Map Object Array to Int Array

Question

I'm trying to map and filter my Object[] array to int[] array. Works great, if an object is an int, but throws cast exception if not. I'm wondering if I can somehow attach an try/catch in lambda expression? Here's my code:

b[i] = Arrays.stream(item).mapToInt(e -> (int) e).filter(e -> e % 2 != 0).toArray();

or better way is just to try/catch whole block?

What is expected behaviour, when some objects are ints and other are not? — mishadoff
– mishadoff, Commented Feb 15, 2017 at 10:27
Yeah, of course. Im just wondering how to try/catch that without dropping whole array. — ceroeps
– ceroeps, Commented Feb 15, 2017 at 10:28
either use a filter so that you only map valid objects, or move e -> (int) e into its own method, where you place that try/catch. — Roland
– Roland, Commented Feb 15, 2017 at 10:29
Why would you use try/catch for that? Wouldn't make it so much more sense to use filter to get to find every array item which is a number before trying to convert it? — Tom
– Tom, Commented Feb 15, 2017 at 10:30
It’s become an aside now, but you may use try/catch within your lambda; could be useful in other cases. — Anonymous
– Anonymous, Commented Feb 15, 2017 at 10:58

Eugene · Accepted Answer · 2017-02-15 10:29:30Z

5

Wy not filter objects that are Integers?

.filter(i -> i instanceof Integer).mapToInt(e -> (int) e)

answered Feb 15, 2017 at 10:29

Eugene

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2 Comments

ceroeps Over a year ago

Yeah, why didn't I think of that? Thanks!

tobias_k Over a year ago

Alternatively, without use of lambda: .filter(Integer.class::isInstance) .mapToInt(Integer.class::cast)

Moritz Petersen · Accepted Answer · 2017-02-15 16:24:16Z

3

Use filter() to remove non-numerical values, then convert to Number and call the intValue() method.

int[] ints = Arrays.stream(objects)
    .filter(Number.class::isInstance)
    .map(Number.class::cast)
    .mapToInt(Number::intValue)
    .toArray();

edited Feb 15, 2017 at 16:24

answered Feb 15, 2017 at 10:31

Moritz Petersen

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1 Comment

Holger Over a year ago

Testing with instanceof Number, followed by casting to int is obviously broken. Either, test for instanceof Integer or use .mapToInt(o -> ((Number)o).intValue()). Using .map(o -> (Number) o) .mapToInt(Number::intValue) instead of a single mapToInt creates the impression of an irrational affinity to method references.

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