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Section One Contents

If, Else And Switch: Basic Control Structures

Java Basics

If, Else And Switch: Basic Control Structures - Con't

The following applet does just that:

//Sourcecode

import java.awt.*; import java.applet.*; public class Project5B extends Applet { int mouseX, mouseY; boolean clicked=false; public boolean mouseDown(Event evt,int x,int y) { clicked=true; mouseX=x; mouseY=y; repaint(); return true; } public void paint(Graphics g) { g.setFont(new Font("Helvetica",Font.PLAIN,15)); g.drawString("Click inside the applet!", 80,50); //we only draw this if the mouse has been clicked once if(clicked) { if(mouseX < size().width/3) g.drawString("You clicked in the left 1/3!",60,100); else if(mouseX > size().width-size().width/3) g.drawString("You clicked in the right 1/3!",60,100); else g.drawString("You clicked in the middle 1/3!",60,100); } } }

In some cases you will want to check for a number of conditions, where a series of if/else statements would be suitable. A more elegant and shorter way is the switch-statement. It tests for a variable (which must be an integer type) to match one of several values. If any of them matches, the body of that statement is executed:

switch(test-expression)
{
   case 0:   body1
      break;
   case 1:   body2
      break;
   case 2:   body3
      break;
   case 3:   body4
      break;
   default:  body5
}

So, if the test-expression equals 0, body1 is executed, if it equals 3, body 4 is executed and if neither of the first four match, the default statement is executed, if any.

The break after each statement takes care of the whole switch-statement being left, then. If none of the single statements matches the value of the test variable, the body of the default-statement is executed. This is mandatory though, you don't have to provide a default branch.

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