Exception Hierarchy

Throwable
│
├── Error
│   ├── OutOfMemoryError
│   ├── StackOverflowError
│   └── VirtualMachineError
│
└── Exception
    │
    ├── Checked Exceptions
    │   ├── IOException
    │   │   ├── FileNotFoundException
    │   │   └── EOFException
    │   ├── SQLException
    │   ├── ClassNotFoundException
    │   ├── InterruptedException
    │   └── ParseException
    │
    └── RuntimeException (Unchecked)
        ├── NullPointerException
        ├── ArithmeticException
        ├── ArrayIndexOutOfBoundsException
        ├── StringIndexOutOfBoundsException
        ├── ClassCastException
        ├── NumberFormatException
        ├── IllegalArgumentException
        ├── IllegalStateException
        └── ConcurrentModificationException

Level 1: Throwable

• Root of all errors and exceptions
• Only classes that can be thrown and caught

Level 2: Error , Exception

Error

Represents serious JVM-level problems.

Most used Errors

• OutOfMemoryError → Heap memory exhausted
• StackOverflowError → Deep / infinite recursion

Errors should not be handled, they should be fixed.

Exception

Represents problems an application can handle.

This splits into:

• Checked Exceptions
• Unchecked Exceptions (RuntimeException)

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Throwable is the root, Errors represent JVM failures, checked exceptions must be handled, and unchecked exceptions represent programming mistakes.

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Table of contents

• Custom Exceptions