java8中新的Date和Time详解

新date类和time类背后的设计原则：

不可变类

java8之前，date类都是可变类。当我们在多线程环境下使用它，编程人员应该确认date对象的线程安全。java8的date和time api提供了线程安全的不可变类。编程人员不用考虑并发的问题。

领域模型驱动设计方法

新的日期和时间的类别遵循“域驱动设计”。对于开发者来说，理解方法和类的功能是很容易的。

接下来让我们来看看新date和time api:

1.java.time.localdate:

localdate只提供日期不提供时间信息。它是不可变类且线程安全的。

package org.smarttechie;
import java.time.localdate;
import java.time.temporal.chronounit;
/**
* this class demonstrates java 8 data and time api
* @author siva prasad rao janapati
* */
public class datetimedemonstration {
/**
* @param args
*/
public static void main(string[] args) {
  //create date localdate localdate = localdate.now();
  system.out.println("the local date is :: " + localdate); 
  //find the length of the month. that is, how many days are there for this month.
  system.out.println("the number of days available for this month:: " + localdate.lengthofmonth()); 
  //know the month name
  system.out.println("what is the month name? :: " + localdate.getmonth().name()); 
  //add 2 days to the today's date.
  system.out.println(localdate.plus(2, chronounit.days)); 
  //substract 2 days from today
  system.out.println(localdate.minus(2, chronounit.days)); 
  //convert the string to date
  system.out.println(localdate.parse("2017-04-07"));
 }
}

2.java.time.localtime:

localtime只提供时间而不提供日期信息，它是不可变类且线程安全的。

package org.smarttechie;
import java.time.localtime;
import java.time.temporal.chronounit;
/**
* this class demonstrates java 8 data and time api
* @author siva prasad rao janapati
* */
public class datetimedemonstration {
/**
* @param args
*/
public static void main(string[] args) {
  //get local time
  localtime localtime = localtime.now();
  system.out.println(localtime);
 //get the hour of the day
 system.out.println("the hour of the day:: " + localtime.gethour());
 //add 2 hours to the time.
 system.out.println(localtime.plus(2, chronounit.hours));
 //add 6 minutes to the time.
 system.out.println(localtime.plusminutes(6));
 //substract 2 hours from current time
 system.out.println(localtime.minus(2, chronounit.hours));
 }
}

3.java.time.localdatetime:

localdatetime提供时间和日期的信息，它是不可变类且线程安全的

package orr.smarttechie;
import java.time.localdatetime;
import java.time.temporal.chronounit;
/**
* this class demonstrates java 8 data and time api
* @author siva prasad rao janapati
*
*/
public class datetimedemonstration {
/**
* @param args
*/
public static void main(string[] args) {
  //get localdatetime object
  localdatetime localdatetime = localdatetime.now();
  system.out.println(localdatetime);
  //find the length of month. that is, how many days are there for this month.
  system.out.println("the number of days available for this month:: " + localdatetime.getmonth().length(true));
  //know the month name
  system.out.println("what is the month name? :: " + localdatetime.getmonth().name());
  //add 2 days to today's date.
  system.out.println(localdatetime.plus(2, chronounit.days));
  //substract 2 days from today
  system.out.println(localdatetime.minus(2, chronounit.days));
 }
}

4.java.time.year:

 year提供年的信息，它是不可变类且线程安全的。

package orr.smarttechie;
import java.time.year;
import java.time.temporal.chronounit;
/**
* this class demonstrates java 8 data and time api
* @author siva prasad rao janapati
*
*/
public class datetimedemonstration {
/**
* @param args
*/
public static void main(string[] args) {
  //get year
  year year = year.now();
  system.out.println("year ::" + year);
  //know the year is leap year or not
  system.out.println("is year[" +year+"] leap year?"+ year.isleap());
 }
}

 5.java.time.duration:

duration是用来计算两个给定的日期之间包含多少秒，多少毫秒，它是不可变类且线程安全的

6.java.time.period:

period是用来计算两个给定的日期之间包含多少天，多少月或者多少年，它是不可变类且线程安全的

package orr.smarttechie;
import java.time.localdate;
import java.time.period;
import java.time.temporal.chronounit;
/**
* this class demonstrates java 8 data and time api
* @author siva prasad rao janapati
*
*/
public class datetimedemonstration {
/**
* @param args
*/
public static void main(string[] args) {
  localdate localdate = localdate.now();
  period period = period.between(localdate, localdate.plus(2, chronounit.days));
  system.out.println(period.getdays());
 }
}