Lecture 85:-  Exception Hierarchy in java

In Java, the exception hierarchy is organized as a class hierarchy, where different types of exceptions are represented by different classes. All exception classes in Java are derived from the Throwable class, which serves as the root of the exception hierarchy. The Throwable class has two main subclasses: Error and Exception.

1. Error:
   • Errors are exceptional conditions that generally cannot be handled by the application. They are typically caused by serious problems that are beyond the control of the programmer, such as system failures, out of memory errors, etc.
   • Examples of errors: OutOfMemoryError, StackOverflowError, NoSuchMethodError, AssertionError, etc.
2. Exception:
   • Exceptions represent exceptional conditions that can be handled and recovered from within the application. They occur during the normal execution of the program and may be caused by various factors, such as invalid inputs, I/O errors, arithmetic errors, etc.
   • Exceptions are further divided into two subtypes: checked exceptions and unchecked exceptions.
   • Checked Exceptions:
     • Checked exceptions must be either caught using a try-catch block or declared to be thrown in the method signature. These exceptions are known to be recoverable, and the compiler enforces their handling.
     • Examples of checked exceptions: IOException, SQLException, ParseException, InterruptedException, etc.
   • Unchecked Exceptions:
     • Unchecked exceptions, also known as runtime exceptions, do not need to be explicitly caught or declared. They usually indicate programming errors or logical issues within the application.
     • Examples of unchecked exceptions: NullPointerException, ArrayIndexOutOfBoundsException, ArithmeticException, IllegalArgumentException, etc.

Below is a simplified representation of the Java exception hierarchy:

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Throwable    ├── Error    │     ├── OutOfMemoryError    │     ├── StackOverflowError    │     ├── ...    │    └── Exception          ├── RuntimeException (Unchecked)          │     ├── NullPointerException          │     ├── IndexOutOfBoundsException          │     ├── ArithmeticException          │     ├── ...          │          └── IOException (Checked)                ├── FileNotFoundException                ├── SocketException                ├── ...

When writing Java code, you need to handle or declare checked exceptions explicitly, while unchecked exceptions usually indicate issues that need to be resolved in the code. By understanding the exception hierarchy, you can better manage exceptional situations and make your programs more robust and reliable.