Having Methods Take Constant Parameters (Java)

Question

Programmers,

I have another question about an exercise in "The Java Programming Language, Fourth Edition" by Ken Arnold, James Gosling, and David Holmes.

Exercise 2.17 reads as follows:

"Add two turn methods to [class] Vehicle: one that takes a number of degrees to turn and one that takes either of the constants Vehicle.TURN_LEFT or Vehicle.TURN_RIGHT."

Is there a way to force a method to only take particular constant parameters? Simply changing the relevant method signatures like so:

public void turn(int degrees)
public void turn(final int degrees)

isn't enough to prevent compile-time errors.

I'd appreciate anyone's input on this question. Thank you.

Peter

Answer 1

If you want to accept only fixed values, then you should create an enum for that:

enum TURN {
LEFT(-30),
RIGHT (30);

private int degree;

private TURN(int degree) {
this.degree = degree;
}

public int getDegree() {
return degree;
}
}

public void turn(TURN t) {
turn(t.getDegree());
}

Answer 2

This was helpful. Thank you!