TimeDemo

package time;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
public class TimeDemo {

public static void main(String[] args) throws ParseException {
  timeTest();
  
  System.out.println("==============================");
  
  int year = 1987;
  int month = Calendar.JANUARY;
  int day = 20;
  int age = getAge(year, month, day);
  System.out.println("age=" + age);
  
  System.out.println("==============================");
  
  boolean isLeapYear = isLeapYear(2000);
  System.out.println(isLeapYear);
  
  System.out.println("==============================");
  
  
}
private static void timeTest() throws ParseException{
  /**
   * 由输出结果可知：
   *   java.util.Date         包含日期和时间
   *   java.sql.Date          只包含日期
   *      java.sql.Time      只包含时间
   *      java.sql.Timestamp 包含日期和时间
   *      java.util.Calendar 包含该类的所有字段的信息
   *  java.util.Date是java.sql.Date、java.sql.Time和java.sql.Timestamp的父类
   */
  java.util.Date uDate = new java.util.Date();
  java.sql.Date sDate = new java.sql.Date(uDate.getTime());
  java.sql.Timestamp ts = new java.sql.Timestamp(uDate.getTime());
  java.sql.Time time = new java.sql.Time(uDate.getTime());
  java.util.Calendar c = java.util.Calendar.getInstance();
  
  System.out.println("java.util.Date -> " + uDate + "\n"
       + "java.sql.Date -> " + sDate + "\n"
       + "java.sql.Timestamp -> " + ts + "\n"
       + "java.sql.Time -> " + time + "\n"
       + "java.util.Calendar -> " + c);
  
  System.out.println("==============================");
  
  System.out.println(System.currentTimeMillis() + "\n"
       + uDate.getTime() + "\n"
       + sDate.getTime()  + "\n"
       + ts.getTime()  + "\n"
       + time.getTime()  + "\n"
       + c.getTime());
  
  System.out.println("==============================");
  
  Date date = new Date();
  
  String format = new SimpleDateFormat("yyyy/MM/dd").format(date);
  System.out.println(format);
  
  date = new SimpleDateFormat("yyyy/MM/dd").parse(format);
  System.out.println(date);
  
  c.setTime(date);
  System.out.println(c.get(Calendar.DAY_OF_MONTH));
  
  System.out.println("==============================");
  
  //取当月的最后一天
  c = Calendar.getInstance();
  int maxDay = c.getActualMaximum(Calendar.DAY_OF_MONTH);
  format = new SimpleDateFormat("yyyy/MM/" + maxDay).format(c.getTime());
  System.out.println("当月的最后一天 -> " + format);
  
}

private static int getAge(int year, int month, int day){
  Calendar birthDate = new GregorianCalendar(year, month, day);
  Calendar today = Calendar.getInstance();
  int age = today.get(Calendar.YEAR) - birthDate.get(Calendar.YEAR);
  
  //若还没过生日，则age-1
  birthDate.add(Calendar.YEAR, age);
  if(today.before(birthDate)){
   age -= 1;
  }
  return age;
}

private static boolean isLeapYear(int year){
  GregorianCalendar cal = new GregorianCalendar();
  return cal.isLeapYear(year);
}

}