java.lang.Boolean 类源码解析

Posted 2020-10-29 aben-blog

• Boolean源码比较简单。

    1 public final class Boolean implements java.io.Serializable,
    2                                       Comparable<Boolean>
    3 {
    4     /**
    5      * The {@code Boolean} object corresponding to the primitive
    6      * value {@code true}.
    7      */
    8     public static final Boolean TRUE = new Boolean(true);
    9 
   10     /**
   11      * The {@code Boolean} object corresponding to the primitive
   12      * value {@code false}.
   13      */
   14     public static final Boolean FALSE = new Boolean(false);
   15 
   16     /**
   17      * The Class object representing the primitive type boolean.
   18      *
   19      * @since   JDK1.1
   20      */
   21     @SuppressWarnings("unchecked")
   22     public static final Class<Boolean> TYPE = (Class<Boolean>) Class.getPrimitiveClass("boolean");
   23 
   24     /**
   25      * The value of the Boolean.
   26      *
   27      * @serial
   28      */
   29     private final boolean value;
   30 
   31     /** use serialVersionUID from JDK 1.0.2 for interoperability */
   32     private static final long serialVersionUID = -3665804199014368530L;
   33 
   34     /**
   35      * Allocates a {@code Boolean} object representing the
   36      * {@code value} argument.
   37      *
   38      * <p><b>Note: It is rarely appropriate to use this constructor.
   39      * Unless a <i>new</i> instance is required, the static factory
   40      * {@link #valueOf(boolean)} is generally a better choice. It is
   41      * likely to yield significantly better space and time performance.</b>
   42      *
   43      * @param   value   the value of the {@code Boolean}.
   44      */
   45     public Boolean(boolean value) {
   46         this.value = value;
   47     }
   48 
   49     /**
   50      * Allocates a {@code Boolean} object representing the value
   51      * {@code true} if the string argument is not {@code null}
   52      * and is equal, ignoring case, to the string {@code "true"}.
   53      * Otherwise, allocate a {@code Boolean} object representing the
   54      * value {@code false}. Examples:<p>
   55      * {@code new Boolean("True")} produces a {@code Boolean} object
   56      * that represents {@code true}.<br>
   57      * {@code new Boolean("yes")} produces a {@code Boolean} object
   58      * that represents {@code false}.
   59      *
   60      * @param   s   the string to be converted to a {@code Boolean}.
   61      */
   62     public Boolean(String s) {
   63         this(parseBoolean(s));
   64     }
   65 
   66     /**
   67      * Parses the string argument as a boolean.  The {@code boolean}
   68      * returned represents the value {@code true} if the string argument
   69      * is not {@code null} and is equal, ignoring case, to the string
   70      * {@code "true"}. <p>
   71      * Example: {@code Boolean.parseBoolean("True")} returns {@code true}.<br>
   72      * Example: {@code Boolean.parseBoolean("yes")} returns {@code false}.
   73      *
   74      * @param      s   the {@code String} containing the boolean
   75      *                 representation to be parsed
   76      * @return     the boolean represented by the string argument
   77      * @since 1.5
   78      */
   79     public static boolean parseBoolean(String s) {
   80         return ((s != null) && s.equalsIgnoreCase("true"));
   81     }
   82 
   83     /**
   84      * Returns the value of this {@code Boolean} object as a boolean
   85      * primitive.
   86      *
   87      * @return  the primitive {@code boolean} value of this object.
   88      */
   89     public boolean booleanValue() {
   90         return value;
   91     }
   92 
   93     /**
   94      * Returns a {@code Boolean} instance representing the specified
   95      * {@code boolean} value.  If the specified {@code boolean} value
   96      * is {@code true}, this method returns {@code Boolean.TRUE};
   97      * if it is {@code false}, this method returns {@code Boolean.FALSE}.
   98      * If a new {@code Boolean} instance is not required, this method
   99      * should generally be used in preference to the constructor
  100      * {@link #Boolean(boolean)}, as this method is likely to yield
  101      * significantly better space and time performance.
  102      *
  103      * @param  b a boolean value.
  104      * @return a {@code Boolean} instance representing {@code b}.
  105      * @since  1.4
  106      */
  107     public static Boolean valueOf(boolean b) {
  108         return (b ? TRUE : FALSE);
  109     }
  110 
  111     /**
  112      * Returns a {@code Boolean} with a value represented by the
  113      * specified string.  The {@code Boolean} returned represents a
  114      * true value if the string argument is not {@code null}
  115      * and is equal, ignoring case, to the string {@code "true"}.
  116      *
  117      * @param   s   a string.
  118      * @return  the {@code Boolean} value represented by the string.
  119      */
  120     public static Boolean valueOf(String s) {
  121         return parseBoolean(s) ? TRUE : FALSE;
  122     }
  123 
  124     /**
  125      * Returns a {@code String} object representing the specified
  126      * boolean.  If the specified boolean is {@code true}, then
  127      * the string {@code "true"} will be returned, otherwise the
  128      * string {@code "false"} will be returned.
  129      *
  130      * @param b the boolean to be converted
  131      * @return the string representation of the specified {@code boolean}
  132      * @since 1.4
  133      */
  134     public static String toString(boolean b) {
  135         return b ? "true" : "false";
  136     }
  137 
  138     /**
  139      * Returns a {@code String} object representing this Boolean‘s
  140      * value.  If this object represents the value {@code true},
  141      * a string equal to {@code "true"} is returned. Otherwise, a
  142      * string equal to {@code "false"} is returned.
