java - check an array of objects exist in a list [duplicate]

Question

I have a list of object array in this structure:

List<Object[]> numbers = new ArrayList<>();
numbers.add(new Object[]{1, 2, 3, 4});

I want to check whether an array of objects exist in that list. The contains method always returns false. I use contains in this way:

if(numbers.contains(new Object[]{1,2,3,4}))

This condition always returns false. What's the problem?

new Something() create a new instance so both your new Object[]{1, 2, 3, 4} are differents (not the same hashcode) — user180100
– user180100, Commented Dec 21, 2015 at 6:17
@RC. but the contains method uses equals method to find the matching object — sidgate
– sidgate, Commented Dec 21, 2015 at 6:19
@sidgate - Yes, but for arrays, equals() sin't overriden and hence you will only be checking references — TheLostMind
– TheLostMind, Commented Dec 21, 2015 at 6:20
in that case instead of using List<Object[]> you should use List<List<Object>> — sidgate
– sidgate, Commented Dec 21, 2015 at 6:21

Bahramdun Adil · Accepted Answer · 2015-12-21 06:26:46Z

0

You can try this:

List<Object[]> numbers = new ArrayList<>();
numbers .add(new Object[]{1, 2, 3, 4});
boolean b = list.stream().anyMatch(o -> Arrays.deepEquals(o, new Object[]{1, 2, 3, 4}));

System.out.println("b = " + b);

And the result is:

b = true

edited Dec 21, 2015 at 6:26

answered Dec 21, 2015 at 6:22

Bahramdun Adil

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4 Comments

Makoto Over a year ago

I get the feeling that this question would benefit more from that answer, as a Java 8 option.

Bahramdun Adil Over a year ago

I have checked in my PC, it works well, you can try.

PAA Over a year ago

You should try this, don't use new Operator List<Object[]> numbers = new ArrayList<>(); Object[] obj = new Object[]{1, 2, 3, 4}; numbers.add(obj); if(numbers.contains(obj)) System.out.println("True"); else System.out.println("False");

Makoto Over a year ago

Yes, I know it works. That's probably why I haven't downvoted it. The main point here is that the duplicate question which I've linked to in a response (and subsequently voted to close this question as) would benefit far more from this answer, since first - this is a duplicate question and second - a Java 8 option is indeed missing from the linked dupe.

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