二分法

while 起始位置  <= 终止位置

起始位置 

终止位置

查询位置等于（起始+终止）/2

目标值大于查询目录则  起始位置=查询位置等于 +1  即删除左侧，以右侧为全局并重新进行

public class Test20180506{

public static void main(String args[]){
Date[] days = new Date[5];
days[0] = new Date (2009,05,01);
days[1] = new Date (2010,05,01);
days[2] = new Date (2011,05,01);
days[3] = new Date (2012,05,01);
days[4] = new Date (2013,05,01);
Date d  = new Date (2011,05,01);

System.out.println(binarySearch(days,d));


}


public static int binarySearch(Date[] days, Date d){
if (days.length == 0) return -1;
int starPos = 0;
int endPos = days.length-1;
int m = (starPos+endPos)/2;

while (starPos <= endPos){
if (d.compare(days[m])== 0)  return m; 
}
if (d.compare(days[m]) > 1) {
starPos = m + 1;
}
if (d.compare(days[m]) < 1){
endPos = m -1 ;
}
return -1;
}
}


class Date{
int year;
int month;
int day;


Date (int y, int m, int d){
year = y;
month = m;
day = d;
}


public int compare(Date date){
return  year > date.year ? 1
  :year < date.year ? -1
  :month > date.month ? 1
  :month < date.month ? -1
  :day > date.day ? 1 
  :day < date.day ? -1
  :0;
}
}