java.lang.NullPointerException - Help

Im trying to run this code i have written but cannot see whats wrong with it. i get the java.lang.NullPointerException error when running it.

Basically what im trying to do is to move a background x position by using a new method i have created in Dice class (moveBackground).

The code i am running is

di.moveBackground(); where di is the object name

can any one help as i havent got a clue as im new to java

Class Called Dice only part of code is pasted here

Code :

---

private Square background;
 
 public Square getBackground()
   {
      return background;
   }
 
  public void moveBackground()    /** this is what method i am trying to run */
     {
        background.setXPos(75);
      }

---

Square class

Code :

---

 public void setXPos(int x)
   {
      this.xPos = x;
      this.update();
   }

---

Thanks in advance

Is the background variable instantiated prior to calling moveBackground, for example in the constructor or using a setter?

yah i think the object background is not properly instantiated... i think thats the object that the compiler is reffering to..


try to make a constructor that will instantiate the object background as your new object for the square class

Code :

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 public <Class Name> () {
 
         background  = new Square();
 }

---

not sure what you mean all my code is below


To get a dice with 1 spot i run the code:
Square s = new Square();
Circle c1 = new Circle();
Circle c2 = new Circle();
Circle c3 = new Circle();
Circle c4 = new Circle();
Circle c5 = new Circle();
Circle c6 = new Circle();
Circle c7 = new Circle();
Dice di = new Dice(s, c1, c2, c3, c4, c5, c6, c7);

then the idea would be to run:
di.moveBackground();

to move the square created above to the right by 75

You never set or create the background variable. Look at the constructor of the class Dice, there should be something like
background = bg;
or
background = new Square();

Quote:

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Originally Posted by copeg

You never set or create the background variable. Look at the constructor of the class Dice, there should be something like
background = bg;
or
background = new Square();

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brilliant. thanks very much for this

Really appreciate it :)