CODEWITHSUNDEEP
javarecursion
jue78
jue78

Reputation: 47

recursion in java without local variables

I was currently reviewing some code from a colleague and found a use of recursion I have never seen before.

I reduced it, so what he basically does is:

public class Main {
    static class Test {
        private static final int MAX = 10;

        private int mValue = 0;

        void test() {
            System.out.println( mValue );
            mValue++;
            if (mValue < MAX) {
                test();
            }
        }
    }

    public static void main( final String[] args ) {
        final Test test = new Test();
        test.test();
    }
}

When I would use recursion, I would give all needed variables as parameters and then have a return value giving something back, or using one of the parameters to provide a container object where a result could be written in. So that every recursion has it's own scope of data to work on.

I looked around but also every example on the net does it the way I would do it.

So could this lead to any errors? Some inconsistencies in the object? Is there a difference between this and calling different private methods manipulating the member variable?

brgds,

J

Upvotes: 1

Views: 3173

Answers (4)

Eugen Rieck
Eugen Rieck

Reputation: 65274

This will work as expected, as long as a single instance of the Test class never runs .test() concurrently.

Edit

@Itay made me realize, that the word "concurrently" is wrong here - it should be "competingly" in the sense of "not cooperating with or not knowing of each other". I am sorry, the german (my native language) word "Konkurrenz" and the english word "Concurrency" have a slightly different meaning.

/Edit

If this is guaranteed, putting mValue in the class scope, not local scope, can improve locality and cache hit rate, also removes some parameter passing - alltogether it trades some performance gain against encapsulation.

Upvotes: 2

Mik378
Mik378

Reputation: 22171

As long as your logic is thread-safe (immutable object or containing relevant locking), there's no reason to strictly prefer parameter over global class' field even when recursion occurs.

Of course, as long as, the concerned field represents object's state and not a simple ugly helper variable...

Upvotes: 1

Azodious
Azodious

Reputation: 13872

So could this lead to any errors? Some inconsistencies in the object?

In practice, it is not preferred way to implement recursion.

The condition (mValue < MAX) should only be affected within from recursive method. if not, your recursion may end un-expectedly.

Upvotes: 0

Itay Karo
Itay Karo

Reputation: 18286

It could be a problem if the recursive method will be called twice on the same instance?

Upvotes: 0

Related Questions