Question

求大大用java编写一个小程序

要求如下 当用户输入20以下的数字（int）的时候 用户可以继续输入 但是当输入20以上 或者其它字符的时候 显示error·

直接贴代码谢谢，

Answer 1

public class ReadDigits {

public static void main(String[] args) {

Scanner scanner = new Scanner(System.in);

System.out.println("Please input an integer(more than 20 or non-integer to end)");//提示输入

int inputValue = scanner.nextInt();

while(inputValue < 20){
System.out.println("Please input an integer(more than 20 or non-integer to end)");//小于20继续提示输入
try{
inputValue = scanner.nextInt();
}catch(InputMismatchException exp){
System.out.println("Error!Invalid value, program ends!");//类型出错，程序出错，停止哦
break;
}
if(inputValue >= 20 ){
System.out.println("Error! Invalid value, program ends!");//数字大于20，出错，程序停止额
break;
}
}
}
}

Answer 2

import java.util.InputMismatchException;
import java.util.Scanner;

public class ReadDigits {

public static void main(String[] args) {

Scanner scanner = new Scanner(System.in);

System.out.println("Please input an integer(more than 20 or non-integer to end)");//提示输入

int inputValue = scanner.nextInt();

while(inputValue < 20){
System.out.println("Please input an integer(more than 20 or non-integer to end)");//小于20继续提示输入
try{
inputValue = scanner.nextInt();
}catch(InputMismatchException exp){
System.out.println("Error!Invalid value, program ends!");//类型出错，程序出错，停止
break;
}

if(inputValue >= 20 ){
System.out.println("Error! Invalid value, program ends!");//数字大于20，出错，程序停止
break;
}
}

}
}

Answer 3

import java.util.InputMismatchException;
import java.util.Scanner;

public class ReadDigits {

public static void main(String[] args) {

Scanner scanner = new Scanner(System.in);

System.out.println("请输入数字：");//提示输入

int inputValue = scanner.nextInt();

while(inputValue < 20){
System.out.println("请继续输入数字：");//小于20继续提示输入
try{
inputValue = scanner.nextInt();
}catch(InputMismatchException exp){
System.out.println("Error!");//出错
break;
}

if(inputValue >= 20 ){
System.out.println("Error!");//数字大于20，出错，程序停止
break;
}
}

}
}

Answer 4

import java.io.*;
public class InputNum {
InputStreamReader ir;
BufferedReader br;
public static void main(String[] args) {
while(true){
try{
InputStreamReader ir=new InputStreamReader(System.in);
BufferedReader br=new BufferedReader(ir);
String line=br.readLine();
int aline=Integer.parseInt(line);
if(aline<=20){
System.out.println(line);
}
else{
System.out.println("请出入有效数字！");
break;
}
}
catch(Exception e){
System.out.println("请出入有效数字！");
break;
}
}

}

}
//如果什么地方不严密再和我说