DEV Community: Bala Murugan

Abstraction In Java

Bala Murugan — Fri, 12 Jun 2026 10:32:44 +0000

What is Abstraction:

Abstraction is an OOP concept that hides implementation details and shows only the essential features of an object.

Why Use Abstraction:

Reduces code complexity.
Improves security by hiding internal details.
Makes code easier to maintain and reuse.

When to Use Abstraction

Use abstraction when you want to define what an object should do without specifying how it does it. It is useful when multiple classes share common behavior but have different implementations.

Example:

Consider a car. A driver uses the steering wheel, brake, and accelerator without knowing how the engine works internally. The driver only sees the necessary features, while the internal implementation is hidden. This is abstraction.

code:

abstract class Animal {
    abstract void sound();   // Abstract method
}

class Dog extends Animal {
    void sound() {
        System.out.println("Dog barks");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal a = new Dog();
        a.sound();
    }
}

Output:

Dog barks

Explanation :

Animal is an abstract class.
sound() is an abstract method (no implementation).
Dog provides the implementation of sound().
We know that an animal makes a sound, but the exact sound depends on the animal.

This hides the implementation details and shows only the required behavior, which is called abstraction.

Sum of First n Numbers

Bala Murugan — Sun, 07 Jun 2026 14:06:14 +0000

Definition:

The sum of first n numbers means adding all numbers from 1 to n.

Example:

If n = 5

Sum = 1 + 2 + 3 + 4 + 5

Sum = 15

Algorithm:

1.Start

2.Read the number n

3.Initialize i = 1 and sum = 0

4.Check whether i <= n

5.Add i to sum

6.Increment i by 1

7.Repeat steps 4 to 6 until i > n

8.Print the sum

9.Stop

Flowchart:

N
|
Print Sum
|
Stop

code:

n = int(input("Enter a number: "))

i = 1
sum = 0

while i <= n:
    sum = sum + i
    i += 1

print("Sum =", sum)

Input:

Enter a number: 5

Sample Output:

Sum = 15

Factorial of a Given Number

Bala Murugan — Sun, 07 Jun 2026 13:57:07 +0000

Definition

The factorial of a number is the product of all positive integers from 1 to that number.

Formula

For a number n:

5! = 5 × 4 × 3 × 2 × 1 = 120
4! = 4 × 3 × 2 × 1 = 24.

Algorithm:

1.Start

2.Read the number n

3.Initialize fact = 1 and i = 1

4.Check whether i <= n

5.Multiply fact by i

6.Increment i by 1

7.Repeat steps 4 to 6 until i > n

8.Print the factorial value

9.Stop

Flowchart:

N
|
Print Factorial
|
Stop


code:

n = int(input("Enter a number: "))

fact = 1
i = 1

while i <= n:
    fact = fact * i
    i += 1

print("Factorial =", fact)

Input:

Enter a number: 5

Output:

Factorial = 120

Perfect Number

Bala Murugan — Sun, 07 Jun 2026 13:51:18 +0000

Definition :

A Perfect Number is a number that is equal to the sum of its proper divisors (excluding the number itself).

Example

Number = 6

Proper divisors of 6 are:

1
2
3

Sum = 1 + 2 + 3 = 6

Since the sum of the divisors is equal to the number, 6 is a Perfect Number.

Algorithm

1.Start

2.Read the number n

3.Initialize i = 1 and sum = 0

4.Check whether i < n

5.If n % i == 0, add i to sum.

6.Increment i by 1

7.Repeat steps 4 to 6 until i becomes equal to n

8.Check whether sum == n

9.If true, print Perfect Number

10.Otherwise, print Not a Perfect Number
Stop.

FLOWCHART:

    ┌───────┐
    │ Start │
    └───┬───┘
        │
        ▼
┌─────────────┐
│ Input n     │
└─────┬───────┘
      │
      ▼
┌─────────────┐
│ i = 1       │
│ sum = 0     │
└─────┬───────┘
      │
      ▼
  ┌────────┐
  │ i < n ?│
  └──┬──┬──┘
   Yes No
    │   │
    ▼   ▼

┌──────────┐
│sum == n ?│
└──┬────┬──┘
Yes No
│ │
▼ ▼
┌────────┐ ┌────────────┐
│ Print │ │ Print │
│Perfect │ │Not Perfect │
│Number │ │ Number │
└────┬───┘ └─────┬──────┘
│ │
▼ ▼
┌─────────┐
│ Stop │
└─────────┘

(If i < n)

▼

┌─────────┐
│n % i=0 ?│
└──┬───┬──┘
Yes No
│ │
▼ │
┌─────────┐
│sum=sum+i│
└────┬────┘
│
▼
┌─────────┐
│ i=i+1 │
└────┬────┘
│
└──────► Back to i < n ?

