I need to make a life counter so that when my Actor get hit by an Enemy, his life will be decreased by 1.

I put this method in my Actor class:

private void decreaseLife() {
    Actor enemy = getOneIntersectingObject(Enemy.class);
    if (enemy != null) {
        int lastIndex = Scenario.getLifeBar().size()-1;
        Life LastLife = Scenario.getLifeBar().get(lastIndex);
        /** catch error on lastIndex --> "incompatible types" **/



I used Scenario.getLifeBar().size() - 1; to get the last index from my ArrayList collection then decrease it by 1. My LifeMax was set to 3, so when decreased by 1 it should be returning value = 2, and be saved in lastIndex.

This is my code including LifeBar code in Scenario Class:

import greenfoot.*;
import java.util.ArrayList;

public class Scenario extends World {   
    private final int LIFE_MAX = 3; //Max value of my Actor's life
    private static ArrayList LifeBar = new ArrayList();

    public Scenario() {   
        super(600, 400, 1); 

    private void prepare() {     
        prepareLifeBar(40, 30);
        // Add obj. main actor
        // Add obj.enemy

    private void prepareLifeBar(int offsetX, int offsetY) {
        int spaceBetweenLife = 10;  // just to put space between image
        for (int i = 0; i < LIFE_MAX; i++) {
            Life life = new Life();
            life.setLocationX(offsetX+((life.getImage().getWidth()+spaceBetweenLife)*i) );
            addObject(life, life.getLocationX(), life.getLocationY());

    public static ArrayList getLifeBar() {
        return LifeBar;

In my Life class, I put some code to add attributes of LocationX and LocationY to save my Life actor in x and y axis.

I believe there's no other exception caught in any other class related to my life counter, yet my lastIndex caught an incompatible types exception.

What's causing this exception to be thrown?

  • \$\begingroup\$ Hey, welcome to GameDev.SE! I edited your question, but I decided to not add a Greenfoot tag as I don't think that framework is relevant to your issue (I'm happy to be proved wrong though!). \$\endgroup\$ – Alex May 1 '15 at 18:46
  • \$\begingroup\$ @Alex Yes, thanks for editing..! It looks more to the point right now. Actually I was looking for greenfoot-related questions in GameDev before, but found out that it's not yet become tag.. that's why I was suggesting :D \$\endgroup\$ – raisa_ May 1 '15 at 18:53
  • \$\begingroup\$ I see, it's possible that there simply are no questions specifically relating to Greenfoot. If you do have any of your own though, please go ahead and ask them! :) \$\endgroup\$ – Alex May 1 '15 at 18:57

Apparently my arraylist elements stored as Object objects (not as Life objects). So I need to cast the element as type Life first,

I need to change this :

Life LastLife = Scenario.getLifeBar().get(lastIndex);

into this :

Life LastLife =  (Life) SpaceWorld.getLifeBar().get(lastIndex);

and it works just fine.

Check the Reference here

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