How do I set a final field via a setter?

Question

I have the following abbreviated class:

public class Employee {

    private final float pointPosition;

    public Employee(float pointPosition) {
        this.pointPosition = pointPosition;
    }

}

I'd like to do checks on the pointPosition being passed in by the constuctor, to ensure that it doesn't exceed 1.0.

I tried moving the assignment to it's own private setter method that does a precondition check, but obviously that gave me an error since I'm reassigning a final field outside of the constructor.

I could change the constructor to something like:

public Employee(float newPointPosition) {
    verifyPointPosition(newPointPosition); //Will throw
    this.pointPosition = pointPosition;
}

But I'd prefer to have it all wrapped up neatly in it's own method.

What are my options here?

Answer 1

Option 1: Don't make it final

You could just not make it final and make the setter private.

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Option 2: Do the check and set in the Constructor

That's what you already showed.

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Option 3: The hackish way

You can set final variables with reflection, however i would definitely not recommend this unless you're forced to.

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I'd go with Option 2. If you're worried that your constructor gets too messy, you can just create additional constructors and set them private, for example:

public class MyClass {
    private final float variable;

    public MyClass(float variable) {
        this();
        if(variable < 0.0f || 1.0f < variable)
            throw new IllegalArgumentException("'variable' has to be between 0.0 and 1.0");
        this.variable = variable;
    }

    private MyClass() {
        //Set everything else
    }
}

Actually, this Code will not compile.