Exception hierarchy

Learn RuntimeException, IOException and others.

The exception hierarchy

All exceptions descend from Throwable. Error represents unrecoverable system failures; Exception can be handled by the programmer. The RuntimeException subclass is considered unchecked.

Throwable
  ├─ Error
  └─ Exception
       ├─ RuntimeException (unchecked)
       └─ IOException (checked)

Checked exceptions must be caught or declared with throws at compile time. IOException is an example. Unchecked ones are under RuntimeException; catching them is optional.

Common exception types

Some common exceptions: NullPointerException (using a null object), ArithmeticException (division by zero), ArrayIndexOutOfBoundsException (out of bounds index) and NumberFormatException (invalid number string).

Integer.parseInt("abc");
// NumberFormatException
int[] arr = new int[3];
int x = arr[5];
// ArrayIndexOutOfBoundsException

These all fall under RuntimeException; they are unchecked. Most can be prevented by careful coding; null checks, boundary checks and input validation are examples.

Exercise Catch an invalid number

Define String s = "abc";. Inside try call Integer.parseInt(s). Catch NumberFormatException and print Sayı değil.

Show example solution

try {
  int n = Integer.parseInt(s);
  System.out.println(n);
} catch (NumberFormatException e) {
  System.out.println("Sayı değil");
}

Test yourself

Which of the following is an unchecked exception?
- IOException
- Error
- RuntimeException
- Throwable
Show answer

RuntimeException — RuntimeException and its subclasses are unchecked; catching them is optional.
Match each exception to its category

IOException

Checked
RuntimeException

Unchecked
Error

System error
NullPointerException

null object error

Catch NumberFormatException

try {
  Integer.parseInt(s);
} catch (____ e) {
  System.out.println("Sayı değil");
}

Show answer

try {
  Integer.parseInt(s);
} catch (NumberFormatException e) {
  System.out.println("Sayı değil");
}

Next lesson: Multiple catch

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies