In Java, the final keyword is used as defining something as constant /final and represents the non-access modifier.

final variable

• When a variable is declared as final in Java, the value can’t be modified once it has been assigned.
• If any value has not been assigned to that variable, then it can be assigned only by the constructor of the class.

final method

• A method declared as final cannot be overridden by its children's classes.
• A constructor cannot be marked as final because whenever a class is inherited, the constructors are not inherited. Hence, marking it final doesn't make sense. Java throws compilation error saying - modifier final not allowed here

final class

• No classes can be inherited from the class declared as final. But that final class can extend other classes for its usage.