Question

Hi i have working code but i would like to print out the coordinates. there is a hashmap that holds Coordinates and Strings. there is a class for Coordinates to allow me to put Coordinates in but when i try to print out it gets confused im clearly not doing something right. Thanks for looking

public class XYTest {
static class Coords {
    int x;
    int y;

    public boolean equals(Object o) {
        Coords c = (Coords) o;
        return c.x == x && c.y == y;
    }

    public Coords(int x, int y) {
        super();
        this.x = x;
        this.y = y;
    }

    public int hashCode() {
        return new Integer(x + "0" + y);
    }
}

public static void main(String args[]) {

    HashMap<Coords, String> map = new HashMap<Coords, String>();

    map.put(new Coords(65, 72), "Dan");

    map.put(new Coords(68, 78), "Amn");
    map.put(new Coords(675, 89), "Ann");

    System.out.println(map.size());
}
}

Answer 1

You have to override toString() in your Coords class.

static class Coords {
    int x;
    int y;

    public boolean equals(Object o) {
        Coords c = (Coords) o;
        return c.x == x && c.y == y;
    }

    public Coords(int x, int y) {
        super();
        this.x = x;
        this.y = y;
    }

    public int hashCode() {
        return new Integer(x + "0" + y);
    }

    public String toString()
    {
        return x + ";" + y;
    }
}

What is confusing you is something like this:

XYTest.Coords@3e25a5

What is this? It is the result of the original toString() method. Here is what it does:

return getClass().getName() + '@' + Integer.toHexString(hashCode());

So, overriding it with your own code will get rid of the confusing output 🙂

---

Please note that your having great hash-collisions. A much better hashCode() implementation would be:

public int hashCode()
{
    return (x << 16) ^ y;
}

To demonstrate your bad hash code: Some collisions:

• (0,101) and (1,1)
• (44,120) and (44012,0)