Java学习记录(补充八:Date类;Java流(Stream),文件(File)和IO)

Posted 2020-10-04 天上一片红

Date类,Calendar类
package Box1;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Random;

//Date类
public class DateTest {
    public static void main(String[] args) {
        Date date = new Date();
        System.out.println(date);
        //System.out.println(date.getYear());
        
        //格式化时间
        SimpleDateFormat sf= new SimpleDateFormat("yyyy年MM-dd hh:mm:ss E");
        String dateString = sf.format(date);
        System.out.println(dateString);
        
        //练习:写一个方法，自动生成定单编号，规则：前2个字符为je 
        //后边14位为当前日期及时间，后面是四位随机数.
        //例如：je201708291456201890

        SimpleDateFormat change = new SimpleDateFormat("yyyyMMddhhmmss");
        String changeDate = change.format(date);
        Random a = new Random();
        int a1 = a.nextInt(10);
        int a2 = a.nextInt(10);
        int a3 = a.nextInt(10);
        int a4 = a.nextInt(10);
        System.out.println("je"+changeDate+a1+a2+a3+a4);
        
        
        //Calendar是抽象类,不能实例化,
        //能通过调用静态方法来实例化,用来产生对象的静态方法,一般称为工厂方法
        Calendar c= Calendar.getInstance();
        
        System.out.print(c.get(Calendar.YEAR)+"-");
        System.out.print(c.get(Calendar.MONTH)+1+"-");
        System.out.print(c.get(Calendar.DATE)+" ");
        System.out.print(c.get(Calendar.HOUR)+":");
        System.out.print(c.get(Calendar.MINUTE)+":");
        System.out.print(c.get(Calendar.SECOND)+" ");
        System.out.println(c.get(Calendar.DAY_OF_WEEK));//星期日是1
        
        //date与calendar互转
        Date d1 = c.getTime();
        System.out.println(sf.format(d1));
        
        c.setTime(date);
        
        //日期的计算
        Calendar c1 = Calendar.getInstance();
        //第一个参数:要加那个字段
        //第二个参数:要加多少
        c1.add(Calendar.DATE, 100);
        Date d2 = c1.getTime();
        System.out.println(sf.format(d2));
        
            
        //日期与字符串互转
        //Date转String用SimpleDateFormat
        Date d3 = new Date("2017/8/9");//格式不对会报错
        long d4= Date.parse("2017/10/10");
        Date d5 = new Date();
        d5.setTime(d4);
        
        //把字符串转成Date
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
        try {
            Date d6=format.parse("2017-08-09");
            System.out.println(d6);
        } catch (ParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        
        
        
        Calendar c2 = Calendar.getInstance();
        c2.set(2017, 9, 27, 20, 20,12);
        
        
    }
}

结果图:

 

枚举
package Box1;
//枚举:表示常量,提高代码的可读性
public enum Week {
    MON,TUE,WED,THU,SAT,SUN
}

package Box1;

public class WeekTestEnum {
    public static void main(String[] args) {
            System.out.println(Week.MON);
            Week n =Week.MON;
            switch (n) {
            case MON:
                System.out.println("周一");
                break;
            case TUE:
                System.out.println("周二");
                break;
            default:
                break;
            }
            
        }
}

结果图:

 

 

单例模式(重点)

 

 

 

 

Java流(Stream),文件(File)和IO

package com.jredu.iodemo;
//Java 流(Stream)、文件(File)和IO
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class IOTest {
    public static void main(String[] args) {
        try {
            FileInputStream fis=
                    new FileInputStream("G:/IO数据/io.text.txt");//调用文档
            //磁盘目录下的文档
            byte[]data = new byte[1024];
            int len;
            while((len=fis.read(data))!=-1){
                String s=new String(data,0,len);
                System.out.println(s);
            }
            fis.close();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        try {
            FileOutputStream fos = 
                    new FileOutputStream("G:/IO数据/io.text.txt");
            fos.write("abc".getBytes());//直接覆盖里面的内容
            fos.flush();
            fos.close();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        
        
        
    }
}

结果图::

package com.jredu.iodemo;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileCopyDemo {
    public static void main(String[] args) {
        try {
            FileInputStream fis = new FileInputStream("G:/IO数据/123.png");
            FileOutputStream fos = new FileOutputStream("G:/IO数据/1234.png");
            
            byte []data = new byte[1024];
            int len;
            try {
                while((len=fis.read(data))!=-1){
                    fos.write(data,0,len);
                }
                fis.close();
                fos.flush();
                fos.close();
                System.out.println(" copy OK!");
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
    }
}

结果图: