How many ways to prevent method overriding in Java?

JavaObject Oriented ProgrammingProgramming

Method overriding works because of the run-time method binding feature in Java. So, if we force the java compiler to do static binding for a method then we can prevent that method from being overridden in a derived class.

We can prevent method overriding in Java in 3 ways

  • By making method final in the base class
  • By making a method static in the base class
  • By making a method private in the base class

Final methods can not be overridden

By making a method final we are adding a restriction that derived class cannot override this particular method.

Example

Live Demo

class Base {
   public void show() {
      System.out.println("Base class show() method");
   }
   public final void test() {
      System.out.println("Base class test() method");
   }  
}
class Derived extends Base {
   public void show() {
      System.out.println("Derived class show() method");
   }
   // can not override test() method because its final in Base class
   /*
   *  public void test() { System.out.println("Derived class test() method"); }
   */
}
public class Test {
   public static void main(String[] args) {
      Base ref = new Derived();
   // Calling the final method test()
      ref.test();
   // Calling the overridden method show()
      ref.show();
   }
}

Output

Base class test() method
Derived class show() method

Static methods can not be overridden

We can not override the static methods in a derived class because static methods are linked with the class, not with the object. It means when we call a static method then JVM does not pass this reference to it as it does for all non-static methods. Therefore run-time binding cannot take place for static methods.

Example

Live Demo

class Base {
   public void show() {
      System.out.println("Base class show() method");
   }
   public static void test() {
      System.out.println("Base class test() method");
   }
}
class Derived extends Base {
   public void show() {
      System.out.println("Derived class show() method");
   }
      // This is not an overridden method, this will be considered as new method in Derived class
   public static void test() {
      System.out.println("Derived class test() method");
   }
}
public class Test {
   public static void main(String[] args) {
      Base ref = new Derived();
      // It will call the Base class's test() because it had static binding
      ref.test();
      // Calling the overridden method show()
      ref.show();
   }
}

Output

Base class test() method
Derived class show() method

Private methods can not be overridden

Private methods of the base class are not visible in a derived class, hence they cannot be overridden.

Example

Live Demo

class Base {
   public void show() {
      System.out.println("Base class show() method");
   }
   private void test() {
      System.out.println("Base class test() method");
   }
}
class Derived extends Base {
   public void show() {
      System.out.println("Derived class show() method");
   }
   // This is not an overridden method, this will be considered as other method.
   public void test() {
      System.out.println("Derived class test() method");
   }
}
public class Test {
   public static void main(String[] args) {
      Base ref = new Derived();
   // Cannot call the private method test(), this line will give compile time error
   // ref.test();
   // Calling the overridden method show()
      ref.show();
   }
}

Output

Derived class show() method
raja
Published on 12-Jun-2019 11:08:43
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