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LiveConnect

The

JSObject

class has the following methods:

getMember(String name)

— Retrieves a named property of an object. Equivalent to

oObject.property

oObject[“property”]

in JavaScript. The returned value is a Java

Object

getSlot(int index)

— Retrieves a numbered property of an object (mostly for use with

JavaScript arrays). Equivalent to

oObject[index]

. The returned value is a Java

Object

setMember(String name, Object value)

— Sets the value of a named property.

setSlot(int index, Object value)

— Sets the value of a numbered property.

removeMember(String name)

— Removes the value of a named property.

call(String methodName, Object args[])

— Calls the method with the given name and

passes in the arguments contained in the array of

Object

s. The returned value is a Java

Object

eval(String code)

— Evaluates a string of JavaScript code in the context of the object; simi-

lar to JavaScript’s

eval()

function. The returned value is a Java

Object

equals(Object object)

— Determines if the object is equal to another.

One static method for

JSObject,

called

getWindow()

, accepts a Java

Applet

object as an argument

and returns a

JSObject

representation of the JavaScript

window

object.

Using

JSObject

and LiveConnect takes a little getting used to. Suppose you want to retrieve the cur-

rently loaded URL. In JavaScript, this simply requires one line of code:

var sURL = window.location.href

In Java, it becomes a bit more involved:

JSObject window = JSObject.getWindow(this);

JSObject location = (JSObject) window.getMember(“location”);

String sURL = location.getMember(“href”).toString();

The first line gets a reference to the JavaScript

window

object (the argument,

this

, represents the applet

from which the function is being called). The second line retrieves a pointer to the

location

object by

using

getMember()

. Because

getMember()

returns an

Object

, it has to be cast as a

JSObject

in order to

get access to the

JSObject

methods. The last line uses

getMember()

to get the value of

href

, which is

also returned as an

Object

, meaning that

toString()

must be called to get the string value. Obviously,

the Java code for accessing JavaScript objects is a bit verbose, but it gets the job done.

To use LiveConnect in an applet, you must import the package

netscape.javascript

. It’s not neces-

sary to distribute the package with your applet because it is built in to the Java plugin. So, just add the

following line to your

.java

file and begin coding:

import netscape.javascript.*;

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