Lesson Three: Putting code into methods.
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Change your class Calculator into:
import java.awt.*;
import java.awt.event.*;
//---------------------------------------------
// Class
//---------------------------------------------
public class Calculator extends Frame {
//---------------------------------------------
// Constructor
//---------------------------------------------
public Calculator() {
initScreen();
System.out.println("Constructing a
new Calculator...");
}
//---------------------------------------------
// Methods
//---------------------------------------------
private void initScreen() {
this.addWindowListener(new
WindowAdapter() {
public void windowClosing(WindowEvent
e) {
System.exit(0); } });
this.setBounds(100, 100, 300, 200);
this.show();
System.out.println("End of the method
initScreen...");
}
}
Save, compile and execute as in the previous lesson.
Nothing new with respect to the last lesson. We merely put some of
the code that was located in the constructor in a method (equivalent to
procedure or subroutine in other languages) and we called this method in
the constructor. It makes it all far more readable.
Reviewing the code:
We added our own method initScreen(). Methods start with a lower-case
letter by convention. Methods and variables can be private, protected or
public. We will go into these identifiers in another lesson later. The
word ´void´ means that the method does not return a value. In one of the
next lessons, we will experiment with this issue.
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