default java util binary-search returns wrong results [duplicate]

Question

I got very strange behavior from binary search in java util

this code

public static void main (String[] args) throws java.lang.Exception
{
    // your code goes here
     int[] A={-1, 6, 3, 4, 7, 4} ;

     for(int i=0;i<A.length;i++)
     {
         System.out.println(Arrays.binarySearch(A,A[i])+"========="+A[i]);
     }
}

should display all values every element in the array with its index

but it works fine for all elements expect the second one

the returned values are

0=========-1
-5=========6
2=========3
3=========4
4=========7
3=========4

I tested it on java 7 and java 8 and it gave me the same results

you can test online on https://ideone.com/7wMFgG

Are you aware that Binary search works on sorted arrays only? — Luiggi Mendoza
– Luiggi Mendoza, Commented Apr 24, 2015 at 18:23

Eran · Accepted Answer · 2015-04-24 18:24:42Z

4

If you read the Javadoc of binarySearch you'll see that the array must be sorted :

/**
 * Searches the specified array of longs for the specified value using the
 * binary search algorithm.  The array must be sorted (as
 * by the {@link #sort(int[])} method) prior to making this call.  If it
 * is not sorted, the results are undefined.
...

edited Apr 24, 2015 at 18:24

answered Apr 24, 2015 at 18:23

Eran

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