Downcasting in Java

What is Downcasting?

Typecasting an object of the parent class to an object of the child class is called Downcasting in Java. We need to tell the Java compiler to perform the conversion explicitly by creating an object of the child type using a reference of the parent type. It is the opposite of upcasting, where a subclass reference is converted into a superclass reference automatically by the compiler.

Typecasting is a process in which one data type or object is converted into another. It works with primitive datatypes and reference types as well. In this article, we are going to learn about downcasting and its use with examples.

Syntax of Downcasting

The syntax to downcast an object is given below:

subClassName objectName = (subClassName) superclassReference;

Uses of Downcasting

You can use downcasting for the following purposes:

• Since Java does not allow direct access to attributes and methods of a subclass through a superclass reference, you can use downcasting to access them through object of superclass.
• When you are working with polymorphism and need to retrieve the original subclass type.
• When different object types share a common superclass type.

Example of Downcasting in Java

Let's see a practical implementation of Downcasting in Java.

class Library {
   void showResources() {
      System.out.println("Library provides various resources");
   }
}

class Student extends Library {
   void borrowBooks() {
      System.out.println("Student borrows books from the library");
   }
}

public class Example {
   public static void main(String[] args) {
      // Upcasting
      Library library = new Student();  
      // Type checking for Downcasting
      if (library instanceof Student) {  
         //  downcasting
         Student student = (Student) library;  
         student.borrowBooks();  
         student.showResources();
      } else {
         System.out.println("Error while Downcasting");
      }
   }
}

Output

The result of the above code is as follows:

Student borrows books from the library
Library provides various resources