Java final keyword

Final is using for three purpose:

final is used to prevent method overriding
final is used to prevent inherit a class
final is used to make a variable constant

final is used to prevent overriding: A method declared as final can’t be overridden.

class A {

    final void show() {
    }
}

class B extends A {

    void show() { //error,   can’t 	override
    }
}

class A {

final void show() {

}

class B extends A {

void show() { //error, can’t override

}

Because show() declared as final, it can’t be overridden in B. If we attempt to do so, a compile time error will result.

2. final to prevent inheritance: Sometimes we wants to prevent a class from being inherited. To do this, the class declares as final. Declaring a class as final implicitly declares all its member as final.

final class A {
}

class B extends A { // error, can’t subclass A

}

final class A {

}

class B extends A { // error, can’t subclass A

}

3. final as constant: A variable can be declared as constant with the keyword final. It must be initialize while declaring. Once we declare a variable with keyword final it can’t be reinitialized in the program. It is similar to the const in c/c++.

final int x = 10;
x = 45;	//error

1 2	final int x = 10; x = 45; //error