JAVA 输入输出流

java笔记
Input/Output I/o

键盘 InPut---APP---OutPut

待补充图片

流 Stream :
字节 8bit
字符 16bit

字节流

1 InputStream 抽象

FileIutputStream

2 OutputStream 抽象

FileOutputStream

字符流

1 Reader

FileReader
InputStreamReder
BufferedReader

2 Writer

Filewriter
OutputStreamWriter
BufferedWriter

debug

鼠标双击命令的左边，可以从执行到那一行就结束
点击小虫子图标，进入debug界面
F3 F6都是快捷键 可以顺次一行一行往下运行，可以跳转到当前函数的定义处

字符：
readder:read(.)
writer:write(.)

字节：
InputStream:read()
OutputStream:write()

FileReader()
FileWriter()
只能读写一个或多个字符

InputStreamReader()
OutputStreamWriter()

BuferedReader(reader)
BufferedWriter(writer)
一次可以读写一个字符串对象

文件--对象--序列化（串行化）--文件

SQL入门

select * from ST;
select * from ST where age >10;
insert into ST
(no,name) values(2,"cde")
update--
delete---
create- - -
drop- - -

DataBase--DBMS --MySQL/SQLServer/Oracle

IO案例

import java.io.*;
public class KeyBoardOperation {//keyboard operation
    public static void main(String[] args) throws Exception {
        InputStreamReader isr=new InputStreamReader(System.in);
        BufferedReader br=new BufferedReader(isr);
        String s=br.readLine();
        double d=Double.parseDouble(s);
        int i=Integer.parseInt(s);
        System.out.println(d*2);
        System.out.println(i+3);
    }
}

import java.io.*;
public class FIleOperation {
    public static void main2(String[] args) {//一般的字节流
        try {
            FileInputStream fis=new FileInputStream("KeyBoardOperation.java");
            int d=fis.read();
            while(d>=0){
                System.out.print((char)d);
                d=fis.read();
            }
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    public static void main1(String[] args) {//字节流数组
        try {
            FileInputStream fis=new FileInputStream("KeyBoardOperation.java");
            byte dd[]=new byte[1024];
            int i=fis.read(dd);
            while(i>0){
                for(int j=0;j<i;j++)
                    System.out.print((char)dd[j]);
                i=fis.read(dd);
            }
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    public static void main3(String[] args) throws Exception {//用字符流
        FileInputStream fis=new FileInputStream("KeyBoardOperation.java");
        InputStreamReader isr=new InputStreamReader(fis);
        BufferedReader br=new BufferedReader(isr);
        String s=br.readLine();
        while(s!=null){
            System.out.println(s);
            s=br.readLine();
        }
    }
    public static void main4(String[] args) throws Exception{//输出字节流
        FileOutputStream fos=new FileOutputStream("Key.txt");
        for(int i=65,j=0;j<26;i++,j++)
            fos.write(i);
        fos.close();
    }
    public static void main5(String[] args) throws Exception {//用字符流BufferedReader复制文件
        BufferedReader br=new BufferedReader(
                new InputStreamReader(
                        new FileInputStream("KeyBoardOperation.java")
                        )
                );
        BufferedWriter bw=new BufferedWriter(
                new OutputStreamWriter(
                        new FileOutputStream("KeyBoardOperation.txt")
                        )
                );
        String s=br.readLine();
        while(s!=null){
            bw.write(s);
            bw.newLine();
            s=br.readLine();
        }
        bw.close();
    }
    public static void main(String[] args) throws Exception {//用字符流FileReader复制文件
        BufferedReader br=new BufferedReader(
                new FileReader("KeyBoardOperation.java")
                );
        BufferedWriter bw=new BufferedWriter(
                new FileWriter("KeyBoardOperation.txt")
                );
        String s=br.readLine();
        while(s!=null){
            bw.write(s);
            bw.newLine();
            s=br.readLine();
        }
        bw.close();
    }
}

注：文件读取/导出 只能在和当前包在一个文件夹里面