class Animal {
  public void show() { // same method name
    System.out.println("I am an animal.");
  }
}

class Cat extends Animal {
  @Override // overrides the parent class -> annotation 
  public void show() { // same method name
    System.out.println("I am a cat.");
  }
}

class Main {
  public static void main(String[] args) {
    Cat c1 = new Cat();
    c1.show();
  }
}

Output: I am a cat

The above Program has show() in both parent (Animal()) and subclass (Cat()) in which the subclass overrides the parent class method.

Note: We have used annotation in our example. We may or may not use this annotation, however, we are using it to satisfy all the rules related to method overriding.

Rules for Method Overriding:

• Both parent and child classes have the same method name.
• There must be an IS-A relationship (inheritance).
• Private methods can not be overridden.

Example:

Code:

//Base class or Superclass
class Parent {
  //Access modifier of parent method is private
  // This method can not override the child class method
  private void display() {
    System.out.println("parent method is executed");
  }
}

//Derived class or Subclass
class Child extends Parent {

  //Below method can not overrides the Parent display() method 
  //This method is unique to the child class
  private void display() {
    System.out.println("child method is executed");
  }
}
//Driver class 
public class MethodOverriding3 {
  public static void main(String args[]) {
    Parent parentObject = new Parent();
    parentObject.display(); // this line when execute will throw compiler error

    Parent childObject = new Child();
    childObject.display(); // this line when execute will throw compiler error
  }
}

Output :

parent method is executed

child method is executed

// Simple Java program showing 
// final methods cannot be overridden 
//Parent class or Superclass  
class Parent {
  // Can't be overridden 
  final void display() {}
}
//Child class or Subclass  
class Child extends Parent {
  // This would produce compile time error 
  void display() {}
}

Output:

//Base class or SuperClass
class Parent {

  static void display() {
    System.out.println("parent static method is executed");
  }

  void show() {
    System.out.println("parent non-static (instance) method is executed");
  }
}

//Derived class or SubClass
class Child extends Parent {

  //This method hides the Parent display() method 
  static void display() {
    System.out.println("child static method is executed");
  }
  // This method overrides the Parent show() method
  void show() {
    System.out.println("child non-static (instance) method is executed");
  }
}

//Driver Class
public class MethodOverriding4 {
  public static void main(String args[]) {
    Parent childObject = new Child();
    // static method can not be overridden,
    // so below line calls parent display() method
    childObject.display();
    // Expected child method will run
    childObject.show();
  }
}