Skip to main content

Important Java Question?

Which rules do you have to follow in order to implement an immutable class?

• All fields should be final and private.
• There should be not setter methods.
• The class itself should be declared final in order to prevent subclasses to violate the principle of immutability.
• If fields are not of a primitive type but a reference to another object:
– There should not be a getter method that exposes the reference directly to the caller.
– Don’t change the referenced objects (or at least changing these references is not visisble to clients of the object).

Comments

Popular posts from this blog

What is Servet ?

A servlet is a java class that extends an application hosted on a web server. Handles the HTTP request-response process (for our purposes) Often thought of as an applet that runs on a server. Provides a component base architecture for web development, using the Java Platform The foundation for Java Server Pages (JSP). Alternative to CGI scripting and platform specific server side applications.

What is Applet ?

***What is an Applet? An Applet is a program that can be referenced by an HTML source code of a web page. It is dynamically downloaded from a web server to a browser and it is executed in the environment provided by the browser. Applet Viewer can also be used to execute  the applet. ***FirstApplet.java import java.applet.Applet; import java.awt.Graphics; /*<applet code=“FirstApplet” width=200 height=200> </applet>*/ public class FirstApplet extends Applet { public void paint(Graphics g) { g.drawString(“Hello World”,20,100); } } *** In the above example, The first two line is importing the java.applet and java.awt.Graphics package. The third line is the comment entry which is used only for applet viewer to execute the applet using the HTML source code. The next line declares the FirstApplet class which extends Applet class. Note that each applet created by user must extend the Applet class. There is a paint() method defined...

Example of Check box in AWT

Checkboxes: import java.applet.*; import java.awt.*; import java.awt.event.*; /*<applet code="CheckBoxDemo" width=300 height=300></applet>*/ public class CheckBoxDemo extends Applet implements ItemListener { Label l1; public void init() { Checkbox c1=new Checkbox("B.C.A."); c1.addItemListener(this); add(c1); Checkbox c2=new Checkbox("B.B.A."); c2.addItemListener(this); add(c2); Checkbox c3=new Checkbox("B.Com."); c3.addItemListener(this); add(c3); l1=new Label("                           "); add(l1); } public void itemStateChanged(ItemEvent ie) { Checkbox cb=(Checkbox)ie.getItemSelectable(); l1.setText(cb.getLabel()); } }