Java源码-第一个异常处理小程序：整数除法

Java how to program（中文名：Java大学教程）第10版第11章：深入理解异常（Exception Handling: A Deeper Look）中给出了一个整数除法的示例，用户输入除数和被除数时，任何一个出错，就必须重新来过。考虑到这样做不太人性化，决定改写一下。

代码如下：

package exercise;

//Fig. 11.3: DivideByZeroWithExceptionHandling.java
//Handling ArithmeticExceptions and InputMismatchExceptions.
import java.util.InputMismatchException;
import java.util.Scanner;

public class FirstExceptionHandler
{
//demonstrates throwing an exception when a divide-by-zero occurs
public static int quotient(int numerator, int denominator)
throws ArithmeticException
{
return numerator / denominator; // possible division by zero
}

public static void main(String[] args)
{
Scanner scanner = new Scanner(System.in);
boolean continueLoop = true; // determines if more input is needed
int numerator=0;
int denominator=0;
int result=0;

do
{
try // 读取被除数（整数）
{
System.out.print("请输入被除数： ");
numerator = scanner.nextInt();
continueLoop = false; // 正确读取到被除数，跳出while循环
}
//如果用户输入不是整数，则抛出inputMismatchException（输入不匹配异常）
catch (InputMismatchException inputMismatchException)
{
System.err.printf("%n发生异常：%s%n",
inputMismatchException);
System.out.printf(
"输入非法，请输入一个整数：%n%n");
scanner.nextLine(); // discard input so user can try again

}
} while (continueLoop);

continueLoop = true;//重置循环标记
do
{
try // 读取除数（非零整数）
{
System.out.print("请输入除数：");
denominator = scanner.nextInt();
result = quotient(numerator, denominator);
System.out.printf("%n计算结果： %d除以%d = %d%n", numerator,
denominator, result);
continueLoop = false; // input successful; end looping
}
catch (InputMismatchException inputMismatchException)
{
System.err.printf("%n发生异常：%s%n",
inputMismatchException);
scanner.nextLine(); // discard input so user can try again
System.out.printf(
"输入非法，请输入一个整数：%n%n");
}
catch (ArithmeticException arithmeticException)
{
System.err.printf("%n发生异常：%s%n", arithmeticException);
System.out.printf(
"整数除法中，除数不能为零，请重新输入！%n%n");
}
} while (continueLoop);
}
} // end class DivideByZeroWithExceptionHandling


运行结果：

请输入被除数： a

发生异常：java.util.InputMismatchException

输入非法，请输入一个整数：

请输入被除数： 11.1

发生异常：java.util.InputMismatchException

输入非法，请输入一个整数：

请输入被除数： 88

请输入除数：b

发生异常：java.util.InputMismatchException

输入非法，请输入一个整数：

请输入除数：0

发生异常：java.lang.ArithmeticException: / by zero

整数除法中，除数不能为零，请重新输入！

请输入除数：11

计算结果： 88除以11 = 8

参考：

原代码如下：

package example;

//Fig. 11.3: DivideByZeroWithExceptionHandling.java
//Handling ArithmeticExceptions and InputMismatchExceptions.
import java.util.InputMismatchException;
import java.util.Scanner;

public class DivideByZeroWithExceptionHandling
{
// demonstrates throwing an exception when a divide-by-zero occurs
public static int quotient(int numerator, int denominator)
throws ArithmeticException
{
return numerator / denominator; // possible division by zero
}

public static void main(String[] args)
{
Scanner scanner = new Scanner(System.in);
boolean continueLoop = true; // determines if more input is needed

do
{
try // read two numbers and calculate quotient
{
System.out.print("Please enter an integer numerator: ");
int numerator = scanner.nextInt();
System.out.print("Please enter an integer denominator: ");
int denominator = scanner.nextInt();

int result = quotient(numerator, denominator);
System.out.printf("%nResult: %d / %d = %d%n", numerator,
denominator, result);
continueLoop = false; // input successful; end looping
}
catch (InputMismatchException inputMismatchException)
{
System.err.printf("%nException: %s%n",
inputMismatchException);
scanner.nextLine(); // discard input so user can try again
System.out.printf(
"You must enter integers. Please try again.%n%n");
}
catch (ArithmeticException arithmeticException)
{
System.err.printf("%nException: %s%n", arithmeticException);
System.out.printf(
"Zero is an invalid denominator. Please try again.%n%n");
}
} while (continueLoop);
}
} // end class DivideByZeroWithExceptionHandling

备注：修改后虽然对用户更友好的同时，代码也变长了，突然理解了作者为什么没有写成我那样了。