boolean to be converted
 172      * @return the string representation of the specified {@code boolean}
 173      * @since 1.4
 174      */
 175     public static String toString(boolean b) {
 176         return b ? "true" : "false";
 177     }
 178 
 179     /**
 180      * Returns a {@code String} object representing this Boolean's
 181      * value.  If this object represents the value {@code true},
 182      * a string equal to {@code "true"} is returned. Otherwise, a
 183      * string equal to {@code "false"} is returned.
 184      *
 185      * @return  a string representation of this object.
 186      */
 187     public String toString() {
 188         return value ? "true" : "false";
 189     }
 190 
 191     /**
 192      * Returns a hash code for this {@code Boolean} object.
 193      *
 194      * @return  the integer {@code 1231} if this object represents
 195      * {@code true}; returns the integer {@code 1237} if this
 196      * object represents {@code false}.
 197      */
 198     public int hashCode() {
 199         return value ? 1231 : 1237;
 200     }
 201 
 202     /**
 203      * Returns a hash code for a {@code boolean} value; compatible with
 204      * {@code Boolean.hashCode()}.
 205      *
 206      * @since 1.8
 207      *
 208      * @return a hash code value for a {@code boolean} value.
 209      */
 210     public static int hashCode(boolean value) {
 211         return value ? 1231 : 1237;
 212     }
 213 
 214    /**
 215      * Returns {@code true} if and only if the argument is not
 216      * {@code null} and is a {@code Boolean} object that
 217      * represents the same {@code boolean} value as this object.
 218      *
 219      * @param   obj   the object to compare with.
 220      * @return  {@code true} if the Boolean objects represent the
 221      *          same value; {@code false} otherwise.
 222      */
 223     public boolean equals(Object obj) {
 224         if (obj instanceof Boolean) {
 225             return value == ((Boolean)obj).booleanValue();
 226         }
 227         return false;
 228     }
 229 
 230     /**
 231      * Returns {@code true} if and only if the system property
 232      * named by the argument exists and is equal to the string
 233      * {@code "true"}. (Beginning with version 1.0.2 of the
 234      * Java<small><sup>TM</sup></small> platform, the test of
 235      * this string is case insensitive.) A system property is accessible
 236      * through {@code getProperty}, a method defined by the
 237      * {@code System} class.
 238      * <p>
 239      * If there is no property with the specified name, or if the specified
 240      * name is empty or null, then {@code false} is returned.
 241      *
 242      * @param   name   the system property name.
 243      * @return  the {@code boolean} value of the system property.
 244      * @see     java.lang.System#getProperty(java.lang.String)
 245      * @see     java.lang.System#getProperty(java.lang.String, java.lang.String)
 246      */
 247     public static boolean getBoolean(String name) {
 248         boolean result = false;
 249         try {
 250             result = toBoolean(System.getProperty(name));
 251         } catch (IllegalArgumentException e) {
 252         } catch (NullPointerException e) {
 253         }
 254         return result;
 255     }
 256 
 257     /**
 258      * Compares this {@code Boolean} instance with another.
 259      *
 260      * @param   b the {@code Boolean} instance to be compared
 261      * @return  zero if this object represents the same boolean value as the
 262      *          argument; a positive value if this object represents true
 263      *          and the argument represents false; and a negative value if
 264      *          this object represents false and the argument represents true
 265      * @throws  NullPointerException if the argument is {@code null}
 266      * @see     Comparable
 267      * @since  1.5
 268      */
 269     public int compareTo(Boolean b) {
 270         return compare(this.value, b.value);
 271     }
 272 
 273     /**
 274      * Compares two {@code boolean} values.
 275      * The value returned is identical to what would be returned by:
 276      * <pre>
 277      *    Boolean.valueOf(x).compareTo(Boolean.valueOf(y))
 278      * </pre>
 279      *
 280      * @param  x the first {@code boolean} to compare
 281      * @param  y the second {@code boolean} to compare
 282      * @return the value {@code 0} if {@code x == y};
 283      *         a value less than {@code 0} if {@code !x && y}; and
 284      *         a value greater than {@code 0} if {@code x && !y}
 285      * @since 1.7
 286      */
 287     public static int compare(boolean x, boolean y) {
 288         return (x == y) ? 0 : (x ? 1 : -1);
 289     }
 290 
 291     private static boolean toBoolean(String name) {
 292         return ((name != null) && name.equalsIgnoreCase("true"));
 293     }
 294 }