使用 Catch 处理异常的Java程序

例外是程序执行时发生的事件。由于此异常，程序的正常流程将受到干扰。每当方法中发生异常时，该方法都会创建一个对象并将该对象发送到运行时系统。比如需要打开的文件没有找到、类没有找到异常、算术异常、SQL异常等。

要处理这些异常，有 4 种标准技术：

• 试着抓
• 扔
• 投掷
• 使用 HandlerExceptionResolver 接口（仅在 Spring 框架中）

Catch 用法如下所述：

句法：

try {

    // Put the code in the try block which may occur any
    // kind of exception
}
catch (ExceptionName e) {

    
    // handle the exception
}

下面讨论两个例子：

1. 使用预定义的异常类
2. 使用定义自己的异常类

示例 1：使用带有预定义异常类的 catch

这是由 try 和 catch 块处理的预定义异常的示例。

Java

// Importing Classes/Files
import java.io.*;
import java.util.*;
  
// Importing Scanner Class for user input
import java.util.Scanner;
  
class GFG {
    
    // Main driver method
    public static void main(String[] args)
    {
        // Taking input from user
        Scanner input = new Scanner(System.in);
  
        // Taking input of first number
        System.out.println("Enter the first number");
        Integer number1 = input.nextInt();
  
        // Taking input of second number
        System.out.println("Enter the second number");
        Integer number2 = input.nextInt();
  
        // Considering values in order to show execution
        // number1 = 30; number2 = 10;
  
        try {
  
            // Dividing both the numbers
            int result = number1 / number2;
  
            // If number2 = 0, method will create the object
            // of ArithmeticException class and throw it
            System.out.println("Result is " + result);
            // Printing the result
        }
  
        // If there is any  exception in the try block
        // then catch will handle the exception
        catch (ArithmeticException e) {
  
            // Message printed after catching the exception
            System.out.println("Dividing by zero");
        }
    }
}

输出：

示例 2：通过定义异常类来使用 catch

在这个例子中，异常是用户定义的，其中异常类的写法如下：

Java

// Java Program to Use catch to handle the exception
  
// Importing generic Classes/Files
import java.io.*;
import java.util.*;
  
class GFG {
  
    // Main driver method
    public static void main(String[] args)
    {
  
        // Taking input from keyboard/user
        Scanner input = new Scanner(System.in);
  
        // Enter any name
        System.out.println("Enter the name");
        String name = input.next();
        try {
            // Enter age
            System.out.println("Enter the age");
  
            // Using nextInt function to read integer
            Integer age = input.nextInt();
            if (age <= 18) {
                MyException me = new MyException();
                throw me;
                // If age is less then equal to 18 then the
                // object of MyException class will be throw
                // here
            }
            else
  
            // If age is greater then 18 i.e no exception is
            // there then try block will execute
            {
                System.out.println("name:" + name);
                System.out.println("age:" + age);
            }
        }
        catch (MyException e)
        // If the exception will occur then the object that
        // throw in the try block will be copied in to this
        // object
        {
            System.out.println(e);
        }
    }
}
// User defined MyException class
class MyException extends RuntimeException {
    public String toString()
    {
        // toString method will get Override here
        return "Age must be greater then 18";
    }
}

Input 1:
Enter the name : Geek
Enter the age: 18

Output: 
Age must be greater then 18  // Age is equal to 18 so the exception is occured

Input 2:
Enter the name : Geek
Enter the age: 20

Output:
name: Geek
age:20                      // Age is greater then 18 so no exception.