响应用户输入 Scanner(System.in)

package c1;

import java.util.Scanner;

public class Test {

 /**
  * @param args
  */
 public static void main(String[] args) {

  Test t=new Test();
  t.selection();

 }
 public void selection(){
  System.out.println("please input [Y] or [N]");
  Scanner scanner = new Scanner(System.in);
  String str=scanner.nextLine();
  if(str.equalsIgnoreCase("Y")||str.equalsIgnoreCase("N")){
   System.out.println("your selection is correct;");
  }
  else{
   System.out.println("your selection is incorrect;");
   selection();

   //return; //you need add a return here if you have to add more codes in below
  }
  //System.out.println("here will be excuted twice or more times;");//这里不应该再有语句，否则在用户输入错误的情况下，可能会执行多次,除非在上面加了return语句。
 }
}