java io流

import java.io.*;
public class Demo1
{
    public static void main(String args[])
    {
        try{
        InputStreamReader isr=new InputStreamReader(System.in);
        BufferedReader br=new BufferedReader(isr);
        System.out.println("请输入一个数");
        String str=br.readLine();
        System.out.println(str);
        }catch(Exception e)
        {
            e.printStackTrace();
        }
    }
}

        InputStreamReader isr=new InputStreamReader(System.in);
        BufferedReader br=new BufferedReader(isr);

BufferedReader br=new BufferedReader(new InputStreamReader(System.in));