Checked exceptions must be either caught or declared in the method signature, as they are checked at compile time and represent recoverable conditions like IOException. 2. Unchecked exceptions, which extend RuntimeException, are not checked at compile time and indicate programming bugs such as NullPointerException, and should be prevented through input validation and defensive coding rather than caught. 3. Handle checked exceptions only when meaningful recovery is possible; otherwise, propagate them using throws. 4. Avoid catching unchecked exceptions unless necessary for logging or graceful shutdown, and instead fix the underlying code to prevent them. 5. Use checked exceptions for expected, recoverable errors and unchecked exceptions for programming errors that should be corrected during development. 6. Do not overuse checked exceptions when the caller cannot reasonably recover, favoring unchecked exceptions in such cases. Proper exception handling improves code robustness and maintainability by ensuring errors are addressed appropriately.

In Java, exceptions are divided into two main categories: checked and unchecked exceptions. Understanding how to handle each properly is key to writing robust and maintainable code.

Know the Difference Between Checked and Unchecked Exceptions

• Checked exceptions are checked at compile time. These are typically situations that are expected to occur and can be recovered from, like IOException or SQLException. Java forces you to either catch them or declare them in the method signature using throws.

• Unchecked exceptions (also known as runtime exceptions) extend RuntimeException and are not checked at compile time. Examples include NullPointerException, ArrayIndexOutOfBoundsException, and IllegalArgumentException. These usually indicate programming bugs and are not required to be caught or declared.

  

Rule of thumb: Handle or declare checked exceptions. Fix the code to avoid unchecked exceptions.

How to Handle Checked Exceptions

For checked exceptions, you have two options:

1. Catch and handle them when recovery is possible.

   try (FileReader fr = new FileReader("file.txt")) {
       // do something
   } catch (FileNotFoundException e) {
       System.err.println("File not found: "   e.getMessage());
       // maybe log it, use a default file, etc.
   } catch (IOException e) {
       System.err.println("IO error: "   e.getMessage());
   }

2. Propagate them up using throws if the current method isn't the right place to handle them.

   public void readFile() throws IOException {
       FileReader fr = new FileReader("file.txt");
       // let caller handle the exception
   }

Prefer handling only when you can meaningfully recover. Otherwise, propagate.

How to Deal with Unchecked Exceptions

You generally should not catch unchecked exceptions unless you have a specific reason (like logging or graceful shutdown). Instead:

• Prevent them by validating inputs and using defensive programming.

  public void printLength(String str) {
      if (str == null) {
          throw new IllegalArgumentException("String cannot be null");
      }
      System.out.println(str.length());
  }

• Use assertions or validation libraries (like Apache Commons or Google Guava) to catch issues early.

• In rare cases, you might catch a runtime exception at a top level (e.g., in a web filter or main loop) to prevent crashes and log errors.

When to Use Each Type

• Use checked exceptions for recoverable conditions that the caller should anticipate and handle (e.g., file not found, network timeout).
• Use unchecked exceptions for programming errors (e.g., null reference, invalid argument) that should be fixed during development.

A common best practice: Don’t overuse checked exceptions. If the caller can’t reasonably recover, make it unchecked.

Basically, handle checked exceptions explicitly, avoid catching unchecked ones unless necessary, and write code to prevent them in the first place.

The above is the detailed content of How to handle checked vs unchecked exceptions in Java?. For more information, please follow other related articles on the PHP Chinese website!