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Java Language Reference

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10. The java.lang Package

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The package java.lang contains classes and interfaces that are essential to the Java language. These include:

Because the classes in the java.lang package are so essential, the java.lang package is implicitly imported by every Java source file. In other words, you can refer to all of the classes and interfaces in java.lang using their simple names.

Figure 10.1 shows the class hierarchy for the java.lang package.

Figure 10.1: The java.lang package

[Graphic: Figure 10-1]

Boolean

Name

Boolean

Synopsis

Class Name:

java.lang.Boolean

Superclass:

java.lang.Object

Immediate Subclasses:

None

Interfaces Implemented:

java.io.Serializable

Availability:

JDK 1.0 or later

Description

The Boolean class provides an object wrapper for a boolean value. This is useful when you need to treat a boolean value as an object. For example, there are a number of utility methods that take a reference to an Object as one of their arguments. You cannot specify a boolean value for one of these arguments, but you can provide a reference to a Boolean object that encapsulates the boolean value. Furthermore, as of JDK 1.1, the Boolean class is necessary to support the Reflection API and class literals.

Class Summary

public final class java.lang.Boolean {
    // Constants
    public final static Boolean FALSE;
    public final static Boolean TRUE;
    public final static Class TYPE;                    // New in 1.1
    // Constructors
    public Boolean(boolean value);
    public Boolean(String s);
    // Class Methods
    public static boolean getBoolean(String name);
    public static Boolean valueOf(String s);
    // Instance Methods
    public boolean booleanValue();
    public boolean equals(Object obj);
    public int hashCode();
    public String toString();
}

Constants

TRUE

public static final Boolean TRUE

Description

A constant Boolean object that has the value true.

FALSE

public static final Boolean FALSE

Description

A constant Boolean object that has the value false.

TYPE

public static final Class TYPE

Availability

New as of JDK 1.1

Description

The Class object that represents the type boolean. It is always true that Boolean.TYPE == boolean.class.

Constructors

Boolean

public Boolean(boolean value)

Parameters

value

The boolean value to be made into a Boolean object.

Description

Constructs a Boolean object with the given value.

public Boolean(String s)

Parameters

s

The string to be made into a Boolean object.

Description

Constructs a Boolean object with the value specified by the given string. If the string equals 'true' (ignoring case), the value of the object is true; otherwise it is false.

Class Methods

getBoolean

public static boolean getBoolean(String name)

Parameters

name

The name of a system property.

Returns

The boolean value of the system property.

Description

This methods retrieves the boolean value of a named system property.

valueOf

public static Boolean valueOf(String s)

Parameters

s

The string to be made into a Boolean object.

Returns

A Boolean object with the value specified by the given string.

Description

This method returns a Boolean object with the value true if the string equals "true" (ignoring case); otherwise the value of the object is false.

Instance Methods

booleanValue

public boolean booleanValue()

Returns

The boolean value contained by the object.

equals

public boolean equals(Object obj)

Parameters

obj

The object to be compared with this object.

Returns

true if the objects are equal; false if they are not.

Overrides

Object.equals()

Description

This method returns true if obj is an instance of Boolean, and it contains the same value as the object this method is associated with.

hashCode

public int hashCode()

Returns

A hashcode based on the boolean value of the object.

Overrides

Object.hashCode()

toString

public String toString()

Returns

"true" if the value of the object is true; "false" otherwise.

Overrides

Object.toString()

Description

This method returns a string representation of the Boolean object.

Inherited Methods

Method

Inherited From

Method

Inherited From

clone()

Object

finalize()

Object

getClass()

Object

notify()

Object

notifyAll()

Object

wait()

Object

wait(long)

Object

wait(long, int)

Object

See Also

Boolean Type; Boolean literals; Class; Object; System


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