Java Exception Handling

// Basic try-catch
try {
    int result = 10 / 0;  # may throw exception
} catch (ArithmeticException e) {
    System.out.println("Cannot divide by zero");
}

// Multiple catch blocks
try {
    int[] arr = new int[5];
    arr[10] = 50;  # out of bounds
} catch (ArrayIndexOutOfBoundsException e) {
    System.out.println("Index out of bounds");  # specific
} catch (Exception e) {
    System.out.println("General error");  # catch all
}

// Always executes
try {
    int result = 10 / 2;
} catch (Exception e) {
    System.out.println("Error");
} finally {
    System.out.println("Cleanup code");  # always runs
}

// Throw exception manually
public void checkAge(int age) {
    if (age < 18) {
        throw new ArithmeticException("Too young");  # force exception
    }
}

// Declare exception in method
public void readFile() throws IOException {  # method may throw
    FileReader file = new FileReader("file.txt");
    BufferedReader br = new BufferedReader(file);
    br.close();
}

// Create custom exception
public class InvalidAgeException extends Exception {
    public InvalidAgeException(String message) {
        super(message);  # pass to parent
    }
}

// Use custom exception
throw new InvalidAgeException("Age must be 18+");

// Auto-close resources
try (FileReader fr = new FileReader("file.txt")) {  # auto-close
    int c = fr.read();
} catch (IOException e) {
    e.printStackTrace();
}

// Checked exceptions (must handle)
IOException  # file operations
FileNotFoundException  # file not found
SQLException  # database errors

// Unchecked exceptions (runtime)
NullPointerException  # null reference
ArrayIndexOutOfBoundsException  # array index
ArithmeticException  # math errors
NumberFormatException  # invalid conversion