for循环中的类方法

Question

I need to draw my buttons in the screen, but when using the for loop enhanced,

public void update(){
  for(Button bt: button){
    bt.update();
  }
}

an error is pointed in the 3rd line (code box above). I don't know what is wrong, neither an alternative way to update/draw the buttons. I tried using the "normal for loop", and the same line is marked.

the console output below:

Exception in thread "Thread-0" java.lang.NullPointerException
    at gameState.FirstScreenState.update(FirstScreenState.java:55)
    at main.GamePanel.update(GamePanel.java:96)
    at main.GamePanel.run(GamePanel.java:71)
    at java.lang.Thread.run(Thread.java:745)

Answer 1

Your button collection/array contains a null .

I strongly recommend renaming button to buttons .