3 Java Files Problem.

Question

I got 3 java files let say sub.java, sub1.java and sub2.java.
the code for the sub files are as below with
import java.applet.*;
import java.awt.*;
on the top of each files.
sub2.java
=======
public class sub2{
String txt;
int x, y;
void setting(String objStr, int StartX, int StartY){
txt = objStr;
x = StartX;
y = StartY;
public void paint(Graphics g){
g.setColor(Color.blue);
g.drawString(txt, x, y);
sub1.java
=======
public class sub1{
sub2 chair;
String txt;
public void init(){
txt = "Oracle";
chair = new sub2();
public void paint(Graphics g){
chair.setting(txt, 20, 20);
chair.paint(g);
chair.setting(txt, 20, 40);
chair.paint(g);
chair.setting(txt, 20, 60);
chair.paint(g);
sub.java
======
public class sub extends Applet{
sub1 room;
public void init(){
room = new sub1();
public void paint(Graphics g){
room.paint(g);
room.paint(g);
All files can be compiled but i can't run sub.java
where i expect it to paint 6 "Oracle" string.
Anybody can help me?

Answer 1

In your class sub.java, you created a new sub1 object (1) without calling its init() method afterwards.
sub.java
======
public class sub extends Applet{
sub1 room;
public void init(){
(1) room = new sub1();
room.init(); // here is the missing line
Because the init method of sub1 (2) has not been called,
its sub2 instance (chair) won't be created and remains null.
I guess you'll get a NullPointerException at (3) when running the Applet.
sub1.java
=======
public class sub1{
sub2 chair;
String txt;
(2) public void init(){
txt = "Oracle";
chair = new sub2();
public void paint(Graphics g){
chair.setting(txt, 20, 20);(3)
chair.paint(g);
chair.setting(txt, 20, 40);
chair.paint(g);
chair.setting(txt, 20, 60);
chair.paint(g);
I hope this helps...