The java final modifier can be attached to all classes, methods and variables, Each has a different meaning.

When attaching to a class [Prohibit inheritance]

If you add the final modifier to a class, that class cannot be inherited. An error will occur at the compilation stage.

//final modifier class
final class FinalDemo {
    String name = "Class with final";
    public final void getInfo() {
        System.out.println(this.name);
    }
}

//Small class
class FinalDemoChild extends FinalDemo {

}

class MyApp {
    public static void main(String[] args) {
        FinalDemoChild demo = new FinalDemoChild();
    }
}

Execution result

$ java Myapp
Error:(8, 21) java: final final_Cannot be inherited from demo

When attaching to a method [Prohibit override]

If you add final to a method of a class, you cannot override it in the method child class.

//Class with final
class FinalDemo {
    String name = "Class with final";
    public final void getInfo() {
        System.out.println(this.name);
    }
}

//Small class
class FinalDemoChild extends FinalDemo {
    @Override
    public void getInfo() {
        System.out.println(this.name + "Small class");
    }
}

class MyApp {
    public static void main(String[] args) {
        FinalDemoChild demo = new FinalDemoChild();
    }
}

Execution result

$ java MyApp
Error:(11, 17) java:FinalDemoChild getInfo()Is the Final Demo getInfo()Cannot be overridden
Overridden method is final

When attaching to a variable [Prohibition of reassignment (constant)]

If you add final to a variable (field), you cannot reassign it. That is a constant. Since it is not necessary to change it with instance, it seems that it is often declared with a class variable with static. Also, as in other languages, constants are written in all capital letters.

//Class with final
class FinalDemo {
    public static final String NAME = "Variable with final";
}


class MyApp {
    public static void main(String[] args) {
        //Change constant
        FinalDemo.NAME = "Reassignment";
    }
}

Execution result

$ java MyApp 
Error:(9, 18) java:You cannot assign a value to the final variable NAME