Is there a method in Java that lets you find the index of an element in an int array?

Question

I need to assess the last int in an array where a certain conditional is met. My program can work out what that int is, but it needs to also know where it's position was in the array. I searched on stack-exchange and someone posted this:

Arrays.asList(array).indexOf(indexPos);

As a possible solution, but I am not sure if I am doing it right, because I get the error cannot find symbol. I also allowed:

int test = Arrays.asList(array).indexOf(indexPos);

And then tried to print test, but I could not even get to that point. Thanks.

LexiSort.java:95: error: cannot find symbol int test = Arrays.asList(seq).indexOf(indexPos); That was the error, do I need to import anything? — entropy, Jul 20 '13 at 10:20
...is your array called `array`? Did you import `java.util.Arrays`? You can't just copy/paste code you don't understand and expect it to work automagically. — tckmn, Jul 20 '13 at 10:20
have you declared and assigned indexPos and what is the name of your array.. is it seq? — Aniket Thakur, Jul 20 '13 at 10:26
A binary search may allow you to iterate efficiently to find the index. — , Jul 20 '13 at 10:33
Show us how the array is declared, and paste the exact and complete error message. — JB Nizet, Jul 20 '13 at 10:47

score 1 · Answer 1 · answered Jul 20 '13 at 10:22

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You may need to import java.util.Arrays to get the symbol.

There is no guaranteed way of finding the position of an element in an array except for looping over the array - that is basically what your asList snippets are doing.

This will work as long as your arrays don't have duplicate values. If you need to handle duplicate values, you may need to rethink you data structs.

answered Jul 20 '13 at 10:22

John3136

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I don't have any duplicates, but why am I getting the cannot find symbol error? – entropy Jul 20 '13 at 10:23
@user2396852 see edit re: `import java.util.Arrays` – John3136 Jul 20 '13 at 10:25

score 0 · Answer 2 · edited May 23 '17 at 11:57

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Someone posted a similar question that someone else asked. It seems that this has worked for me.

The Code is:

java.util.Arrays.asList(seq).indexOf(indexPos);

and the Question:Where is Java's Array indexOf?

edited May 23 '17 at 11:57

Community

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answered Jul 20 '13 at 10:26

entropy

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score 0 · Answer 3 · answered Jul 20 '13 at 10:43

Yes you have the method defined in List interface. So you need to use asList() function followed by indexOf() function.

If the array is not sorted you can use java.util.Arrays.asList(theArray).indexOf(o) If the array is sorted, you can make use of a binary search function(improves performance) java.util.Arrays.binarySearch(theArray, o)

As for the error make sure you have imported java.util.Arrays. Also that you have defined Array seq and int indexPos which makes your code int test = Arrays.asList(seq).indexOf(indexPos);.

Is there a method in Java that lets you find the index of an element in an int array?

3 Answers3