Question

I am using an Array List to store data about moving objects on screen. I suspect this is because my renderer and my logic are running on separate threads, but sometimes when data is removed from the list I get an indexOutOfBoundsException. I have taken all the steps I can think of to avoid this including try/catch but the exception still sometimes occurs. This is the part of my renderer thread that seems to cause the exception.

public void drawMobs(GL10 gl) {
    boolean playing = MyLaunchActivity.getPlaying();
    if(playing == true){
        try{
             ArrayList<String> mobDat = Play.getMobDat();

        while (currentLoadSpace < mobDat.size()){

        if(!mobDat.isEmpty() || currentLoadSpace < mobDat.size()){

        loadObject = mobDat.get(currentLoadSpace);
        float loadCoordX = Float.parseFloat(mobDat.get(currentLoadSpace + 2));
        float loadCoordY = Float.parseFloat(mobDat.get(currentLoadSpace + 3));

        /*some rendering*/

        currentLoadSpace+=4;
            }
        }
}catch( ArrayIndexOutOfBoundsException e){ Log.d(TAG, "caught");}

    currentLoadSpace = 0;

}}

as you can see I have tried a few things but the error still occurs. Here is the error log

01-02 14:02:42.650: E/AndroidRuntime(6947): FATAL EXCEPTION: GLThread 10
01-02 14:02:42.650: E/AndroidRuntime(6947): java.lang.IndexOutOfBoundsException: Invalid index 23, size is 20
01-02 14:02:42.650: E/AndroidRuntime(6947):     at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:255)
01-02 14:02:42.650: E/AndroidRuntime(6947):     at java.util.ArrayList.get(ArrayList.java:308)
01-02 14:02:42.650: E/AndroidRuntime(6947):     at basicmelon.games.agameofsorts.LoadLevel.drawMobs(LoadLevel.java:530)
01-02 14:02:42.650: E/AndroidRuntime(6947):     at basicmelon.games.agameofsorts.MyGLSurfaceRenderer.onDrawFrame(MyGLSurfaceRenderer.java:82)
01-02 14:02:42.650: E/AndroidRuntime(6947):     at android.opengl.GLSurfaceView$GLThread.guardedRun(GLSurfaceView.java:1429)
01-02 14:02:42.650: E/AndroidRuntime(6947):     at android.opengl.GLSurfaceView$GLThread.run(GLSurfaceView.java:1184)

Answer 1

One possible solution could be:

http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/CopyOnWriteArrayList.html

If this is not an option, you could use synchronized(yourList) {} to prevent concurent modifications.