Describe the basic hierarchy of exceptions in Java. What are checked and unchecked exceptions?

In Java, the exception hierarchy starts with the Throwable class, which has two main subclasses:

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

In turn, Exception is divided into:

• Checked exceptions — exceptions that the compiler requires to be either handled (try-catch) or declared in the method signature (throws). Examples: IOException, SQLException.
• Unchecked exceptions — subclasses of RuntimeException that do not require mandatory handling. Examples: NullPointerException, IllegalArgumentException.

Checked exceptions are used for situations that can be foreseen and handled, such as input/output errors. Unchecked exceptions are for programming errors or unforeseen situations.

Example:

public void readFile(String path) throws IOException {
    // checked exception
}

public void processData(Object obj) {
    if (obj == null) {
        throw new NullPointerException(); // unchecked
    }
}