user2821023 user2821023 - 1 year ago 97
Java Question

Java8 using enum values in interface's default methods

I'm exploring possibilities of static and default methods introduced in java 8.

I've an interface that has 2 default methods that do construct a command, that I run on server through ssh to do some simple tasks remotely. Moving mouse requires 2 arguments: x and y position of the mouse.

public interface Robot {

default String moveMouse(int x, int y) {
return constructCmd("java -jar move_mouse.jar " + x + " " + y);

default String clickLeft() {
return constructCmd("java -jar click_left.jar");

static String constructCmd(String cmd) {
return "export DISPLAY=:1.0\n" +
"cd Desktop\n" +

I've multiple enums with values preset, I could potently combine all enums into one and not use interface what so ever, however that enum would contain hundreds or thousands of values and I want to keep it somewhat organised, so I've split evertying in multiple enums.

I want all enums to share same methods so I figured I'll give default methods in an interface a shot.

public enum Field implements Robot {

AGE_FIELD(778, 232),

NAME_FIELD(662, 280);

public int x;
public int y;

Field(int x, int y) {
this.x = x;
this.y = y;

So I can get String commands by:

Field.AGE_FIELD.moveMouse(Field.AGE_FIELD.x, Field.AGE_FIELD.y);

However moveMouse looks really bad to me and I think it should be somehow possible to use enum's values by default.

Anyone has a a nice solution for such problem?

Answer Source

The problem is your architecture. On the one hand, you have a layer that actually executes the mouse-movement (represented by your Robot interface). Now, you need a layer that produces mouse-movement and sends it to a Robot to execute this mouse-movement. Let's call the interface defining this layer MouseTarget (fits your example nicely):

public interface MouseTarget
    public int getTargetX();
    public int getTargetY();

    public default void moveMouseHere(Robot robot) {
        robot.moveMouse(this.getTargetX(), this.getTargetY());

This interface represents one mouse-movement to one target. As you see the moveMouseHere(Robot robot) method expects a Robot to send the movement to (which does the actual work). Now, all what is left is to adapt your Fields enum:

public enum Fields implements MouseTarget {

    AGE_FIELD(778, 232), NAME_FIELD(662, 280);

    public int targetX;
    public int targetY;

    Fields(int targetX, int targetY) {
        this.targetX = targetX;
        this.targetY = targetY;

    public int getTargetX()
        return (this.targetX);

    public int getTargetY()
        return (this.targetY);
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