For the HTML syntax for applets and plug-ins, see "Applet" or "Plugin".
public void init() {
System.out.println("Hello, world!")
}
java_30 file that includes the following Java packages:
java_30 contains the following netscape packages:
In addition, java_30 contains some other netscape packages:
java_30 file is delivered in the Programjavaclasses directory beneath the Navigator directory. To access the packages in java_30, place the file in the classpath of the JDK compiler in either of the following ways:
CLASSPATH environment variable to specify the directory path where java_30 is installed.
java_30 when you compile by using the -classpath command line parameter.
CLASSPATH with a value similar to the following:
C:Program FilesNetscapeNavigatorProgramjavaclassesSee the Sun JDK documentation for more information about CLASSPATH.
System.out.println to display a message on the Java Console.
In JavaScript, Java packages and classes are properties of the Packages object. Use Java syntax to reference Java objects in JavaScript, with the name of the Packages object optionally prepended:
[Packages.]packageName.className.methodNameThe name
Packages is optional for java, sun, and netscape packages; in code, java, sun, and netscape are aliases for Packages.java, Packages.sun, and Packages.netscape. For example, you can refer to the Java class java.lang.System as either Packages.java.lang.System or as java.lang.System in your code. The name Packages is required for other packages.
Access fields and methods in a class with the same syntax that you use in Java. For example, the following JavaScript code prints a message to the Java Console:
var System = java.lang.SystemThe first line in this example makes the JavaScript variable System refer to the class java.lang.System. The second line invokes the println method of the static variable err in the Java System class. Because println expects a java.lang.String argument, the JavaScript string is converted to a java.lang.String automatically. You can even use Java class constructors in JavaScript. For example, the following code creates a Java Date object.
System.err.println("Greetings from JavaScript")
var mydate = new java.util.Date()
document.appletName, where appletName is the value of the NAME attribute of the APPLET tag. There is also an applets array that contains all the applets in a page; you can reference elements of the array through the applet name (as in an associative array) or by the ordinal number of the applet on the page (starting from zero).
For example, consider the basic "Hello World" applet in Java:
import java.applet.Applet;The following HTML runs and displays the applet, and names it "HelloWorld" (with the NAME attribute):
import java.awt.Graphics;
public class HelloWorld extends Applet {
public void paint(Graphics g) {
g.drawString("Hello world!", 50, 25);
}
}
<APPLET CODE="HelloWorld.class" NAME="HelloWorld" WIDTH=150 HEIGHT=25>You can reference this applet in JavaScript in either of the following ways:
</APPLET>
document.HelloWorldIf this is the first applet in the document (topmost on the page), you could also reference it as:
document.applets["HelloWorld"]
document.applets[0]The applets array has a length property,
document.applets.length, that indicates the number of applets in the document.
All public variables declared in an applet, and its ancestor classes and packages are available in JavaScript. Static methods and properties declared in an applet are available to JavaScript as methods and properties of the Applet object. You can get and set property values, and you can call methods that return string, numeric, and boolean values.
java.awt.Component).
import java.applet.Applet;Making the message string a variable allows you to modify it from JavaScript. Now modify the HTML file as follows:
import java.awt.Graphics;
public class HelloWorld extends Applet {
String myString;
public void init() {
myString = new String("Hello, world!");
}
public void paint(Graphics g) {
g.drawString(myString, 25, 20);
}
public void setString(String aString) {
myString = aString;
repaint();
}
}
<APPLET CODE="HelloWorld1.class" NAME="Hello" WIDTH=150 HEIGHT=25>When you compile the HelloWorld applet, and load the HTML page into Navigator, you initially see "Hello, World!" displayed in the gray applet panel. However, you can now change it by entering text in the text field and clicking on the button. This demonstrates controlling an applet from JavaScript.
