Java Exception Handling FAQ & Assignment

An Exception is an event that disrupts the normal execution flow of a program. Exception handling allows developers to catch and handle such runtime events gracefully, maintaining application stability.

• Checked: Verified at compile-time (e.g. IOException).
• Unchecked: Detected at runtime (e.g. NullPointerException).

// Example
try {
  FileReader fr = new FileReader("file.txt");
} catch(IOException e) {
  System.out.println("Checked exception handled.");
}
      

1. try — Monitor risky code
2. catch — Handle the exception
3. finally — Execute cleanup code
4. throw — Manually raise exception
5. throws — Declare exception propagation

try {
   int num = 10 / 0;
} catch (ArithmeticException e) {
   System.out.println("Division by zero!");
} finally {
   System.out.println("Cleanup code runs here.");
}
      

• throw — Used to raise a specific exception instance.
• throws — Declares possible exceptions for a method.

void validate(int age) throws Exception {
  if(age < 18)
    throw new Exception("Underage");
}
      

No. A try must be followed by either catch or finally (or both).

• When System.exit() is invoked.
• When JVM crashes or power failure occurs.

Throwable
├── Error
│   ├── OutOfMemoryError
│   └── StackOverflowError
└── Exception
    ├── IOException (Checked)
    ├── SQLException (Checked)
    └── RuntimeException (Unchecked)
      ├── NullPointerException
      ├── ArithmeticException
      └── ArrayIndexOutOfBoundsException
      

class InvalidAgeException extends Exception {
  InvalidAgeException(String msg) {
    super(msg);
  }
}
      

When an exception is not handled in one method, it propagates to the calling method. This continues until caught or until the JVM terminates the program.