JAVA基础（标准输入流）

1，什么是标准输入输出流(

• System.in是InputStream, 标准输入流, 默认可以从键盘输入读取字节数据

• System.out是PrintStream, 标准输出流, 默认可以向Console中输出字符和字节数据

 

2，修改标准输入输出流

• 修改输入流: System.setIn(InputStream)

• 修改输出流: System.setOut(PrintStream)

【1】 SystemInOut

public class Demo06_SystemInOut {

    public static void main(String[] args) throws IOException {

        //demo1();

        System.setIn(new FileInputStream("a.txt"));            //改变标准输入流

        System.setOut(new PrintStream("b.txt"));            //改变标注输出流

        

        InputStream is = System.in;                            //获取标准的键盘输入流,默认指向键盘,改变后指向文件

        PrintStream ps = System.out;                        //获取标准输出流,默认指向的是控制台,改变后就指向文件

        

        int b;

        while((b = is.read()) != -1) {

            ps.write(b);

        }

        //System.out.println();                                //也是一个输出流,不用关,因为没有和硬盘上的文件产生关联的管道

        is.close();

        ps.close();

        

    }



    public static void demo1() throws IOException {

        InputStream is = System.in;

        int x = is.read();

        System.out.println(x);

        

        is.close();

        

        InputStream is2 = System.in;

        int y = is2.read();

        System.out.println(y);

    }





}

 

3，修改标准输入输出流拷贝图片

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.IOException;

import java.io.InputStream;

import java.io.PrintStream;

public class Test2 {

    public static void main(String[] args) throws IOException {

        System.setIn(new FileInputStream("元.jpg"));            //改变标准输入流

        System.setOut(new PrintStream("copy.jpg"));             //改变标准输出流

        

        InputStream is = System.in;

        PrintStream ps = System.out;

        

        byte[] arr = new byte[1024];

        int len;

        

        while((len = is.read(arr)) != -1) {

            ps.write(arr, 0, len);

        }

        is.close();

        ps.close();

    }

}