Explain the concept and hierarchy in the error handling system.

In Java, the error handling hierarchy is built on the Throwable class, which is divided into two main branches: Error and Exception.

• Error — serious errors that are usually not handled by the application (e.g., OutOfMemoryError).
• Exception — exceptions that can be handled.

Further, Exception is divided into:

• Checked exceptions — require mandatory handling or declaration in the method (e.g., IOException).
• Unchecked exceptions — descendants of RuntimeException, which do not require handling (e.g., NullPointerException).

The hierarchy allows structuring errors by type and importance, facilitating their handling and understanding of the code.