In this article we discuss about what is final keyword, why final keyword is used.
What is final in Java? | What is final class, method and variable?
In java final is like constant.
In java final keyword used with following ways:-
- final class
- final variable
- final methods
If final used in java following restriction happens:-
- If final use with class then that class can not inherited.
- If final use with variable then we can not change its value.
- If final use with method then we can not override.
In java, String is immutable means we can not change its value. You can see String class is final class.
Lets see all of them.
Final Class
When class declared with final keyword, it is called final class.
If class declared with final then that class does not inherited means another class can not extends final class.
If we extends final class then it programs give compile time error.
Example :- Final Class
final class FinalClass {
}
public class FinalDemo extends FinalClass{
public static void main(String[] args) {
System.out.println("Final class demo");
}
}
}
public class FinalDemo extends FinalClass{
public static void main(String[] args) {
System.out.println("Final class demo");
}
}
Output :-
Compile time error
Final Variable
When variable declared with final then it is called final variable.
Once we declare variable final then we can not change its value again. And if we try to assign another value then we get compile time error.
If we declare variable final then we have to compulsory assign value to variable otherwise it shows error.
But in constructor, static block it is not compulsory to assign value to final variable.
In java, Wrapper class are final. like Integer, Float, Double.
lets see example of final variable.
Example :- Final Variable
public class FinalDemo{
public static void main(String[] args) {
// final variable with assign value
final String finalVariable = "Programming Blog";
public static void main(String[] args) {
// final variable with assign value
final String finalVariable = "Programming Blog";
// Change the value of final variable.
finalVariable = "a";
System.out.println(finalVariable);
}
}
System.out.println(finalVariable);
}
}
Output :-
Compile time error
When to use final variable
The only difference between a normal variable and a final variable is
that we can re-assign value to a normal variable but we cannot change
the value of a final variable once assigned. Hence final variables must
be used only for the values that we want to remain constant throughout
the execution of program.
Final Method
When method declare with final it is called final method. Final method can not be overridden. means we can not override final methods.
Overriding means same method name and arguments but in different class.
Lets see example of override in java
Example :- Override in java
public class OverrideDemo {
public void methodOne() {
System.out.println("Method one in base class");
}
}
public void methodOne() {
System.out.println("Method one in base class");
}
}
public class Demo extends OverrideDemo {
public void methodOne() {
System.out.println("Method one in child class");
}
public static void main(String[] args) {
Demo obj = new Demo ();
obj.methodOne();
}
}
public void methodOne() {
System.out.println("Method one in child class");
}
public static void main(String[] args) {
Demo obj = new Demo ();
obj.methodOne();
}
}
Output :-
Method one in child class
Now lets see example of final method in java.
Example :- Final Method
public class FinalMethodDemo {
public final void finalMethod() {
System.out.println("Final method in base class");
}
}
public final void finalMethod() {
System.out.println("Final method in base class");
}
}
public class FinalDemo extends FinalMethodDemo{
public void finalMethod() {
System.out.println("Final method in child class");
}
public static void main(String[] args) {
FinalDemo obj = new FinalDemo();
obj.finalMethod();
}
}
public void finalMethod() {
System.out.println("Final method in child class");
}
public static void main(String[] args) {
FinalDemo obj = new FinalDemo();
obj.finalMethod();
}
}
Output :-
Compile time error
OTHER ARTICLES YOU MAY LIKE :-
- Double Brace Initialization in Java
- BiFunction in Java
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- Functional Interface in Java
- Abstraction in Java
- Static in Java (Static class, Method, Variable and Block)
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