In Java, a final class is a class that cannot be extended by another class. A final class can be declared with the final keyword. Once a class is declared as final, it cannot be extended by any other class.

Here's an example of using a final class in Java:

final class MyClass {
    // class body
}

// this will generate a compile-time error, as the final class cannot be extended
class MySubclass extends MyClass {
    // subclass body
}

In the example above, MyClass is declared as a final class, which means it cannot be extended by another class. In the MySubclass class, attempting to extend the MyClass class will generate a compile-time error.

There are a few benefits of using final classes:

• final classes can prevent unintended changes to the behavior of a class by preventing it from being extended.
• final classes can improve code safety and stability by preventing unintended subclassing.
• final classes can improve code performance by allowing the compiler to make certain optimizations.

It's important to note that a final class can still have subclasses, but it cannot be extended by those subclasses. Additionally, a final class can still contain methods that are not final and can be overridden by subclasses. The final keyword only prevents the class itself from being extended.