Java 如何在代码中添加或使用While循环

我想使用while循环，以便它可以捕获任何无效输入，如字母或随机%$@…等

我是java新手……非常感谢你们的帮助：） 以下是我的工作：

import java.util.Scanner; 

public class AreaCircle {

    public static void main(String[] args) {
Scanner sc = new Scanner(System.in); // read the keyboard
System.out.println("This program will calculate the area of a circle");

System.out.println("Enter radius:");//Print to screen

double r = sc.nextDouble(); // Read in the double from the keyboard


double area = (3.14 *r * r); 
String output = "Radius: " + r + "\n";
output = output + "Area: " + area + "\n";
System.out.println("The area of the circle  is " + area);

    }
}

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在下一个洞周围放一个试抓块。。。文档描述了扫描仪抛出的内容：

---

如果输入无效，

nextDouble

将抛出

InputMismatchException

。您可以将代码包围在do/while循环中，捕获异常并在收到有效输入时中断循环

boolean error = false;
do {
    try {
        System.out.println("Enter val: ");
        Scanner kbd = new Scanner(System.in);
        double r = kbd.nextDouble();
        error = false;
    } catch (InputMismatchException e) {
        error = true;
    }
}while(error);

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处理用户输入非常简单

我最近有一个程序检测到无效的用户输入

下面是我使用循环所做的：

static String[] letters = {"a","b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y"};

//declare an array of letters or number for your case
//and make a method to check if input key is present at the array..

 public int getIndexOf(char key){

        int charindex = -1;
        for(int index=0; index<letters.length; index++){            
            if(symbols[index] == key){
               charindex = index;
            }
        }

        return charindex;
    }

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就个人而言，我不会使用while循环，而是使用try/catch异常处理程序。你可以在它周围绕一圈，但我不知道你为什么要这么做。有一个名为NumberFormatException的内置异常，它是针对您所说的错误生成的。你所做的就是

try {
    double r = sc.nextDouble();
}
catch( NumberFormatException e ) {
    //put a message or anything you want to tell the user that their input was weird.
}

---

实际上，它所做的就是，如果输入的不是数字，那么进入catch块并打印消息。如果你愿意，为了有一个while循环，把所有的东西都放在while循环中。希望这能奏效

至少告诉我们你试过使用while循环。堆栈溢出不是一个代码工厂。你可能应该尝试用谷歌搜索它，看看这里：@user1190386:发生了什么错误？你包括导入语句了吗？好的，我这样做了…但是程序不会运行…在网络bean和终端上什么都没有出现？

boolean sentinel = false;
char[] numbervalue= input.getText().toString().toCharArray();

 for (int z = 0; z < numbervalue.length; z++) {
                    int m = bal.getIndexOf(plaintext[z]);
                  if(m == -1){
                   sentinel = false;
                  break;
}
                }

if(sentinel){
//prompt the user that the input contains invalid characters
}else{
//continue with the processing....
}

try {
    double r = sc.nextDouble();
}
catch( NumberFormatException e ) {
    //put a message or anything you want to tell the user that their input was weird.
}