What are the common mistakes in exception handling in Java?

Common mistakes in Java exception handling include: not catching exceptions, causing the application to terminate unexpectedly. Catching an exception without handling it leaves the error unresolved. The appropriate exception type was not used, obscuring the cause of the error. Exceptions are not logged, hampering troubleshooting. Use try-catch-finally when managing AutoCloseable resources instead of the simpler try-with-resources.

Common Mistakes in Java Exception Handling

In Java programming, exception handling is a crucial feature that allows The application handles errors gracefully and continues execution when exceptions occur. However, there are some common mistakes you may encounter when handling exceptions that can cause your code to execute erratically or be difficult to debug.

Not catching exceptions

The most common exception handling mistake is not catching the exception at all. This will cause an unhandled exception to terminate the application and print a stack trace in the console.

For example, the following code does not catch the NullPointerException exception:

public class Main {
    public static void main(String[] args) {
        String name = null;
        System.out.println(name.toUpperCase());  // 抛出 NullPointerException
    }
}

Does not handle the exception

After catching the exception, the important thing is Gotta deal with it. This means performing some action to resolve the error and allow the program to continue executing. There is no point in just catching an exception without handling it.

For example, the following code catches the NumberFormatException exception but does not handle it:

public class Main {
    public static void main(String[] args) {
        try {
            int number = Integer.parseInt("not a number");
        } catch (NumberFormatException e) {
            // TODO: 处理异常
        }
    }
}

Not using the appropriate exception type

It is important to use the exception type that best matches the specific exception condition. For example, use FileNotFoundException to indicate a file does not exist error instead of using IOException.

Do not log exceptions

Logging exceptions is an important step in troubleshooting and debugging. When an error occurs, logging exception details to a log file can help identify and resolve the problem. Exceptions can be logged to the console using the following code:

e.printStackTrace();

Use try-catch-finally instead of try-with-resources

For managing resources that implement the AutoCloseable interface (such as files and database connections), it is recommended to use the try-with-resources statement instead of the traditional try -catch-finally block. Use the try-with-resources statement to ensure that resources are properly closed at the end of the block.

Practical Case

Suppose we write an application to process user-entered scores. Here is sample code for handling fractional exceptions:

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        try {
            System.out.println("输入分数：");
            int score = scanner.nextInt();

            if (score < 0 || score > 100) {
                throw new IllegalArgumentException("分数必须在 0 到 100 之间。");
            }

            System.out.println("分数处理成功！");
        } catch (InputMismatchException e) {
            System.out.println("无效的分数输入。");
        } catch (IllegalArgumentException e) {
            System.out.println(e.getMessage());
        } finally {
            scanner.close();
        }
    }
}

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