java - trouble with implementing classes -

i have trouble implementing classes car ship , plane. made interface is:

public interface movable      public void moveforward();     public void moveforward(int x);     public void movebackward();     public void movebackward(int x);     public void moveleft();     public void moveleft(int y);     public void moveright();     public void moveright(int y);     public void displaycoordinates(); 

but want have 2 int fields keep track of coordinates (x, y).

• default coordinates (0, 0), , overloaded constructor allow user initialize them other values.

• movement of objects change coordinates (x, y) 1 step @ time default depending on direction (i.e. moveforward() add 1 x, moveleft() subtract 1 y). overloaded methods allow user change coordinates n number of steps @ time (i.e. moveforward( 7 ) add 7 x). don't know do. can me?

an interface defines methods implementing classes need implement. not define variables or maintain values variables.

for example, might have this:

public interface movable {     public void moveleft(int x); } 

and have class implements interface:

public class ball implements movable {     private int position;      public ball() {         // set initial position         position = 2;     }      @override     public void moveleft(int x) {         position = position - x;     } }