Exception class hierarchy from Throwable

In Java, Throwable is the root class of everything that can be thrown. It has two direct subclasses: Error and Exception.

Throwable
 |
 +-- Error                      (unchecked)
 |    +-- VirtualMachineError
 |    |     +-- OutOfMemoryError
 |    |     +-- StackOverflowError
 |    +-- AssertionError
 |    +-- LinkageError
 |
 +-- Exception                  (checked)
      +-- IOException
      |     +-- FileNotFoundException
      |     +-- EOFException
      +-- SQLException
      +-- ReflectiveOperationException
      |     +-- ClassNotFoundException
      +-- InterruptedException
      +-- RuntimeException      (unchecked)
            +-- ArithmeticException
            +-- NullPointerException
            +-- ClassCastException
            +-- IndexOutOfBoundsException
            |     +-- ArrayIndexOutOfBoundsException
            +-- IllegalArgumentException
                  +-- NumberFormatException

Other subclasses of Exception include CloneNotSupportedException and TimeoutException.

Explanation

• Throwable: provides getMessage() and printStackTrace(); only its objects can be thrown or caught.
• Error: serious problems in the JVM or system that an application should not try to handle (OutOfMemoryError, StackOverflowError). Unchecked.
• Exception: conditions that a program can reasonably catch.
  • Checked exceptions (IOException, SQLException, ClassNotFoundException): the compiler requires try/catch or a throws clause.
  • Unchecked (runtime) exceptions (RuntimeException and its subclasses: ArithmeticException, NullPointerException, ArrayIndexOutOfBoundsException): caused by programming errors; handling them is optional.

Order of catch blocks: the specific subclass comes first, then its superclass.