Java: how to limit argument's values that can be passed to a method

Question

Suppose I have a method that takes one int as a argument,

suppose the method expects only the values 0, 1, 2 and not other int.

Is there a way to "force" the method to accept only 0, 1, 2?

Answer 1

You would have to create a custom data type that can only take the values 0, 1 and 2. You can't use an ordinary int.

In this case you could use an enum:

enum ZeroOneOrTwo {
    ZERO(0),
    ONE(1),
    TWO(2);
    public final int val;
    private ZeroOneOrTwo(int val) {
        this.val = val;
    }
}

and use it as follows:

void myMethod(ZeroOneOrTwo arg) {
    System.out.println("Int value: " + arg.val);
}

If you're forced to take an int as argument (if you're implementing an interface for instance) you can resort to throwing an IllegalArgumentException if the given value is out of range. But generally you would want to let the compiler catch the problem rather than having to deal with it at runtime.

Answer 2

Maybe not applicable in every case (but you didn't specify further what you're trying to accomplish, so maybe it's worth a shot), but maybe you might consider creating three methods instead of one? Or using inheritance, since you're using an OOP language?

For example, instead of coding some information into an int, it might be better coding style to change it.

So instead of ...

void addEmployee(int type) {
    switch(type) {
        case 0: // add regular eymploee
        case 1: // add manager
        case 2: // add CEO
    }
}

... consider this ...

void addRegularEmployee() { 
    // ... 
}
void addManager() { 
    // ... 
}
void addCEO() { 
    // ... 
}

... or even ...

void add(Employee e) {
    // ...
}