Application & JApplet - Inner Classes

Question

Hi,
I am having problems understanding the purpose of Inner Classes.
1. Is purpose of inner class in an Application to take care of what init method
takes care of in a JApplet. I believe init method in JApplet brings up the browser and
xecutes statements in init()?
2. Is it possible to write the enclosed Application without using an Inner Class?
If so, can someone please show me how?
3. Is it possible to write the enclosed JApplet using an inner Class?
If so, can someone please show me how?
Maybe if I see how an Application and JApplet are written with and without inner classes, this may help me understand.
Thank you.
//APPLICATION USING AN INNER CLASS
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
//outerclass
public class InnerTest extends JFrame
private JTextField numField, sumField;
private int sum = 0;
public InnerTest()
super("Inner Test");
Container c = getContentPane();
c.setLayout(new FlowLayout());
ActionEventHandler handler = new ActionEventHandler();
numField = new JTextField(10);
sumField = new JTextField(10);
numField.addActionListener(handler);
c.add(numField);
c.add(sumField);
public static void main(String args[])
InnerTest win = new InnerTest();
win.setSize(400, 140);
win.show();
//Innerclass
private class ActionEventHandler implements ActionListener
public void actionPerformed(ActionEvent e)
sum += Integer.parseInt(numField.getText()); // access to sum and numField
numField.setText("");
sumField.setText(Integer.toString(sum));
JAPPLET
Below is modification of above code to a JApplet
without using inner class. I have CAPITALIZED MODIFICATIONS.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class InnerTest extends JAPPLET
private JTextField numField, sumField;
private int sum = 0;
public VOID INIT()
super("Inner Test");
Container c = getContentPane();
c.setLayout(new FlowLayout());
ActionEventHandler handler = new ActionEventHandler();
numField = new JTextField(10);
sumField = new JTextField(10);
numField.addActionListener(THIS);
c.add(numField);
c.add(sumField);
public void actionPerformed(ActionEvent e)
sum += Integer.parseInt(numField.getText()); // access to sum and numField
numField.setText("");
sumField.setText(Integer.toString(sum));

Answer 1

1. Is purpose of inner class in an Application to
take care of what init method
takes care of in a JApplet. I believe init method in
JApplet brings up the browser and
xecutes statements in init()?No. The init() method of an applet is similar to the constructor for an application. It is used to initialize data for the applet, the same data you will initialize in the constructor of the application.
>
2. Is it possible to write the enclosed Application
without using an Inner Class?Yes it is possible. The power of an inner class is that is has access even to private member variables of the enclosing class. In your case the event handler has access to the private variables: numField and sumField. If you do not use an inner class you have to pass a reference to your frame in the event handler's constructor and access the variables through that reference. But in this case you do not have access to private variables. So you must provide methods to access those variables or you must change theri visibility.
ActionEventHandler handler = new ActionEventHandler(this);Provide accessor methods in InnerTest class:
public String getTextString(){
     return numField.getText();
public void setTextString(String text){
     numField.setText(text);
}As for the applet it works just as your application in this case, you can use inner classes or not but with the same restrictions.
I hope you can understand what I tried to explain.