图灵程序设计丛书——算法Alogrithms（第四版）书里面有关二分法查找的程序例子看不懂

import java.util.*;
public class BinarySearch {
   public static void main(String[] args) {
       //以下语句看不懂是什么作用？想请论坛的热心人帮忙解答。
       int[] whiteList = In.readInts(args[0]);
       Arrays.sort(whiteList);
       while(!StdIn.isEmpty()) {
           int key = StdIn.readInt();
           if(rank(key,whiteList) < 0) {
               StdOut.println(key);
           }                                                      

       }
   }
   public static int rank(int key, int[] a) {
       int lo =0;
       int hi = a.length -1;
       while(lo <= hi) {
           int mid = lo +(hi+lo)/2;
           if(key < a[mid]) {
               hi = mid -1;
           }else if(key > a[mid]) {
               lo = mid +1;
           }else {
               return mid;
           }
         

       }
       return -1;
   }
}