java获取当月天数，指定年月的天数，指定日期获取对应星期 .

 1 package com.example.administrator.dayofmonth;
 2 
 3 import java.text.SimpleDateFormat;
 4 import java.util.Calendar;
 5 import java.util.Date;
 6 
 7 /**
 8  * Created by 火龙裸先生 on 2017/4/11 0011.
 9  */
10 
11 public class Number_Of_Days {
12 
13     /**
14      * 获取当月的 天数
15      */
16     public static int getCurrentMonthDay() {
17 
18         Calendar a = Calendar.getInstance();
19         a.set(Calendar.DATE, 1);
20         a.roll(Calendar.DATE, -1);
21         int maxDate = a.get(Calendar.DATE);
22         return maxDate;
23     }
24 
25     /**
26      * 根据 年、月 获取对应的月份 的 天数
27      */
28     public static int getDaysByYearMonth(int year, int month) {
29 
30         Calendar a = Calendar.getInstance();
31         a.set(Calendar.YEAR, year);
32         a.set(Calendar.MONTH, month - 1);
33         a.set(Calendar.DATE, 1);
34         a.roll(Calendar.DATE, -1);
35         int maxDate = a.get(Calendar.DATE);
36         return maxDate;
37     }
38 
39     /**
40      * 根据日期 找到对应日期的 星期几
41      */
42     public static String getDayOfWeekByDate(String date) {
43         String dayOfweek = "-1";
44         try {
45             SimpleDateFormat myFormatter = new SimpleDateFormat("yyyy-MM-dd");
46             Date myDate = myFormatter.parse(date);
47             SimpleDateFormat formatter = new SimpleDateFormat("E");
48             String str = formatter.format(myDate);
49             dayOfweek = str;
50 
51         } catch (Exception e) {
52             System.out.println("错误!");
53         }
54         return dayOfweek;
55     }
56 
57 }