Availability

Netscape 3 LiveConnect

Synopsis

javaobject.member // Read or write an instance field or method

Properties

Each JavaObject object contains properties that have the same names as the public instance fields and methods (but not the static or class fields and methods) of the Java object it represents. These properties allow you to read and write the value of public fields and invoke the public methods. The properties of a given JavaObject object obviously depend on the type of Java object it represents. You can use the for/in loop to enumerate the properties of any given JavaObject.

Description

The JavaObject object is a JavaScript representation of a Java object. The properties of a JavaObject object represent the public instance fields and public instance methods defined for the Java object. (The class or static fields and methods of the object are represented by the JavaClass object.)

The JavaObject object implements the LiveConnect functionality that allows JavaScript programs to read and write the public instance fields of a Java object using normal JavaScript syntax. It also provides the functionality that allows JavaScript to invoke the methods of a Java object. Data conversion between JavaScript and Java representations 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, and you can set it only to values of that type. For example, the width field of a java.awt.Rectangle object is an integer field, and attempting to set it to a string causes a JavaScript error or exception.

Example

java.awt.Rectangle is a JavaClass that represents the java.awt.Rectangle class. We can create a JavaObject that represents an instance of this class like this:

var r = new java.awt.Rectangle(0,0,4,5); 

We can then read the public instance variables of this JavaObject r with code like this:

var perimeter = 2*r.width + 2*r.height; 

We can also set the value of public instance variables of r using JavaScript syntax:

r.width = perimeter/4;
r.height = perimeter/4; 

See Also

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