Is this initialization safe?

Question

I have a class like that:

public class WorkHelper {

    private final Worker worker;

    public WorkHelper(Worker worker) {
        this.worker = worker;
    }

    //...

}

and everybody knows that the initialization below is wrong:

public class Worker {

    private final WorkHelper helper;
    private final SomeClass some;

    public Worker(SomeClass some) {
        helper = new WorkHelper(this);
        this.some = some;
    }

}

But how about the one below? Is this correct?

public class Worker {

    private final WorkHelper helper = new WorkHelper(this);
    private final SomeClass some;

    public Worker(SomeClass some) {
        this.some = some;
    }

}

Why is the second initialization wrong? You can initialize `final` variables in the constructor... — dan1st, Mar 04 '20 at 16:31
"everybody knows that the initialization below is wrong" Really? I don't see what could be wrong there. — Stefan, Mar 04 '20 at 16:32
The problem is passing a partially constructed object to the other class, where some values may not be seen as initialized. There is no difference between 2 and 3 in this respect. — RealSkeptic, Mar 04 '20 at 16:33

Bohemian · Accepted Answer · 2020-03-04T16:47:46.053

4

All versions are unsafe; they are all cases of “letting this escape”.

Consider creating a factory method that creates the worker helper after construction is complete, for example:

public class Worker {

    private WorkHelper helper;
    private SomeClass some;

    // hide the constructor
    private Worker() {}

    public static Worker create(SomeClass some) {
        Worker worker = new Worker();
        worker.some = some;
        worker.helper = new WorkHelper(worker); // pass post construction
        return worker;
    }
}

edited Mar 04 '20 at 16:47

answered Mar 04 '20 at 16:33

Bohemian

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Ok, my fault. :) – dan1st Mar 04 '20 at 16:36
i am new to stackoverflow may someone let me know what is OP – Abhinav Chauhan Mar 04 '20 at 16:44
@RealSkeptic perhaps, but OP has probably simplified his/her real life situation to make the question simple and more broadly useful. – Bohemian Mar 04 '20 at 16:45
@TheGoldy OP == Original Poster (conveniently gender neutral) – Bohemian Mar 04 '20 at 16:45
@Bohemian but why is helper initialized two times? – Life44 Mar 04 '20 at 16:46
@Life44 oops! It got left in from copy-paste. Fixed now. – Bohemian Mar 04 '20 at 16:48
@RealSkeptic as I just posted, that was left there in error due to a sloppy copy paste. Have some sympathy - I am thumbing this code in on my phone and only part of my post is visible at any one time due to tiny screen size. – Bohemian Mar 04 '20 at 16:50

Is this initialization safe?

1 Answers1