  143      *
  144      * @return  a string representation of this object.
  145      */
  146     public String toString() {
  147         return value ? "true" : "false";
  148     }
  149 
  150     /**
  151      * Returns a hash code for this {@code Boolean} object.
  152      *
  153      * @return  the integer {@code 1231} if this object represents
  154      * {@code true}; returns the integer {@code 1237} if this
  155      * object represents {@code false}.
  156      */
  157     @Override
  158     public int hashCode() {
  159         return Boolean.hashCode(value);
  160     }
  161 
  162     /**
  163      * Returns a hash code for a {@code boolean} value; compatible with
  164      * {@code Boolean.hashCode()}.
  165      *
  166      * @param value the value to hash
  167      * @return a hash code value for a {@code boolean} value.
  168      * @since 1.8
  169      */
  170     public static int hashCode(boolean value) {
  171         return value ? 1231 : 1237;
  172     }
  173 
  174    /**
  175      * Returns {@code true} if and only if the argument is not
  176      * {@code null} and is a {@code Boolean} object that
  177      * represents the same {@code boolean} value as this object.
  178      *
  179      * @param   obj   the object to compare with.
  180      * @return  {@code true} if the Boolean objects represent the
  181      *          same value; {@code false} otherwise.
  182      */
  183     public boolean equals(Object obj) {
  184         if (obj instanceof Boolean) {
  185             return value == ((Boolean)obj).booleanValue();
  186         }
  187         return false;
  188     }
  189 
  190     /**
  191      * Returns {@code true} if and only if the system property
  192      * named by the argument exists and is equal to the string
  193      * {@code "true"}. (Beginning with version 1.0.2 of the
  194      * Java<small><sup>TM</sup></small> platform, the test of
  195      * this string is case insensitive.) A system property is accessible
  196      * through {@code getProperty}, a method defined by the
  197      * {@code System} class.
  198      * <p>
  199      * If there is no property with the specified name, or if the specified
  200      * name is empty or null, then {@code false} is returned.
  201      *
  202      * @param   name   the system property name.
  203      * @return  the {@code boolean} value of the system property.
  204      * @throws  SecurityException for the same reasons as
  205      *          {@link System#getProperty(String) System.getProperty}
  206      * @see     java.lang.System#getProperty(java.lang.String)
  207      * @see     java.lang.System#getProperty(java.lang.String, java.lang.String)
  208      */
  209     public static boolean getBoolean(String name) {
  210         boolean result = false;
  211         try {
  212             result = parseBoolean(System.getProperty(name));
  213         } catch (IllegalArgumentException | NullPointerException e) {
  214         }
  215         return result;
  216     }
  217 
  218     /**
  219      * Compares this {@code Boolean} instance with another.
  220      *
  221      * @param   b the {@code Boolean} instance to be compared
  222      * @return  zero if this object represents the same boolean value as the
  223      *          argument; a positive value if this object represents true
  224      *          and the argument represents false; and a negative value if
  225      *          this object represents false and the argument represents true
  226      * @throws  NullPointerException if the argument is {@code null}
  227      * @see     Comparable
  228      * @since  1.5
  229      */
  230     public int compareTo(Boolean b) {
  231         return compare(this.value, b.value);
  232     }
  233 
  234     /**
  235      * Compares two {@code boolean} values.
  236      * The value returned is identical to what would be returned by:
  237      * <pre>
  238      *    Boolean.valueOf(x).compareTo(Boolean.valueOf(y))
  239      * </pre>
  240      *
  241      * @param  x the first {@code boolean} to compare
  242      * @param  y the second {@code boolean} to compare
  243      * @return the value {@code 0} if {@code x == y};
  244      *         a value less than {@code 0} if {@code !x && y}; and
  245      *         a value greater than {@code 0} if {@code x && !y}
  246      * @since 1.7
  247      */
  248     public static int compare(boolean x, boolean y) {
  249         return (x == y) ? 0 : (x ? 1 : -1);
  250     }
  251 
  252     /**
  253      * Returns the result of applying the logical AND operator to the
  254      * specified {@code boolean} operands.
  255      *
  256      * @param a the first operand
  257      * @param b the second operand
  258      * @return the logical AND of {@code a} and {@code b}
  259      * @see java.util.function.BinaryOperator
  260      * @since 1.8
  261      */
  262     public static boolean logicalAnd(boolean a, boolean b) {
  263         return a && b;
  264     }
  265 
  266     /**
  267      * Returns the result of applying the logical OR operator to the
  268      * specified {@code boolean} operands.
  269      *
  270      * @param a the first operand
  271      * @param b the second operand
  272      * @return the logical OR of {@code a} and {@code b}
  273      * @see java.util.function.BinaryOperator
  274      * @since 1.8
  275      */
  276     public static boolean logicalOr(boolean a, boolean b) {
  277         return a || b;
  278     }
  279 
  280     /**
  281      * Returns the result of applying the logical XOR operator to the
  282      * specified {@code boolean} operands.
  283      *
  284      * @param a the first operand
  285      * @param b the second operand
  286      * @return  the logical XOR of {@code a} and {@code b}
  287      * @see java.util.function.BinaryOperator
  288      * @since 1.8
  289      */
  290     public static boolean logicalXor(boolean a, boolean b) {
  291         return a ^ b;
  292     }
  293 }