Binary Search Feedback

Question

I have written a binary search algorithm, but it seems to be a bit different than other peoples that I've seen. I was hoping that the community could give me some feedback as to whether or not I'm missing something, or doing something the wrong way.

Binary Search:

import java.util.Arrays; 
public class BinarySearch {
 public int[] numbers = new int[] {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20}; 
 /**
 * @param num
 * @param key
 * 
 * Function recursively searches sorted array of integers, finding the specific number (key).
 * Search looks at the midpoint of array, checking to see if midpoint is number being sought,
 * if not, depending of whether the sought number is greater than, or less than, the midpoint
 * the function copies the upper, or lower, half of the array and passes it into a recursive 
 * function call.
 * 
 */
 public int performSearch(int[] num, int key){
 if(num.length == 0){
 System.out.println("Array empty"); 
 return 0; 
 }else{
 int mid; 
 int number=0; 
 mid = (num.length)/2; 
 if(key == num[mid]){
 number = num[mid]; 
 System.out.println("Found the number " + number); 
 return number; 
 }else if((key < num[mid]) && num.length > 1){
 num = Arrays.copyOfRange(num, 0, mid); 
 System.out.println("Low Range: " + Arrays.toString(num)); 
 return performSearch(num, key); 
 }else if((key > num[mid]) && num.length > 1){
 num = Arrays.copyOfRange(num, mid, num.length); 
 System.out.println("High Range: " + Arrays.toString(num)); 
 return performSearch(num, key); 
 }else{
 System.out.println("Number does not exist in array."); 
 return 0; 
 }
 //return number; 
 }
 }
 /**
 * @param args
 */
 public static void main(String[] args) {
 int key = 22; 
 BinarySearch bs = new BinarySearch(); 
 int index = bs.performSearch(bs.numbers, key); 
 System.out.println("Number " + index);
 }
}

• Farhan Ahmed: one problem I see with the code is that you are returning "num[mid]" where you should be returning "mid" in case the number is found!

Answer 1

I see 1 bug, 1 problem and 1 minor thing:

• as listed in the comment above: You are returning the number instead of the index. That's not very helpful for a binary search algorithm ;)
• when the array does not contain the item you are returning 0. 0 is a valid array index, by convention you'd return -1 in that case.
• not much of a problem but unnecessary: local variable number in first else block is obsolete.