The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
Question: Which classes can an applet extend?
Answer: An applet can extend the java.applet.Applet
class or the java.swing.JApplet
class.
The java.applet.Applet
class extends the java.awt.Panel
class and enables you to use the GUI tools in the AWT package.
The java.swing.JApplet
class is a subclass of java.applet.Applet
that also enables you to use the Swing GUI tools.
Question: For what do you use the start()
method?
Answer: You use the start()
method when the applet must perform a task after it is initialized, before receiving user input. The start()
method either performs the applet's work or (more likely) starts up one or more threads to perform the work.
Question: True or false: An applet can make network connections to any host on the Internet.
Answer: False: An applet can only connect to the host that it came from.
Question: How do you get the value of a parameter specified in the JNLP file from within the applet's code?
Answer: You use the getParameter("Parameter name")
method, which returns the String value of the parameter.
Question: Which class enables applets to interact with JavaScript code in the applet's web page?
Answer: The netscape.javascript.JSObject
class enables applets to interact with JavaScript code in the applet's web page.
Question: True or False: Applets can modify the contents of the parent web page.
Answer: True:Applets can modify the contents of the parent web page by using the getDocument
method of the com.sun.java.browser.plugin2.DOM
class and the Common DOM API.
Exercise: The Exercise
applet's parent web page has a JavaScript variable called memberId
. Write the code to set the value of the memberId
equal to "123489" in the applet's start
method.
Answer:
import java.applet.Applet; import netscape.javascript.*; // add plugin.jar to // classpath during // compilation public class Exercise extends Applet { public void start() { try { JSObject window = JSObject.getWindow(this); window.setMember("memberId", "123489"); } catch (JSException jse) { jse.printStackTrace(); } } }