我不知道怎么了

Question

if(handler.obj.isEmpty())
    handler.addObject(new Box(x, y, ID.Box));
else{
    for(int i = 0; i < handler.obj.size(); i++){
        Object tempObj = handler.obj.get(i);
        if (tempObj.getX() == x && tempObj.getY() == y && tempObj.getId() == ID.Box)
            handler.removeObect(tempObj);
        else
            handler.addObject(new Box(x, y, ID.Box));
    }
}

the handler.addObject() in the else statement seems unreachable or doesn't work

From comment:

public class Handler {
    LinkedList<Object> obj = new LinkedList<Object>();
    public void tick(){
        for (int i = 0; i < obj.size();i++){
            Object tempObj = obj.get(i);
            tempObj.tick();
        }
    }
    public void render(Graphics g){
        for (int i = 0; i < obj.size(); i++){
            Object tempObj = obj.get(i);
            tempObj.render(g);
        }
    }
    public void addObject(Object obj){
        this.obj.add(obj);
    }
    public void removeObect(Object obj){
        this.obj.remove(obj);
    }
}

Answer 1

Let's see. Assume first time it runs, x,y is 1,1 . So you add Box(1,1) .

Next time is run, let's assume x,y is 2,3 . So, enter for loop:

• i = 0 : Not same x,y , so enter else , and add Box(2,3) .
• i = 1 : Same as x,y (yeah, we just added it), so enter if and remove Box(2,3) .

Result: Box added and removed again.

Oh yeah, a debugger would have told you the same thing.

Answer 2

Your problem is that your for loop ends in the wrong place. This causes two undesirable symptoms.

• Firstly, you're adding your new Box once for every element in your list that doesn't match the box, instead of adding it just once.
• Secondly, you're removing some of those new Box objects that you just added, once you get to the end of the loop.

I would recommend rewriting the method like this. Notice how the for loop ends before the new object is added - this makes sure that the object is added at most once. Also notice the return statement after an object is removed - this can be done because once the object is removed, the method has no more work to do.

public void addOrRemoveBox(int x, int y) {
    for(int i = 0; i < handler.obj.size(); i++){
        Object tempObj = handler.obj.get(i);
        if (tempObj.getX() == x && tempObj.getY() == y && tempObj.getId() == ID.Box) {
            handler.removeObect(tempObj);
            return;
         }
    }
    handler.addObject(new Box(x, y, ID.Box));
}

Lastly, you appear to have written your own class called Object (otherwise this code wouldn't compile). This is probably a bad idea, because it will cause you to get confused between your Object class, and the Object class that's built into Java. I suggest you rename that class.