Null point error in Array when trying to give Buttons in array a color

Question

I have an array full of a few buttons and I am trying to go through the array and give each button a color, however I keep getting a null point exception error.

   public static Button[] arrayButtons = new Button[33];                
   @FXML public Button btn1 = new Button();
   @FXML public Button btn2 = new Button();
   @FXML public Button btn3 = new Button();

  @FXML
  public void initializeButtonArray() {        
    arrayButtons[1] = btn1;
    arrayButtons[2] = btn2;
    arrayButtons[3] = btn3;
    arrayButtons[4] = btn4;       
  }

   @FXML
   private void test() {

      initializeButtonArray();
      for(Button btn : arrayButtons) {
          btn.setStyle("-fx-background-color: #FF0000");  //error occurs here
      }
  }

The error occurs when I try to give all the buttons a color inside my for each loop.

You're initializing your Button array to hold 33 objects, but only assigning 4 of them. So the other 29 remain null. Also worth noting is that Java is a zero-indexed language, so the first element in your array is arrayButtons[0], not arrayButtons[1]. And finally, you're doing arrayButtons[4] = btn4, but you never created btn4 in the code you've provided, so this code will never compile as-is. — Jordan
– Jordan, Commented Mar 27, 2019 at 20:39

Matt · Accepted Answer · 2019-03-27 20:50:51Z

2

Arrays Start at 0 so you never set arrayButtons[0] to anything leaving it as null aka waiting to throw a NullPointer when called. You also never initialize btn4 which will throw a null pointer when called and lastly why are you creating a 33 button array when you only initialize 3 the others will throw do you want to guess its a NPE

try this

public static Button[] arrayButtons = new Button[4];

public void initializeButtonArray() {  
    arrayButtons[0] = btn1;      
    arrayButtons[1] = btn2;
    arrayButtons[2] = btn3;
    arrayButtons[3] = btn4;      
}

Add this

@FXML public Button btn4;

On your first iteration through the arrayButtons loop it throws a null pointer because its looking for arrayButtons[0] but its set as null which breaks your whole loop

Also if your referencing a FXML you do not put = new Button();

edited Mar 27, 2019 at 20:50

answered Mar 27, 2019 at 20:38

Matt

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2 Comments

Zurf Over a year ago

omg thank you so much, I'm such a noob at coding ;(, literally spent all day trying to fix this.

fabian Over a year ago

I'd recommend doing arrayButtons = new Button[] { btn1, btn2, btn3, btn4 }; in initializeButtonArray since this way you do not need to change 2 parts of the code when changing the number of elements of the array which decreases possible sources of errors. Also it's shorter...

Aramka · Accepted Answer · 2019-03-27 20:38:38Z

1

You initialized only few elements in array. Other are referencing to null.

Change this line of code

public static Button[] arrayButtons = new Button[33];

to

public static Button[] arrayButtons = new Button[4];

Note that arrays starts at index 0!

answered Mar 27, 2019 at 20:38

Aramka

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