Here you can find the source of days(int year, int month)
public static int days(int year, int month)
//package com.java2s; public class Main { public static int days(int year, int month) { int total = 30; switch (month) { case 1:// w w w .jav a 2 s. co m case 3: case 5: case 7: case 8: case 10: case 12: total = 31; break; case 2: if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) total = 29; else total = 28; break; default: break; } return total; } }