Constructors using super AND instance variables

I'm learning Java using Sams Teach Yourself Java in 21 days (btw this is taking me much longer than 21 days). In chapter 5, the final exercise asks me to create a class FourDPoint which is a subclass of Point. I did this, but had an interesting result. The first time I did the exercise this was my code:

import java.awt.Point;

class FourDPoint extends Point {
    int x;
    int y;
    int z;
    int t;

    FourDPoint(int x, int y, int z, int t){
        super(x, y);
        this.z = z;
        this.t = t;
    }

    public static void main(String[] arguments){
        FourDPoint fp = new FourDPoint(5, 5, 10, 10);
        System.out.println("x is " + fp.x);
        System.out.println("y is " + fp.y);
        System.out.println("z is " + fp.z);
        System.out.println("t is " + fp.t);
    }
}

The result: x is 0, y is 0, z is 10, y is 10.

I changed my code by eliminating the intitilized x and y, which gave me the correct answer. My question: why did I get x is 0 and y is 0? Do the intitiaized x and y take precedence over the super(x, y)?