</APPLET>
<FORM NAME="form1">
<INPUT TYPE="button" VALUE="Set String"
onClick="document.HelloWorld.setString(document.form1.str.value)">
<BR>
<INPUT TYPE="text" SIZE="20" NAME="str">
</FORM>
<EMBED SRC=myavi.avi WIDTH=320 HEIGHT=200>If this HTML defines the first plug-in in a document, you can use the following code to access it:
document.embeds[0]If the plug-in is associated with the Java class netscape.plugin.Plugin, you can access its static variables and methods the way you access an applet's variables and methods. The embeds array has a length property,
document.embeds.length, that indicates the number of plug-ins embedded in the document. See "Determining installed plug-ins" for more information about plug-ins.
import netscape.javascript.*The package netscape.javascript defines the JSObject class and the JSException exception object. The author of an HTML page must permit an applet to access JavaScript by specifying the MAYSCRIPT attribute of the APPLET tag. This prevents an applet from accessing JavaScript on a page without the knowledge of the page author. Attempting to access JavaScript from an applet that does not have the MAYSCRIPT attribute generates an exception.
public void init() {
JSObject win = JSObject.getWindow(this);
}
public void init() {
win = JSObject.getWindow(this);
JSObject doc = (JSObject) win.getMember("document");
JSObject myForm = (JSObject) doc.getMember("testForm");
}
Notice that JavaScript objects appear as instances of the class netscape.javascript.JSObject in Java. Values passed between Java to JavaScript are converted as described in "netscape.javascript.JSObject".
If the JavaScript object document.testForm.jazz is a checkbox, the following code allows you to access its checked property:
public void init() {
win = JSObject.getWindow(this);
JSObject doc = (JSObject) win.getMember("document");
JSObject myForm = (JSObject) doc.getMember("testForm");
JSObject check = (JSObject) myForm.getMember("jazz");
Boolean isChecked = (Boolean) check.getMember("checked");
} Calling JavaScript methods
The call and eval methods of the class netscape.javascript.JSObject enable you to call JavaScript methods. Use getWindow to get a handle for the JavaScript window, then use call or eval to access a JavaScript method.
Use either of the following syntaxes to call JavaScript methods:
1. JSObject.getWindow().call("methodName", arguments)
In the first form of this syntax, methodName is the name of the JavaScript method you want to call, and arguments is an array of arguments to pass to the JavaScript method. In the second form of the syntax, expression is a JavaScript expression that evaluates to a JavaScript method.
2. JSObject.getWindow().eval("expression") Example: Hello World
Returning to the HelloWorld example, modify the paint method so that it calls the JavaScript alert method (with the message "Painting!") as follows:
public void paint(Graphics g) {
Then add the MAYSCRIPT attribute to the APPLET tag in the HTML page, recompile the applet, and try it. Each time the applet is painted (when it is initalized, when you enter a new text value, and when the page is reloaded) a JavaScript alert box pops up. This is a simple illustration of calling JavaScript from Java.
g.drawString(myString, 25, 20);
JSObject win = JSObject.getWindow(this);
String args[] = {"Painting!"};
win.call("alert", args);
}Note
You may have to reload the HTML page by choosing File | Open File... instead
of clicking on the reload button, to ensure that the applet is re-initialized.
You can also call user-defined functions from a Java applet. For example, add the following function to the HEAD of the HTML page with the HelloWorld applet:
<SCRIPT>
This simple function pops up an alert dialog box displaying the name and version of the client software being used. Then modify the init method similarly to the way you modified paint:
function test() {
alert("You are using " + navigator.appName + " " + navigator.appVersion)
}
</SCRIPT>public void init() {
Notice that args2 is declared as an array with no elements, even though the method does not take any arguments. When you recompile the applet and reload the HTML page (and re-initialize the applet), a JavaScript alert dialog box will pop up displaying the version of Navigator you are running. This is a simple illustration of calling a user-defined function from Java.
myString = new String("Hello, world!")
JSObject win = JSObject.getWindow(this)
String args2[] = {""}
win.call("test", args2)
}