java新手笔记25 日期格式化

1.系统时间

package com.yfs.javase;

import java.sql.Time;
import java.sql.Timestamp;
import java.util.Calendar;
import java.util.Date;

public class DateDemo1 {

	/**
	 * 时间表示法
	 */
	public static void main(String[] args) {
		// long表示法
		long now = System.currentTimeMillis();//获取系统时间毫秒值
		System.out.println("计算机时间: " + now);
		//date表示法
		Date date = new Date();
		System.out.println("util.Date : " + date);
		//子类
		java.sql.Date sDate = new java.sql.Date(now);
		System.out.println("sql.Date : " + sDate);
		Time time = new Time(now);
		System.out.println("time : " + time);
		Timestamp ts = new Timestamp(now);
		System.out.println("timestamp : " + ts);
		
		//calendar表示法
		Calendar cal = Calendar.getInstance();//获取实例
		System.out.println(cal.getClass().getName());
		System.out.println(cal);
		

	}

}

 2.Date类

package com.yfs.javase;

import java.sql.Time;
import java.sql.Timestamp;
import java.util.Calendar;
import java.util.Date;

public class DateDemo2 {

	/**
	 * date类
	 */
	public static void main(String[] args) {
		Date date = new Date();//系统时间
		System.out.println("util.Date : " + date);
//		Date d2 = new Date(2014,6,15);//已过时
//		System.out.println("d2 : " + d2);
		
		Date d3 = new Date(System.currentTimeMillis() - 1000 * 60 * 60);
		System.out.println("d3 : " + d3);
		
		System.out.println("d3.before(date) : " + d3.before(date));
		System.out.println("d3.after(date) : " + d3.after(date));
		System.out.println("d3.getTime() : " + d3.getTime());
		
	

	}

}

 3.calendar类

package com.yfs.javase;

import java.sql.Time;
import java.sql.Timestamp;
import java.util.Calendar;
import java.util.Date;

public class DateDemo3 {

	/**
	 * calendar类
	 */
	public static void main(String[] args) {
		Calendar cal = Calendar.getInstance();
		//获取信息
		int year = cal.get(Calendar.YEAR);
		int month = cal.get(Calendar.MONTH) + 1;// 0 - 11   1 -12
		int day = cal.get(Calendar.DATE);
		
		
		System.out.println("year = " + year);
		System.out.println("month = " + month);
		System.out.println("day = " + day);
		//System.out.println(Calendar.DATE);  星期日  1  - 7 
		System.out.println("星期 ： " + cal.get(Calendar.DAY_OF_WEEK));
		System.out.println("今年第几天 ： " + cal.get(Calendar.DAY_OF_YEAR));
		System.out.println("星期四 ： " + Calendar.THURSDAY);
		
		//设置
//		cal.set(Calendar.YEAR, 2013);
//		cal.set(Calendar.MONTH, 2);
//		cal.set(Calendar.DATE, 15);
//		
//		cal.set(2015, 0, 31, 8, 30, 25);
//		
//		System.out.println("cal = " +  String.format("%tF  %<tT", cal));
//		
		//计算
		cal.add(Calendar.DATE, -100);
		System.out.println("cal = " +  String.format("%tF", cal));
	

	}

}

 4.日期格式化

package com.yfs.javase;

import java.sql.Time;
import java.sql.Timestamp;
import java.util.Calendar;
import java.util.Date;

public class DateDemo4 {

	/**
	 * 格式化
	 */
	public static void main(String[] args) {
		Date date = new Date();
		System.out.println("date = " +  String.format("%tF  %tT", date,date));
		Calendar cal = Calendar.getInstance();
		System.out.println("cal = " +  String.format("%tF %<tT", cal));
		
		//字符串格式化
		System.out.printf("%d\n",123);//格式控制符
		System.out.printf("%c\n",97);//格式控制符
		//格式化方法
		String result = String.format("%c", 65);
		System.out.println("result = " + result );
	

	}

}

 5.格式化对象

package com.yfs.javase;

import java.sql.Time;
import java.sql.Timestamp;
import java.text.DateFormat;
import java.util.Calendar;
import java.util.Date;

public class DateDemo5 {

	/**
	 * 格式化
	 */
	public static void main(String[] args) {
		Date date = new Date();
		System.out.println("date = " + date);
		//格式化对象
		//DateFormat df = DateFormat.getDateInstance(DateFormat.FULL);
		DateFormat df = DateFormat.getDateInstance(DateFormat.LONG);
		//DateFormat df = DateFormat.getDateInstance(DateFormat.SHORT);
		System.out.println("实现类 ： " + df.getClass().getName());
		System.out.println(df.format(date));
		
		df = DateFormat.getTimeInstance(DateFormat.LONG);
		System.out.println(df.format(date));
		
		df = DateFormat.getDateTimeInstance(DateFormat.FULL, DateFormat.SHORT);
		System.out.println(df.format(date));
		
		
		

	}

}

 6.SimpleDateFormat

package com.yfs.javase;

import java.sql.Time;
import java.sql.Timestamp;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class DateDemo6 {

	/**
	 * 格式化
	 */
	public static void main(String[] args) {
		Date date = new Date();
		System.out.println("date = " + date);
		//格式化对象
		SimpleDateFormat  sdf = new SimpleDateFormat("yyyy@MM@dd  HH%mm%ss");
		System.out.println(sdf.format(date));
		sdf.applyPattern("dd日MM月yyyy年");
		System.out.println(sdf.format(date));
		
	}

}

 7.日期对象转化

package com.yfs.javase;

import java.sql.Time;
import java.sql.Timestamp;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class DateDemo7 {

	/**
	 * 对象转化
	 */
	public static void main(String[] args) {
		//long
		Date ud = new Date();
		//util.Date -> sql.Date
		java.sql.Date sd = new java.sql.Date(ud.getTime());
		//sql.Date -> util.Date 
		ud.setTime(sd.getTime());
		
		//util.Date -> Calendar
		Calendar cal = Calendar.getInstance();
		cal.setTime(ud);
		
		//Calendar -> util.Date 
		ud = cal.getTime();
		
		String s = "2008-08-08";
		//sd = s;
		sd = java.sql.Date.valueOf(s);
		System.out.println(sd);
		
		
	}

}