I dont know that much about Serializable, but i need this class to be. How to achieve it?

package helpers;

public class XY implements Comparable<XY>
{
    public int x;
    public int y;

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

    public int compareTo( XY other ) 
    {
        String compare1 = this.x + "-" + this.y;
        String compare2 = other.x + "-" + other.y;

        return compare1.compareTo( compare2 );
    }

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

}

As of now i cant send it as an object with outputstream..I´ve tried just to implement Serializable but it doesnt do the trick!