What is the purpose and use of the final keyword in programming?

In Java, the final keyword is used to restrict modifications and ensure immutability in different contexts:

• For variables: a variable declared as final cannot be reassigned after initialization. This guarantees that the value remains constant.

• For methods: a method declared as final cannot be overridden in subclasses, which helps protect the method implementation from changes.

• For classes: a class declared as final cannot be subclassed, meaning you cannot create a subclass of such a class.

Example of usage:

final int MAX_COUNT = 10;

final class Utility {
    public final void doSomething() {
        // implementation
    }
}

// Attempting to extend Utility will cause a compile-time error
// class ExtendedUtility extends Utility {} // Error