Mastering Java Abstract Classes and Interfaces

Posted on Apr 1, 2026 in State Administration

1. Abstract Classes in Java

abstract class Student {
    int rollNo;
    long regNo;

    void getInput(int r, long reg) {
        rollNo = r;
        regNo = reg;
    }

    abstract void course();
}

class Kiitian extends Student {
    void course() {
        System.out.println("Course - B.Tech. (Computer Science & Engg)");
    }

    void display() {
        System.out.println("Roll No - " + rollNo);
        System.out.println("Registration No - " + regNo);
        course();
    }
}

public class Main {
    public static void main(String[] args) {
        Kiitian k = new Kiitian();
        k.getInput(24158046, 1234567899L);
        k.display();
    }
}

2. Implementing Java Interfaces

interface Motor {
    int capacity = 5;

    void run();
    void consume();
}

class WashingMachine implements Motor {
    public void run() {
        System.out.println("Motor is running");
    }

    public void consume() {
        System.out.println("Motor is consuming power");
    }

    void showCapacity() {
        System.out.println("Capacity of the motor is " + capacity);
    }
}

public class Main {
    public static void main(String[] args) {
        WashingMachine wm = new WashingMachine();
        wm.showCapacity();
    }
}

3. Salary Calculation with Interfaces

import java.util.Scanner;

interface Salary {
    void earnings();
    void deductions();
    void bonus();
}

abstract class Manager implements Salary {
    double basic;

    Manager(double basic) {
        this.basic = basic;
    }

    public void earnings() {
        double da = 0.80 * basic;
        double hra = 0.15 * basic;
        double total = basic + da + hra;
        System.out.println("Earnings - " + (int) total);
    }

    public void deductions() {
        double pf = 0.12 * basic;
        System.out.println("Deduction - " + (int) pf);
    }
}

class Substaff extends Manager {
    Substaff(double basic) {
        super(basic);
    }

    public void bonus() {
        double bonus = 0.50 * basic;
        System.out.println("Bonus - " + (int) bonus);
    }
}

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double basic = sc.nextDouble();
        Substaff s = new Substaff(basic);
        s.earnings();
        s.deductions();
        s.bonus();
    }
}

4. Interface Inheritance Example

import java.util.Scanner;

interface Employee {
    void getDetails();
}

interface Manager extends Employee {
    void getDeptDetails();
}

class Head implements Manager {
    int empId;
    String empName;
    int deptId;
    String deptName;
    Scanner sc = new Scanner(System.in);

    public void getDetails() {
        System.out.print("Enter employee id - ");
        empId = sc.nextInt();
        sc.nextLine();
        System.out.print("Enter employee name - ");
        empName = sc.nextLine();
    }

    public void getDeptDetails() {
        System.out.print("Enter department id - ");
        deptId = sc.nextInt();
        sc.nextLine();
        System.out.print("Enter department name - ");
        deptName = sc.nextLine();
    }

    void display() {
        System.out.println("Employee id - " + empId);
        System.out.println("Employee name - " + empName);
        System.out.println("Department id - " + deptId);
        System.out.println("Department name - " + deptName);
    }
}

public class Main {
    public static void main(String[] args) {
        Head h = new Head();
        h.getDetails();
        h.getDeptDetails();
        h.display();
    }
}