How to convert a super class variable into a sub class type in Java

Inheritance is a relation between two classes where one class inherits the properties of the other class. This relation can be defined using the extends keyword as −

public class A extends B{
}

The class which inherits the properties is known as sub class or, child class and the class whose properties are inherited is super class or, parent class.

In inheritance a copy of super class members is created in the sub class object. Therefore, using the sub class object you can access the members of the both classes.

Converting a super class reference variable into a sub class type

You can try to convert the super class variable to the sub class type by simply using the cast operator. But, first of all you need to create the super class reference using the sub class object and then, convert this (super) reference type to sub class type using the cast operator.

Example

Live Demo

class Person{
   public String name;
   public int age;
   public Person(String name, int age){
      this.name = name;
      this.age = age;
   }
   public void displayPerson() {
      System.out.println("Data of the Person class: ");
      System.out.println("Name: "+this.name);
      System.out.println("Age: "+this.age);
   }
}
public class Sample extends Person {
   public String branch;
   public int Student_id;

   public Sample(String name, int age, String branch, int Student_id){
   super(name, age);
      this.branch = branch;
      this.Student_id = Student_id;
   }
   public void displayStudent() {
      System.out.println("Data of the Student class: ");
      System.out.println("Name: "+super.name);
      System.out.println("Age: "+super.age);
      System.out.println("Branch: "+this.branch);
      System.out.println("Student ID: "+this.Student_id);
   }
   public static void main(String[] args) {        
      Person person = new Sample("Krishna", 20, "IT", 1256);      
      //Converting super class variable to sub class type
      Sample obj = (Sample) person;      
      obj.displayPerson();
      obj.displayStudent();
   }
}

Output

Data of the Person class:
Name: Krishna
Age: 20
Data of the Student class:
Name: Krishna
Age: 20
Branch: IT
Student ID: 1256

Example

Live Demo

class Super{
   public Super(){
      System.out.println("Constructor of the super class");
   }
   public void superMethod() {
      System.out.println("Method of the super class ");
   }
}
public class Test extends Super {
   public Test(){
      System.out.println("Constructor of the sub class");
   }
   public void subMethod() {
      System.out.println("Method of the sub class ");
   }
   public static void main(String[] args) {        
      Super sup = new Test();      
      //Converting super class variable to sub class type
      Test obj = (Test) sup;      
      obj.superMethod();
      obj.subMethod();
   }
}

Output

Constructor of the super class
Constructor of the sub class
Method of the super class
Method of the sub class

Krishna Kasyap

Published on 08-Feb-2021 16:05:52