java.lang.Boolean 类源码解析

• Boolean源码比较简单。

   public final class Boolean implements java.io.Serializable,
                                         Comparable<Boolean>
   {
       /**
        * The {@code Boolean} object corresponding to the primitive
        * value {@code true}.
        */
       public static final Boolean TRUE = new Boolean(true);
  
       /**
        * The {@code Boolean} object corresponding to the primitive
        * value {@code false}.
        */
       public static final Boolean FALSE = new Boolean(false);
  
       /**
        * The Class object representing the primitive type boolean.
        *
        * @since   JDK1.1
        */
       @SuppressWarnings("unchecked")
       public static final Class<Boolean> TYPE = (Class<Boolean>) Class.getPrimitiveClass("boolean");
  
       /**
        * The value of the Boolean.
        *
        * @serial
        */
       private final boolean value;
  
       /** use serialVersionUID from JDK 1.0.2 for interoperability */
       private static final long serialVersionUID = -3665804199014368530L;
  
       /**
        * Allocates a {@code Boolean} object representing the
        * {@code value} argument.
        *
        * <p><b>Note: It is rarely appropriate to use this constructor.
        * Unless a <i>new</i> instance is required, the static factory
        * {@link #valueOf(boolean)} is generally a better choice. It is
        * likely to yield significantly better space and time performance.</b>
        *
        * @param   value   the value of the {@code Boolean}.
        */
       public Boolean(boolean value) {
           this.value = value;
       }
  
       /**
        * Allocates a {@code Boolean} object representing the value
        * {@code true} if the string argument is not {@code null}
        * and is equal, ignoring case, to the string {@code "true"}.
        * Otherwise, allocate a {@code Boolean} object representing the
        * value {@code false}. Examples:<p>
        * {@code new Boolean("True")} produces a {@code Boolean} object
        * that represents {@code true}.<br>
        * {@code new Boolean("yes")} produces a {@code Boolean} object
        * that represents {@code false}.
        *
        * @param   s   the string to be converted to a {@code Boolean}.
        */
       public Boolean(String s) {
           this(parseBoolean(s));
       }
  
       /**
        * Parses the string argument as a boolean.  The {@code boolean}
        * returned represents the value {@code true} if the string argument
        * is not {@code null} and is equal, ignoring case, to the string
        * {@code "true"}. <p>
        * Example: {@code Boolean.parseBoolean("True")} returns {@code true}.<br>
        * Example: {@code Boolean.parseBoolean("yes")} returns {@code false}.
        *
        * @param      s   the {@code String} containing the boolean
        *                 representation to be parsed
        * @return     the boolean represented by the string argument
        * @since 1.5
        */
       public static boolean parseBoolean(String s) {
           return ((s != null) && s.equalsIgnoreCase("true"));
       }
  
       /**
        * Returns the value of this {@code Boolean} object as a boolean
        * primitive.
        *
        * @return  the primitive {@code boolean} value of this object.
        */
       public boolean booleanValue() {
           return value;
       }
  
       /**
        * Returns a {@code Boolean} instance representing the specified
        * {@code boolean} value.  If the specified {@code boolean} value
        * is {@code true}, this method returns {@code Boolean.TRUE};
        * if it is {@code false}, this method returns {@code Boolean.FALSE}.
        * If a new {@code Boolean} instance is not required, this method
        * should generally be used in preference to the constructor
        * {@link #Boolean(boolean)}, as this method is likely to yield
        * significantly better space and time performance.
        *
        * @param  b a boolean value.
        * @return a {@code Boolean} instance representing {@code b}.
        * @since  1.4
        */
       public static Boolean valueOf(boolean b) {
           return (b ? TRUE : FALSE);
       }
  
       /**
        * Returns a {@code Boolean} with a value represented by the
        * specified string.  The {@code Boolean} returned represents a
        * true value if the string argument is not {@code null}
        * and is equal, ignoring case, to the string {@code "true"}.
        *
        * @param   s   a string.
        * @return  the {@code Boolean} value represented by the string.
        */
       public static Boolean valueOf(String s) {
           return parseBoolean(s) ? TRUE : FALSE;
       }
  
       /**
        * Returns a {@code String} object representing the specified
        * boolean.  If the specified boolean is {@code true}, then
        * the string {@code "true"} will be returned, otherwise the
        * string {@code "false"} will be returned.
        *
        * @param b the boolean to be converted
        * @return the string representation of the specified {@code boolean}
        * @since 1.4
        */
       public static String toString(boolean b) {
           return b ? "true" : "false";
       }
  
