import java.io.*;
1.用BufferedReader类和inputStreamReader类。
BufferedRead br = new BufferedRead(inputStreamReader(System.in));
String str= br.readLine();
2.用Scanner类
Scanner scan= new Scanner(System.in);
String str = scan.next();
int i=scan.nextInt();
float f=scan.nextFloat();
3.接收单个字符
char c = (char)System.in.read();