如何添加或在我的代码中使用While循环

Question

我想使用while循环，因此它可以捕获任何无效的输入，如字母或随机%% $ @@等等

Im new to java ......对于很多球员乌尔THANKS帮助:) 这里是林工作：

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); 

    } 
} 

Answer 1

把周围nextDouble一个try-catch块...的文档描述了扫描器抛出什么：http://docs.oracle.com/javase/6/docs/api/java/util/Scanner.html#nextDouble%28%29

while(True) { 
    try { 
    do_parsing() 
    break; 
    } catch (EvilException e) { 
    continue; 
    } 
} 

Answer 2

如果t他输入无效，nextDouble会丢InputMismatchException。你可以将你的代码包含在一个do/while循环中，在那里你可以捕获异常并在接收到有效输入时打破循环。

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); 

Answer 3

这是非常简单的处理用户输入...

我最近有一个检测无效的用户输入的程序...

这里是我做过什么用循环：

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; 
    } 

那么您的输入： //所以你可以迭代虽然你输入

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; 
} 
       } 

然后你就可以做检查......

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

Answer 4

就个人而言，我不会用一个while循环，我会用一个try/catch异常处理程序。你可以在它周围放一段时间，但我不确定你为什么要这么做。有一个名为NumberFormatException的异常内置的异常，它用于像你所说的那样的错误。你要做的就是

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

从字面上看，所有它做的是，如果任何输入的不是一个数字，然后进入catch块，并打印您的消息。如果你愿意，为了有一个while循环，把所有的东西放在while循环中。希望这个作品！