CODEWITHSUNDEEP
javarx-java
Alex Kornakov
Alex Kornakov

Reputation: 313

Does it make sense to reuse the same array instead of declaring a new one?

Does it make sense to reuse the same array instead of declaring in .collectInto?

return loadSortedSparseNumbersObservable()
    .collectInto(
            new numbers[1000],
            (array, number) -> {
                int index = computeTrueIndex(...);
                array[index] = number;
            }
    )
    .map(array -> );

We can probably replace the code above with something like:

long[] array = new long[700];
return loadSortedSparseNumbersObservable()
        .doOnNext(
                Arrays.fill(array, 0L),
                (array, number) -> {
                    int index = computeTrueIndex(...);
                    array[index] = number;
                }
        )
        .toCompletable()
        .andThen(Single.just(array))
        .map(array -> );

I don't really like mutating object though.

Upvotes: 3

Views: 117

Answers (2)

Dave Moten
Dave Moten

Reputation: 12097

Your second example has more operators thus potentially more overhead and of course is uglier to read and understand.

The big gotcha in both your examples is that the returned Observable is not reusable safely. Concurrent calls to that same Observable would interact on the array. The safe way to do that is to create a new array for every subscription. Use collect instead of collectInto:

return loadSortedSparseNumbersObservable()
    .collect(
            () -> new numbers[1000],
            (array, number) -> {
                int index = computeTrueIndex(...);
                array[index] = number;
            }
    )
    .map(array -> );

Upvotes: 1

Bryan
Bryan

Reputation: 186

The concern in modifying the array in-place is thread-safety. Arrays in Java are pass-by-reference so any reuse/modification of an array could cause concurrency problems in other parts of a program.

The question, though, doesn't give insight as to the structure or function of the code that is using this particular array, so there may be an application-specific reason to modify in-place. Likewise, there may be a very compelling reason not to.

Upvotes: 0

Related Questions