       /**
        * Returns a {@code String} object representing this Boolean's
        * value.  If this object represents the value {@code true},
        * a string equal to {@code "true"} is returned. Otherwise, a
        * string equal to {@code "false"} is returned.
        *
        * @return  a string representation of this object.
        */
       public String toString() {
           return value ? "true" : "false";
       }
  
       /**
        * Returns a hash code for this {@code Boolean} object.
        *
        * @return  the integer {@code 1231} if this object represents
        * {@code true}; returns the integer {@code 1237} if this
        * object represents {@code false}.
        */
       @Override
       public int hashCode() {
           return Boolean.hashCode(value);
       }
  
       /**
        * Returns a hash code for a {@code boolean} value; compatible with
        * {@code Boolean.hashCode()}.
        *
        * @param value the value to hash
        * @return a hash code value for a {@code boolean} value.
        * @since 1.8
        */
       public static int hashCode(boolean value) {
           return value ? 1231 : 1237;
       }
  
      /**
        * Returns {@code true} if and only if the argument is not
        * {@code null} and is a {@code Boolean} object that
        * represents the same {@code boolean} value as this object.
        *
        * @param   obj   the object to compare with.
        * @return  {@code true} if the Boolean objects represent the
        *          same value; {@code false} otherwise.
        */
       public boolean equals(Object obj) {
           if (obj instanceof Boolean) {
               return value == ((Boolean)obj).booleanValue();
           }
           return false;
       }
  
       /**
        * Returns {@code true} if and only if the system property
        * named by the argument exists and is equal to the string
        * {@code "true"}. (Beginning with version 1.0.2 of the
        * Java<small><sup>TM</sup></small> platform, the test of
        * this string is case insensitive.) A system property is accessible
        * through {@code getProperty}, a method defined by the
        * {@code System} class.
        * <p>
        * If there is no property with the specified name, or if the specified
        * name is empty or null, then {@code false} is returned.
        *
        * @param   name   the system property name.
        * @return  the {@code boolean} value of the system property.
        * @throws  SecurityException for the same reasons as
        *          {@link System#getProperty(String) System.getProperty}
        * @see     java.lang.System#getProperty(java.lang.String)
        * @see     java.lang.System#getProperty(java.lang.String, java.lang.String)
        */
       public static boolean getBoolean(String name) {
           boolean result = false;
           try {
               result = parseBoolean(System.getProperty(name));
           } catch (IllegalArgumentException | NullPointerException e) {
           }
           return result;
       }
  
       /**
        * Compares this {@code Boolean} instance with another.
        *
        * @param   b the {@code Boolean} instance to be compared
        * @return  zero if this object represents the same boolean value as the
        *          argument; a positive value if this object represents true
        *          and the argument represents false; and a negative value if
        *          this object represents false and the argument represents true
        * @throws  NullPointerException if the argument is {@code null}
        * @see     Comparable
        * @since  1.5
        */
       public int compareTo(Boolean b) {
           return compare(this.value, b.value);
       }
  
       /**
        * Compares two {@code boolean} values.
        * The value returned is identical to what would be returned by:
        * <pre>
        *    Boolean.valueOf(x).compareTo(Boolean.valueOf(y))
        * </pre>
        *
        * @param  x the first {@code boolean} to compare
        * @param  y the second {@code boolean} to compare
        * @return the value {@code 0} if {@code x == y};
        *         a value less than {@code 0} if {@code !x && y}; and
        *         a value greater than {@code 0} if {@code x && !y}
        * @since 1.7
        */
       public static int compare(boolean x, boolean y) {
           return (x == y) ? 0 : (x ? 1 : -1);
       }
  
       /**
        * Returns the result of applying the logical AND operator to the
        * specified {@code boolean} operands.
        *
        * @param a the first operand
        * @param b the second operand
        * @return the logical AND of {@code a} and {@code b}
        * @see java.util.function.BinaryOperator
        * @since 1.8
        */
       public static boolean logicalAnd(boolean a, boolean b) {
           return a && b;
       }
  
       /**
        * Returns the result of applying the logical OR operator to the
        * specified {@code boolean} operands.
        *
        * @param a the first operand
        * @param b the second operand
        * @return the logical OR of {@code a} and {@code b}
        * @see java.util.function.BinaryOperator
        * @since 1.8
        */
       public static boolean logicalOr(boolean a, boolean b) {
           return a || b;
       }
  
       /**
        * Returns the result of applying the logical XOR operator to the
        * specified {@code boolean} operands.
        *
        * @param a the first operand
        * @param b the second operand
        * @return  the logical XOR of {@code a} and {@code b}
        * @see java.util.function.BinaryOperator
        * @since 1.8
        */
       public static boolean logicalXor(boolean a, boolean b) {
           return a ^ b;
       }
   }