Javascript [Electronic resources] : The Definitive Guide (4th Edition) نسخه متنی

Availability

Netscape 3 LiveConnect

Synopsis

javaclass.static_member // Read or write a static Java field or method
new javaclass(...) // Create a new Java object

Properties

Each JavaClass object contains properties that have the same names as
the public static fields and methods of the Java class it represents.
These properties allow you to read and write the static fields of the
class and invoke the static methods of the class. Each JavaClass
object has different properties; you can use a
for/in loop to enumerate them for any given
JavaClass object.

Description

The JavaClass object is a JavaScript representation of a Java class.
The properties of a JavaClass object represent the public static
fields and methods (sometimes called class fields and class methods)
of the represented class. Note that the JavaClass object does not
have properties representing the

instance fields
of a Java class -- individual instances of a Java class are
represented by the JavaObject object.

The JavaClass object implements the LiveConnect functionality that
allows JavaScript programs to read and write the static variables of
Java classes using normal JavaScript syntax. It also provides the
functionality that allows JavaScript to invoke the static methods of
a Java class.

In addition to allowing JavaScript to read and write Java variable
and method values, the JavaClass object allows JavaScript programs to
create Java objects (represented by a JavaObject object) by using the
new keyword and invoking the constructor method of
a JavaClass.

The data conversion required for communication between JavaScript and
Java through the JavaClass object is handled automatically by
LiveConnect. See Chapter 22 for full details.

Usage

Bear in mind that Java is a

typed language. This
means that each of the fields of an object has a specific data type
that is set to values of only that type. Attempting to set a field to
a value that is not of the correct type results in a JavaScript error
or exception. Attempting to invoke a method with arguments of the
wrong type also causes an error or exception.

Example

java.lang.System is a JavaClass object that
represents the

java.lang.System class in Java.
You can read a static field of this class with code like the
following:

var java_console = java.lang.System.out; 

You can invoke a static method of this class with a line like this
one:

var version = java.lang.System.getProperty("java.version"); 

Finally, the JavaClass object also allows you to create new Java
objects:

var java_date = new java.lang.Date(  ); 

See Also

getClass( ), JavaArray, JavaObject, JavaPackage, the
java property of the Window object; Chapter 22