what is binary search used for code example

Example: binary search

//Binary search can apply to sorted data only.
//Time complexity of binary search is O(log n ).
//It always divide the whole data in parts and compare  a search key to middle element only.


import java.util.*;
public class BinarySearch {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		int[] a = {10,20,50,30,40};
		int key=sc.nextInt();
		
		Arrays.sort(a);					// An method in java.util.Arrays package to sort an array element.
		
		int first=0,end=a.length-1,mid=0,flag=0;

		while(first<=end)
		{
			mid=(first+end)/2;
			if(key<a[mid])				// Move to left part if key is smaller than middle element.
			{
				end = mid-1;
			}
			else if(key>a[mid])		   // Move to right part if key is greater than middle element.
			{
				first = mid+1;
			}
			else
			{
				flag=1;
				break;
			}
		}
		if(flag==1)
		{
			System.out.println("Success! found");
		}
		else
		{
			System.out.println("Error! This key (" + key + ") does not exist in the array");
		}
		
	}

}