Tuesday, June 2, 2009

Java Basics Using Qt Jambi Tutorial

Control Flow

Your code is usually executed from top to bottom. Control flow statements changes the flow of a program depending on a condition. There are 3 control flow statements.

  1. Decision-making statements

    1. if statement


int wheels = 4; //declare and assign wheels to 4.

if (wheels == 4) {

System.out.println(“It is a car”); //executes this if wheel is 4.

}else if (wheels == 2){

System.out.println(“It is a bicycle”); //executes this if wheel is 2.

}else if (wheels == 1){

System.out.println(“It is a unicycle”);// executes this if wheel is 1.


System.out.println(“It is another vehicle”); //executes this if no other conditions are met.


Note: else if and else are optional.

In this example, we used the == equality operator rather than the assignment operator = to test for conditions.

    1. Switch Statements – Switch statement works with:

      1. Primitive data types

      2. Enumerated types

      3. Few classes like Integers, etc.


int wheels = 4;

switch (wheels){

case 1: System.out.println(“unicycle”); break;

case 2: System.out.println(“bicycle”); break;

case 3: System.out.println(“tri-cycle”);break;

case 4: System.out.println(“car”);break;

default: System.out.println(“another vehicle”);


Example of Enumerated Types, Switch Statement

import java.lang.*;

public class enumVehicle{

enum Wheels{

ONE,TWO,FOUR //assign fixed set of constants.


Wheels wheels; //declare wheels variable having Wheels enum.

public enumVehicle(Wheels wheels){ //create constructor

this.wheels = wheels; //initializes variable


public void whatVehicle(){


case ONE: System.out.println("unicycle");break; //prints unicycle since we pass Wheels.ONE to constructor and assign it to wheels.

case TWO: System.out.println("bicycle");break;

case FOUR: System.out.println("car");break;

default: System.out.println("another vehicle");



public static void main(String[] args){

enumVehicle vehicle1 = new enumVehicle(Wheels.ONE); //execute constructor enumVehicle and assign Wheels.ONE to wheels.

vehicle1.whatVehicle(); //call whatVehicle method and print “unicycle.”

enumVehicle vehicle2 = new enumVehicle(Wheels.FOUR); //execute constructor enumVehicle and assign Wheels.FOUR to wheels.

vehicle2.whatVehicle(); //call whatVehicle method and print “car.”



to be continued...

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