Object Type Casting In Java

Object Casting

1. upcasting (casting is done implicitly)

2. downcasting (casting can be done explicit)

upcasting :- In java subclass object can be assign to super class object (parent class object), this casting is known as upcasting and it is done implicitly. (upwords in the hierarchy from subclass to super class).

Example:- 

Parent p = new Child();

OR

Parent p = new Parent();
Child c = new Child();
p  = c;   // Subclass to Super Class, it is valid 

using upcasting, we can access only parent class method and only ovverrided method in clild class.

Note: We can't access non-overrided method present in the child class means only methods present in the parent class can access by using upcasting.

downcasting :- Java does not permit to assign super class object to subclass object directly (means implicitly). So we need to do explicit casting to do downcasting.

Note: - "Before doing explicit casting, implicit casting must be done".

Example:-

Parent p = new Child(); // implicit casting
Child c = c = (Child) p;  // explicit casting

Parent Class (Super Class):

package com.javaiq.example.java;

public class Person {

	public void getPersonName() {
		System.out.println("getPersonName() :: In Parent Class :: I am a persion. ");
	}

	public void getParentName() {
		System.out.println("In Parent Class :: i am only in parent class not override in child class.");
	}

}

Child Class (Sub Class):

package com.javaiq.example.java;

public class Employee extends Person {

	@Override
        public void getPersonName() {
		System.out.println("getPersonName() :: In Employee Class :: I am a Employee.");
	}

	public void getEmployeeName() {
		System.out.println("In Employee Class :: I am a Employee - non override method .");
	}

}

Main Class:

package com.javaiq.example.java;

public class PersonMain {

	public static void main(String[] args) {

		System.out.println("#### Parent class Output ###");
		/*
		 * We can access all method present in Person class, here Person is Super Class
		 */
		Person person = new Person();
		person.getPersonName();
		person.getParentName();

		System.out.println("");
		System.out.println("#### Child Output ###");
		/*
		 * We can access all method present in Employee class and Person class, here
		 * Employee is Sub Class
		 */
		Employee employee = new Employee();
		employee.getPersonName();
		employee.getEmployeeName();
		employee.getParentName();

		System.out.println("");
		System.out.println("#### Upcasting Output ###");
		/*
		 * We can access only override in employee (Sub class) and all methods person (Super class)
		 * class methods
		 */
		Person personRef = new Employee();
		personRef.getPersonName();
		personRef.getPersonName();

		System.out.println("");
		System.out.println("#### Downcasting Output ###");
		Employee employeeRef1 = (Employee) personRef;
		employeeRef1.getPersonName(); // present in both class, and override in child class
		employeeRef1.getEmployeeName(); // only present in child class
		employeeRef1.getParentName(); // only present in parent class

	}

}

#### Parent class Output ###
getPersonName() :: In Parent Class :: I am a persion. 
In Parent Class :: i am only in parent class not override in child class.

#### Child Output ###
getPersonName() :: In Employee Class :: I am a Employee.
In Employee Class :: I am a Employee - non override method .
In Parent Class :: i am only in parent class not override in child class.

#### Upcasting Output ###
getPersonName() :: In Employee Class :: I am a Employee.
getPersonName() :: In Employee Class :: I am a Employee.

#### Downcasting Output ###
getPersonName() :: In Employee Class :: I am a Employee.
In Employee Class :: I am a Employee - non override method .
In Parent Class :: i am only in parent class not override in child class.

 

Related Tutorials:

• Data Types in Java
• Type Casting in Java
• Data Type Casting In Java
• Object Type Casting In Java