Find if a number exists inside of an array in Java

Question

I have an array of account_numbers. I am taking the input from the user and trying to see if the input exists in the array. I've been trying an if statement with a for loop in the parameters, but I feel like that's overkill. Am I missing something?

Ohh! -1 on my question with no comment? Must be on StackOverflow.com — EGHDK, Dec 06 '12 at 04:13
using for loop doesn't look such an overkill to me, you can also use collections like ArrayList for example and use `contains()` method but I think internally it has to apply a single loop (but it'll make your code simpler and compact) — vishal_aim, Dec 06 '12 at 04:16
Similar question here: http://stackoverflow.com/questions/1128723/in-java-how-can-i-test-if-an-array-contains-a-certain-value — tuga, Dec 06 '12 at 04:22
*Do you really think is there a way to identify whether a number exists in an array or not without traversing... All you can do is shorten the syntax but the work will always be the same!!!* — Bharat Sinha, Dec 06 '12 at 05:56
Crazier things have happened. `Arrays.asList(...).contains(...)` works. And I never write the code for traversing through the array. It's just that it doesn't work for int's apparently. — EGHDK, Dec 06 '12 at 18:41

score 4 · Answer 1 · edited Dec 02 '16 at 06:27

4

You can use the Arrays utility class and its simple BinarySearch algorithm:

Arrays.sort(array);  // must sort before next line
boolean found = Arrays.binarySearch(array, someValue) > -1;

edited Dec 02 '16 at 06:27

Tasawar Hussain

650
7
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answered Dec 06 '12 at 04:44

Bohemian

412,405
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score 2 · Answer 2 · answered Dec 06 '12 at 04:23

If you still want to traverse the array without using Lists, you can use this basic structure of for loops:

boolean validInput = false;
for (int i = 0; i < account_numbers.length; i++) {
    if (account_numbers[i] == userInput) {
        validInput = true;
        break;
    }
}

score 1 · Answer 3 · answered Dec 06 '12 at 04:14

1

The simplest way is to convert the array into a list and use contains method as below:

    Long[] account_numbers = new Long[SIZE];//Your existing array

    //get the list from array
    List<Long> accountNumbers = Arrays.asList(account_numbers);

    //check the desired account exist or not
    Long accountToSearch= new Long("12345");
    if(accountNumbers.contains(accountToSearch)){
        //account exist
    }

answered Dec 06 '12 at 04:14

Yogendra Singh

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Hmm... I didn't know about lists. That's awesome. Thanks – EGHDK Dec 06 '12 at 04:17
While that's certainly a very Java thing to do ... all it's going to do internally after wasting time copying the array and creating objects is a simple O(n) linear search which a simple `for` loop would solve. If you're set on using arrays, of course. – Brian Roach Dec 06 '12 at 05:41

score 0 · Answer 4 · answered Aug 25 '18 at 16:55

    Integer arr[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    int a = 7;
    boolean isThere = false;
    List<E> list = new ArrayList<>();
    list.addAll((Collection<? extends E>) Arrays.asList(arr));
              // enter array into the list
    if (list.contains(a)) {
        isThere = true;
    }

    System.out.println(isThere);

Find if a number exists inside of an array in Java

4 Answers4