final keyword in java

The final keyword in java is used to restrict the user. The java final keyword can be used in many context. Final can be:

1. variable
2. method
3. class

The final keyword can be applied with the variables, a final variable that have no value it is called blank final variable or uninitialized final variable. It can be initialized in the constructor only. The blank final variable can be static also which will be initialized in the static block only. We will have detailed learning of these. Let’s first learn the basics of final keyword.

1) Java final variable

If you make any variable as final, you cannot change the value of final variable(It will be constant).

Example of final variable

There is a final variable speedlimit, we are going to change the value of this variable, but It can’t be changed because final variable once assigned a value can never be changed.

class Bike9{  
 final int speedlimit=90;//final variable  
 void run(){  
  speedlimit=400;  
 }  
 public static void main(String args[]){  
 Bike9 obj=new  Bike9();  
 obj.run();  
 }  
}//end of class  

2. Java final Method

In Java, the final method cannot be overridden by the child class. For example,

class FinalDemo {
    // create a final method
    public final void display() {
      System.out.println("This is a final method.");
    }
}

class Main extends FinalDemo {
  // try to override final method
  public final void display() {
    System.out.println("The final method is overridden.");
  }

  public static void main(String[] args) {
    Main obj = new Main();
    obj.display();
  }
}

In the above example, we have created a final method named display() inside the FinalDemo class. Here, the Main class inherits the FinalDemo class.

We have tried to override the final method in the Main class. When we run the program, we will get a compilation error with the following message.

display() in Main cannot override display() in FinalDemo
  public final void display() {
                    ^
  overridden method is final

3. Java final Class

In Java, the final class cannot be inherited by another class. For example,

final class FinalClass {
    // create a final method
    public void display() {
      System.out.println("This is a final method.");
    }
}

class Main extends FinalClass {
  // try to override final method
  public  void display() {
    System.out.println("The final method is overridden.");
  }

  public static void main(String[] args) {
    Main obj = new Main();
    obj.display();
  }
}

In the above example, we have created a final class named FinalClass. Here, we have tried to inherit the final class by the Main class.

When we run the program, we will get a compilation error with the following message.

cannot inherit from final FinalClass
class Main extends FinalClass {