How to find the index of an element in an int array?

Question

How can I find an index of a certain value in a Java array of type int?

I tried using Arrays.binarySearch on my unsorted array, it only som

Answer 1

You could convert it to a list, then use the indexOf method:

Array.asList(array).indexOf(1); 

http://download.oracle.com/javase/1.5.0/docs/api/java/util/Arrays.html#asList(T...) http://download.oracle.com/javase/1.5.0/docs/api/java/util/List.html#indexOf(java.lang.Object)

Answer 2

You can either walk through the array until you find the index you're looking for, or use a List instead. Note that you can transform the array into a list with asList().

Answer 3

Another option if you are using Guava Collections is Ints.indexOf

// Perfect storm:
final int needle = 42;
final int[] haystack = [1, 2, 3, 42];

// Spoiler alert: index == 3
final int index = Ints.indexOf(haystack, needle);

This is a great choice when space, time and code reuse are at a premium. It is also very terse.

Answer 4

You need to sort values before using binary search. Otherwise, the manual way is to try all ints in your tab.

public int getIndexOf( int toSearch, int[] tab )
{
  for( int i=0; i< tab.length ; i ++ )
    if( tab[ i ] == toSearch)
     return i;

  return -1;
}//met

An alternative method could be to map all index for each value in a map.

tab[ index ] = value;
if( map.get( value) == null || map.get( value) > index )
    map.put( value, index );

and then map.get(value) to get the index.

Regards, Stéphane

@pst, thanks for your comments. Can you post an other alternative method ?

Answer 5

A look at the API and it says you have to sort the array first

So:

Arrays.sort(array);
Arrays.binarySearch(array, value);

If you don't want to sort the array:

public int find(double[] array, double value) {
    for(int i=0; i<array.length; i++) 
         if(array[i] == value)
             return i;
}

Answer 6

Simple:

public int getArrayIndex(int[] arr,int value) {
    for(int i=0;i<arr.length;i++)
        if(arr[i]==value) return i;
    return -1;
}