Binary Search in Java

There are two ways to do binary search in Java.

1. Arrays.binarysearch() 

Arrays.binarySearch() is the simplest and most efficient method to find an element in a sorted array in Java

Declaration:

public static int binarySearch(data_type arr, data_type key )

where data_type can be any of the primitive data types: byte, char, double, int, float, short, long and Object as well.

return value will be >= 0 if and only if the key is found.

• If input list is not sorted, the results are undefined.
• If there are duplicates, there is no guarantee which one will be found.

Arrays.binarysearch() works for arrays which can be of primitive data type also. Collections.binarysearch() works for objects Collections like ArrayList and LinkedList.

2. Collections.binarysearch() works for objects Collections like ArrayList and LinkedList.

How to implement our own Binary search in Java?

// Java implementation of recursive Binary Search 

class BinarySearch 

{ 

// Returns index of x if it is present in arr[l.. 

// r], else return -1 

int binarySearch(int arr[], int l, int r, int x) 

{ 

if (r>=l) 

{ 

int mid = l + (r - l)/2; 

// If the element is present at the 

// middle itself 

if (arr[mid] == x) 

return mid; 

// If element is smaller than mid, then 

// it can only be present in left subarray 

if (arr[mid] > x) 

return binarySearch(arr, l, mid-1, x); 

// Else the element can only be present 

// in right subarray 

return binarySearch(arr, mid+1, r, x); 

} 

// We reach here when element is not present 

// in array 

return -1; 

} 

// Driver method to test above 

public static void main(String args[]) 

{ 

BinarySearch ob = new BinarySearch(); 

int arr[] = {2,3,4,10,40}; 

int n = arr.length; 

int x = 10; 

int result = ob.binarySearch(arr,0,n-1,x); 

if (result == -1) 

System.out.println("Element not present"); 

else

System.out.println("Element found at index " + 

result); 

} 

}