boolean.java

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/*
 * @(#)Boolean.java	1.46 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program is free software; you can redistribute it and/or  
 * modify it under the terms of the GNU General Public License version  
 * 2 only, as published by the Free Software Foundation.   
 *   
 * This program is distributed in the hope that it will be useful, but  
 * WITHOUT ANY WARRANTY; without even the implied warranty of  
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU  
 * General Public License version 2 for more details (a copy is  
 * included at /legal/license.txt).   
 *   
 * You should have received a copy of the GNU General Public License  
 * version 2 along with this work; if not, write to the Free Software  
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  
 * 02110-1301 USA   
 *   
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */

package java.lang;

/**
 * The Boolean class wraps a value of the primitive type 
 * <code>boolean</code> in an object. An object of type 
 * <code>Boolean</code> contains a single field whose type is 
 * <code>boolean</code>. 
 * <p>
 * In addition, this class provides many methods for 
 * converting a <code>boolean</code> to a <code>String</code> and a 
 * <code>String</code> to a <code>boolean</code>, as well as other 
 * constants and methods useful when dealing with a 
 * <code>boolean</code>. 
 *
 * @version 1.38, 02/02/00
 * @since   JDK1.0
 */
public final
class Boolean implements java.io.Serializable {
    /** 
     * The <code>Boolean</code> object corresponding to the primitive 
     * value <code>true</code>. 
     */
    public static final Boolean TRUE = new Boolean(true);

    /** 
     * The <code>Boolean</code> object corresponding to the primitive 
     * value <code>false</code>. 
     */
    public static final Boolean FALSE = new Boolean(false);

    /**
     * The Class object representing the primitive type boolean.
     *
     * @since   JDK1.1
     */
    public static final Class	TYPE = Class.getPrimitiveClass("boolean");

    /**
     * The value of the Boolean.
     *
     * @serial
     */
    private boolean value;

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = -3665804199014368530L;

    /**
     * Allocates a <code>Boolean</code> object representing the 
     * <code>value</code> 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</code>.
     */
    public Boolean(boolean value) {
	this.value = value;
    }

    /**
     * Allocates a <code>Boolean</code> object representing the value 
     * <code>true</code> if the string argument is not <code>null</code> 
     * and is equal, ignoring case, to the string <code>"true"</code>. 
     * Otherwise, allocate a <code>Boolean</code> object representing the 
     * value <code>false</code>. Examples:<p>
     * <tt>new&nbsp;Boolean("True")</tt> produces a <tt>Boolean</tt> object 
     * that represents <tt>true</tt>.<br>
     * <tt>new&nbsp;Boolean("yes")</tt> produces a <tt>Boolean</tt> object 
     * that represents <tt>false</tt>.
     *
     * @param   s   the string to be converted to a <code>Boolean</code>.
     */
    public Boolean(String s) {
	this(toBoolean(s));
    }

    /**
     * Returns the value of this <tt>Boolean</tt> object as a boolean 
     * primitive.
     *
     * @return  the primitive <code>boolean</code> value of this object.
     */
    public boolean booleanValue() {
	return value;
    }

    /**
     * Returns a <tt>Boolean</tt> instance representing the specified
     * <tt>boolean</tt> value.  If the specified <tt>boolean</tt> value
     * is <tt>true</tt>, this method returns <tt>Boolean.TRUE</tt>;
     * if it is <tt>false</tt>, this method returns <tt>Boolean.FALSE</tt>.
     * If a new <tt>Boolean</tt> instance is not required, this method
     * should generally be used in preference to the constructor
     * {@link #Boolean(boolean)}, as this method is likely to to yield
     * significantly better space and time performance.
     *
     * @param  b a boolean value.
     * @return a <tt>Boolean</tt> instance representing <tt>b</tt>.
     * @since  1.4
     */
    public static Boolean valueOf(boolean b) {
        return (b ? TRUE : FALSE);
    }

    /**
     * Returns a <code>Boolean</code> with a value represented by the
     * specified String.  The <code>Boolean</code> returned represents the
     * value <code>true</code> if the string argument is not <code>null</code>
     * and is equal, ignoring case, to the string <code>"true"</code>. <p>
     * Example: <tt>Boolean.valueOf("True")</tt> returns <tt>true</tt>.<br>
     * Example: <tt>Boolean.valueOf("yes")</tt> returns <tt>false</tt>.
     *
     * @param   s   a string.
     * @return  the <code>Boolean</code> value represented by the string.
     */
    public static Boolean valueOf(String s) {
	return toBoolean(s) ? TRUE : FALSE;
    }

    /**
     * Returns a <tt>String</tt> object representing the specified
     * boolean.  If the specified boolean is <code>true</code>, then
     * the string <tt>"true"</tt> will be returned, otherwise the
     * string <tt>"false"</tt> will be returned.
     *
     * @param b	the boolean to be converted
     * @return the string representation of the specified <code>boolean</code>
     * @since 1.4
     */
    public static String toString(boolean b) {
        return b ? "true" : "false";
    }

    /**
     * Returns a <tt>String</tt> object representing this Boolean's
     * value.  If this object represents the value <code>true</code>,
     * a string equal to <code>"true"</code> is returned. Otherwise, a
     * string equal to <code>"false"</code> is returned.
     *
     * @return  a string representation of this object. 
     */
    public String toString() {
	return value ? "true" : "false";
    }

    /**
     * Returns a hash code for this <tt>Boolean</tt> object.
     *
     * @return  the integer <tt>1231</tt> if this object represents 
     * <tt>true</tt>; returns the integer <tt>1237</tt> if this 
     * object represents <tt>false</tt>. 
     */
    public int hashCode() {
	return value ? 1231 : 1237;
    }

    /**
     * Returns <code>true</code> if and only if the argument is not 
     * <code>null</code> and is a <code>Boolean </code>object that 
     * represents the same <code>boolean</code> value as this object. 
     *
     * @param   obj   the object to compare with.
     * @return  <code>true</code> if the Boolean objects represent the 
     *          same value; <code>false</code> otherwise.
     */
    public boolean equals(Object obj) {
	if (obj instanceof Boolean) {
	    return value == ((Boolean)obj).booleanValue();
	} 
	return false;
    }

    /**
     * Returns <code>true</code> if and only if the system property 
     * named by the argument exists and is equal to the string 
     * <code>"true"</code>. (Beginning with version 1.0.2 of the 
     * Java<font size="-2"><sup>TM</sup></font> platform, the test of 
     * this string is case insensitive.) A system property is accessible 
     * through <code>getProperty</code>, a method defined by the 
     * <code>System</code> class.
     * <p>
     * If there is no property with the specified name, or if the specified
     * name is empty or null, then <code>false</code> is returned.
     *
     * @param   name   the system property name.
     * @return  the <code>boolean</code> value of the system property.
     * @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 = toBoolean(System.getProperty(name));
        } catch (IllegalArgumentException e) {
        } catch (NullPointerException e) {
        }
        return result;
    }

    private static boolean toBoolean(String name) { 
	return ((name != null) && name.equalsIgnoreCase("true"));
    }
}