CODEWITHSUNDEEP
javaarraylistwhile-loop
Edgar
Edgar

Reputation: 13

Java Array List / while loop counting error

I have the problem that my while loop ends although it only executed once where is my mistake?

public class ear {

    private ArrayList<Point> Master = new ArrayList<Point>();
    private ArrayList<Point> Shot = new ArrayList<Point>();

    public ear() {
        addMaster();
        addShot();
        if (Shot.get(0).y == Master.get(0).y) {
            while (Shot.get(0).x > Master.get(0).x) {
                System.out.println("MasterY: " + Master.get(0).x);
                System.out.println("ShotY: " + Shot.get(0).x);
                moveShot();
            }
        }
    }

    public void moveShot() {
        Point p = new Point();
        for (int i = 0; i < Shot.size(); i++) {
            Shot.get(i).x = p.x;
            p.x -= 10;
            p.y = 5;
            Shot.set(i, p);
        }
    }
}

An object of ear gets created in the main class In move shot i get the shot value x and subtract 10 of it.

Upvotes: 1

Views: 72

Answers (2)

XMB5
XMB5

Reputation: 1612

In the moveShot() method, you create a Point that (by default) is at (0, 0) Then, you iterate through all of your Shots, setting their x value to 0. Then, the x value is no longer greater than your Master x value, so the loop ends

Upvotes: 0

davidxxx
davidxxx

Reputation: 131436

1) this is useless as it is always true:

 if (Shot.get(0).y == Shot.get(0).y)

2) Here Point p = new Point(); Shot.get(i).x = p.x; makes no sense as you assign a new Point to Shot.get(i).x. If you want to have a intermediary value Point to store the current Shot and change its value, you should rather do the contrary :

p.x = Shot.get(i).x - 10;
p.y = Shot.get(i).y + 5;

and then set p as the new value of the current Shot :

 Shot.set(i, p);

3) At last, if x and y are public fields of Shot you could directly change them without using a intermediary Point object:

public void moveShot() { 
    for (int i = 0; i < Shot.size(); i++) {
        Shot.get(i).x -= 10;
        Shot.get(i).y += 5;
    }
}

It is not very advised to have instance public fields but in games it is sometimes used.

Upvotes: 1

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