Error Handling & Exceptions

Error Handling & Exceptions

Robust error handling is essential for reliable software. Proper exception handling prevents crashes, provides meaningful feedback, and helps developers diagnose problems.

Exception Types

  +---------------------------------------------------------+
  |              EXCEPTION HIERARCHY                         |
  +---------------------------------------------------------+
  |                                                         |
  |   Throwable                                             |
  |   ├── Error (unrecoverable: OutOfMemory, StackOverflow) |
  |   └── Exception                                         |
  |       ├── Checked Exceptions (must handle)              |
  |       │   ├── IOException                               |
  |       │   └── SQLException                              |
  |       └── RuntimeException (unchecked)                  |
  |           ├── NullPointerException                      |
  |           ├── ArrayIndexOutOfBoundsException            |
  |           └── IllegalArgumentException                   |
  |                                                         |
  +---------------------------------------------------------+

Try-Catch Best Practices

  // BAD: Swallowing exceptions
  try {
      readFile(path);
  } catch (Exception e) {
      // silently ignore
  }

  // GOOD: Handle and log appropriately
  try {
      readFile(path);
  } catch (FileNotFoundException e) {
      logger.warn("Config file not found, using defaults: " + path);
      return defaultConfig;
  } catch (IOException e) {
      logger.error("Failed to read config file", e);
      throw new ConfigException("Cannot load configuration", e);
  }

Custom Exceptions

  public class InsufficientFundsException extends Exception {
      private final double amount;
      private final double balance;

      public InsufficientFundsException(double amount, double balance) {
          super("Cannot withdraw $" + amount + " with balance $" + balance);
          this.amount = amount;
          this.balance = balance;
      }

      public double getAmount() { return amount; }
      public double getBalance() { return balance; }
  }

Error Handling Principles

• Don't catch exceptions you can't handle — let them propagate
• Use specific exception types rather than catching Exception
• Include meaningful error messages that help diagnose the problem
• Use try-with-resources to ensure cleanup happens
• Design your API to minimize the need for callers to catch exceptions

Key Takeaways

• Never silently swallow exceptions
• Create custom exceptions for domain-specific errors
• Distinguish between recoverable and unrecoverable errors
• Good error handling makes debugging much easier