Question

Well, I’ve a final property but I don’t want to initialize it when I create my object because I can’t. So I tried to not initialize it in my constructor but using a setter, I guessed it would have been something like a only-one-time usable setter, but I’ve this error :

Test.java:27: error: cannot assign a value to final variable foo

    this.foo = new String(foo);

Here is a short code I used to test this :

class Test {

    private final String foo;

    public static void main(String[] args) {
        Test test = new Test();
        test.setFoo("gygygy");
        System.out.println(test.getFoo());
    }

    public Test() {
        System.out.println("Constructor");
    }

    public String getFoo() {
        return foo;
    }

    public void setFoo(String foo) {
        this.foo = foo;
    }

}

So I assume the constructor implicitly makes something like this.foo = new String(); or this.foo = null; and I think I can’t modify this behavior, but how can I have an equivalent to what I wanna do ? I think in something like :

private String foo;

/* ... */

public void setFoo(String foo) {
    if( !(this.foo.isInitialized()) )
        this.foo = foo;
}

but the Object.isInitialized() method obviously doesn’t exist, and I can’t find an equivalent x)

So here’s my question in a few words : How can I do ? I want a final attribute that is not initialized at the instantiation of the object.

Thanks !

Answer 1

You can add a boolean field isInisialized but the best option is to pass the value in the constructor (possibly using a Builder pattern if you need to)