1

我在java中的catch块有点困难。帮助将不胜感激。

do {
    System.out.println ("If you want to exit the program, press 0. To continue, press 1.");
        try {
            returnint = Input.nextInt();    
        } catch (Exception e) {
            returnint=12;
            return; //after this code executes, I CANNOT RE-ENTER A NUMBER
        } finally {
        if (!(returnint==1 || returnint==0)) {
            System.out.println ("Invalid response. Please retry.");
        } continue;
    } while (returnint!=1 && returnint!=0);

所以问题是由于某种原因，循环不会重复。对此有任何帮助，包括更好地理解 try-catch-finally 块，将不胜感激。

编辑：程序开始时还有一个 try 块，在程序返回那里后，它也会以某种方式触发它。这里有什么帮助吗？

编辑2：下面的完整代码。

import java.util.Scanner;


public class PrimeNumberChecker {

/**
 * @param args
 */
public static void main(String[] args) {
    int returnint=1;
    boolean isprime=true;
    Scanner Input = new Scanner(System.in); //creates scanner
do{ 
    long prime,root,primediv,i;
    try {
    System.out.println("Please input a number to be checked"); //prompts user for input
    prime = Input.nextLong();//detects and stores next int input
    }catch(Exception exc){
        System.out.println("The following exception has been thrown: "+exc+"  Program aborted.");
        returnint=0;
        return;
    }
    root=(long) Math.sqrt(prime); //takes the int sqrt of the input number
    for(i=2;(i<=root&&isprime==true);i++){ //for loop to check for prime factors
        if (prime%i==0) {  //if a number divides into the number exactly, this returns true
            isprime=false;  //and so this returns false
        }
    }

    if (isprime==false) {
        primediv=prime;
        System.out.println("The number is not prime.");
        System.out.println("The factors of the number are: ");
            for(i=2;primediv>1;i++) {   //this is a loop to factorise the number if it is NOT prime
                if (primediv%i==0) {   //if it finds a factor, it prints it and checks if the factor appears twice
                    primediv=primediv/i;
                    System.out.println(i);
                    i--;
                }
            }
    } else {
        System.out.print(prime);  //the output if the number is prime
        System.out.println(" is a prime number");
    }
    try {
        do {
            System.out.println ("If you want to exit the program, press 0. To continue, press 1.");
            if (!(returnint==1 || returnint==0)) {
                System.out.println ("Invalid response. Please retry.");
            }
            returnint = Input.nextInt();    
          continue;
        } while (returnint!=1 && returnint!=0);
    } catch (Exception e) {
        System.out.println("ERROR: " + e.getMessage());
        throw e;
    } finally {   
        System.out.println("Exit. Return value was set to " + returnint);
    }   
}while (returnint==1);
}

}

4

4 回答 4

0

这个怎么样：

int returnint = 0;
try {
    do {
        System.out.println ("If you want to exit the program, press 0. To continue, press 1.");
        if (!(returnint==1 || returnint==0)) {
            System.out.println ("Invalid response. Please retry.");
        }
        returnint = Input.nextInt();    
      continue;
    } while (returnint!=1 && returnint!=0);
} catch (Exception e) {
    System.out.println("ERROR: " + e.Message());
} finally {   
    System.out.println("Exit. Return value was set to " + returnint);
}
于 2013-09-23T15:01:51.703 回答
0

您想return摆脱困境catch。它应该是：

}catch(Exception e){
    returnint=12;
}finally{

使用该return语句，您的代码将返回到调用方法并跳过该方法的其余部分。根据块的操作方式，您的 finally 块仍将执行，try/catch/finally但您的其余代码都不会执行。

于 2013-09-23T14:29:38.157 回答
0

return 语句将控件返回给调用程序。您是否尝试过将其注释掉并查看执行情况。

首先确定捕获异常时要执行的操作的逻辑。

于 2013-09-23T14:27:44.643 回答
-1

为什么你在 catch 块中将 returnint 设置为 12。一旦你从一个方法返回，你就不能进入循环。Catch 块应该捕获异常并向用户显示有意义的消息或将异常抛出给调用类。在您的示例中，您已经吃掉了异常并像方法正常执行一样返回

于 2013-09-23T14:29:42.490 回答