What is the exception hierarchy in Java?

Every exception in Java descends from Throwable, which splits into two branches, Error and Exception.

• Error covers serious problems such as OutOfMemoryError and StackOverflowError. A normal application should not try to catch these.
• Exception covers conditions an application may want to handle. Its subclass RuntimeException and everything below it are unchecked.

Every other subclass of Exception, such as IOException and SQLException, is checked. Error and its subclasses are unchecked too. The "Checked Exceptions" node in the tree is a grouping, not a real class. A catch (Exception e) block never catches an Error.

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