In what situations and for what purposes is the final modifier used in code?

The final modifier in Java is used to restrict modifications and enhance code safety:

• For variables: a variable declared as final can only be initialized once. This is useful for creating constants or preventing accidental changes to the value.

• For methods: a method declared as final cannot be overridden in subclasses. This ensures that the method's behavior remains unchanged.

• For classes: a class declared as final cannot be inherited. This is used when you want to prevent extension of the class, for example, to ensure security or integrity of logic.

Example:

public final class Constants {
    public static final double PI = 3.14159;
}

class Base {
    public final void show() {
        System.out.println("Final method");
    }
}

class Derived extends Base {
    // Error: cannot override final method
    // public void show() { }
}