Should a java class' final fields always be static?

Question

I could not find any references online about this. But just wanted to know if final fields in a class should always be static or is it just a convention. Based

Answer 1

Absolutely not. Consider:

class Point {
    public final int x;
    public final int y;

    public Point(int _x, int _y) {
        x = _x;
        y = _y;
    }
}

Drop the final, and the class becomes mutable. Add a static, and all your points are the same, and there is no legal way to write the constructor.

Answer 2

Of course not. They must be static if they belong to the class, and not be static if they belong to the instance of the class:

public class ImmutablePerson {
    private static final int MAX_LAST_NAME_LENGTH = 255; // belongs to the type
    private final String firstName; // belongs to the instance
    private final String lastName; // belongs to the instance

    public ImmutablePerson(String firstName, String lastName) {
        if (lastName.length() > MAX_LAST_NAME_LENGTH) {
            throw new IllegalArgumentException("last name too large");
        }
        this.firstName = firstName;
        this.lastName = lastName;
    }

    // getters omitted for brevity
}