Java Single Inheritance | extends Keyword

Single Inheritance

In single inheritance, one new class accesses the properties (fields and methods) of one old class.

Example

Consider an example of Bank. The bank contains all the basic details which are required to show to the users. When a new account is created then that account will automatically get the basic bank details from the bank instead of creating by user. Which saves the user time

See below program to understand Single Inheritance

Program Example

Develop a program for bank which contains two classes bank and user. The Bank is the Base class and User is the Derived class. Use the bank class data to display user details of bank using Single inheritance

import java.util.Scanner;
class Bank
{
    Scanner sc = new Scanner(System.in);
    String bank_name,branch,name;
    int acc_no,balance,contact_no;
	
    Bank()
    {
	bank_name = "National Bank";
	branch = "London";
    }
    void getDetails()
    {
	System.out.println("Enter name, account no and contact no : ");
	name = sc.next();
	acc_no = sc.nextInt();
	contact_no = sc.nextInt();
    }
    void displayDetails()
    {
	System.out.println("\nName : "+name);
	System.out.println("Account NO : "+acc_no);
	System.out.println("Contact NO : "+contact_no);
    }
}

class User extends Bank
{
    public static void main(String args[])
    {
	User u1,u2;
	u1 = new User();
	u2 = new User();
		
	u1.getDetails();
	u2.getDetails();
		
	System.out.println("Bank Name : "+u1.bank_name);
	System.out.println("Branch Name : "+u1.branch);
		
	u1.displayDetails();
	u2.displayDetails();
    }
}

Output

Example Explanation

• In above example we have taken Bank as Base class and User as Derived class. The extends keyword is used to access the properties of another class.
• The bank class contains the data which is reused by user class hence we have not created it again in the derived class.
• We have created two objects of a derived class because, In the inheritance base class object is never created. If we create base class object then there is no use of inheritance
• When the derived class object is created then the default constructor of base class is executed. Hence the values are initialized in the constructor
• We have called the getDetails() method by using u1 object because to store details in it. and again for u2 object.
• Next we have printed the bank name and branch using u1 object. we call use it by using any of these two objects, because these two details are copied into both of the objects.
• At last we have displayed the details of two objects

Constructor Execution

While in Inheritance, when we create an object of Derived class then Base class Default Constructor is executed first instead of Derived Class Default constructor. This is because of the highest priority of Base class constructor