How do you upcast and downcast the same object in Java?

Converting one data type to others in Java is known as casting.

Up casting − If you convert a higher datatype to lower datatype, it is known as narrowing (assigning higher data type value to the lower data type variable).

Example

 Live Demo

import java.util.Scanner; public class NarrowingExample {    public static void main(String args[]){       char ch = (char) 67;       System.out.println("Character value of the given integer: "+ch);    } }

Output

Character value of the given integer: C

Down casting − If you convert a lower datatype to a higher data type, it is known as widening (assigning lower data type value to the higher data type variable).

Example

 Live Demo

public class WideningExample {    public static void main(String args[]){       char ch = 'C';       int i = ch;       System.out.println(i);    } }

Output

Integer value of the given character: 67

upcasting and downcasting the same object

Similarly, you can also cast/convert an object of one class type to others. But these two classes should be in an inheritance relation. Then,

• If you convert a Super class to subclass type it is known as narrowing in terms of references (Subclass reference variable holding an object of the superclass).

Sub sub = (Sub)new Super();

• If you convert a Subclass to Superclass type it is known as widening in terms of references (superclass reference variable holding an object of the subclass).

Super sup = new Sub();

Example

The following Java program demonstrates how to upcast and down cast the same object.

 Live Demo

class Person{    public String name;    public int age;    Person(){}    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 Student extends Person {    public String branch;    public int Student_id;    Student(){}    public Student(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 Person();       Student student = new Student("Krishna", 20, "IT", 1256);       //Up casting       person = student;       person.displayPerson(); //only super class methods       //Down casting       student = (Student) person;       student.displayPerson();       student.displayStudent();    } }

Output

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