Code:

n = int(input("Enter a number: "))

i = 1
sum = 0

while i < n:
    if n % i == 0:
        sum += i
    i += 1

if sum == n:
    print("Perfect Number")
else:
    print("Not a Perfect Number")

Input 1
Enter a number: 6

Output 1
Perfect Number

Input 2

Enter a number: 10

Output 2
Not a Perfect Number

Prime Number

Bala Murugan — Sat, 06 Jun 2026 14:59:36 +0000

Definition:

A Prime Number is a number that has exactly two factors:

1
The number itself

Examples: 2, 3, 5, 7, 11, 13

Not Prime: 4, 6, 8, 9, 10 (because they have more than two factors).

Algorithm:

1.Start

2.Read the number n

3.Initialize i = 1 and count = 0

4.Check whether i <= n

5.If n % i == 0, increment count by 1

6.Increment i by 1

7.Repeat steps 4 to 6 until i > n

8.If count == 2, print "Prime Number"

9.Otherwise, print "Not a Prime Number"

10.Stop.

Flowchart:

  ┌───────┐
  │ Start │
  └───┬───┘
      │
      ▼

┌─────────────┐
│ Input n │
└─────┬───────┘
│
▼
┌─────────────┐
│ i = 1 │
│ count = 0 │
└─────┬───────┘
│
▼
┌───────┐
│i <= n?│
└──┬─┬──┘
Yes No
│ │
▼ ▼
┌─────────┐
│count=2 ?│
└──┬───┬──┘
Yes No
│ │
▼ ▼
┌────────┐ ┌────────────┐
│ Print │ │ Print │
│ Prime │ │ Not Prime │
└────┬───┘ └─────┬──────┘
│ │
▼ ▼
┌───────┐
│ Stop │
└───────┘

(If i <= n)

▼

┌─────────┐
│n % i=0 ?│
└──┬───┬──┘
Yes No
│ │
▼ │
┌───────────┐
│count+=1 │
└─────┬─────┘
│
▼
┌─────────┐
│ i=i+1 │
└────┬────┘
│
└──────► Back to i <= n

code:

n = int(input("Enter a number: "))

i = 1
count = 0

while i <= n:
    if n % i == 0:
        count += 1
    i += 1

if count == 2:
    print("Prime Number")
else:
    print("Not a Prime Number")

Output 1

Input:

Enter a number: 7

Output:

Prime Number

Output 2

Input:

Enter a number: 8

Output:

Not a Prime Number

Divisors of given number

Bala Murugan — Sat, 06 Jun 2026 14:50:17 +0000

Definition

A divisor (or factor) is a number that divides another number exactly without leaving any remainder.

For example, the divisors of 12 are:
1, 2, 3, 4, 6, 12

Because each of these numbers divides 12 completely.

Algorithm

Start

Read the number n

Set i = 1

Check whether i <= n

If true, check n % i == 0

If true, print i

Increment i by 1

Repeat steps 4 to 7 until i > n

Stop

Flowchart:

┌─────────┐
│ Start │
└────┬────┘
│
▼
┌──────────────┐
│ Input n │
└────┬─────────┘
│
▼
┌──────────────┐
│ i = 1 │
└────┬─────────┘
│
▼
┌──────────────┐
│ i <= n ? │◄─────────┐
└────┬─────┬───┘ │
│Yes │No │
▼ ▼ │
┌─────────┐ ┌─────────┐ │
│n%i==0 ? │ │ Stop │ │
└──┬───┬──┘ └─────────┘ │
│Yes│No │
▼ │ │
┌───────┐ │
│Print i│ │
└───┬───┘ │
│ │
▼ │
┌─────────┐ │
│ i=i+1 │────────────────┘
└─────────┘

Code:

n = int(input("Enter a number: "))
i = 1

while i <= n:
    if n % i == 0:
        print(i)
    i += 1

Example:

Input:

12

Output:

1
2
3
4
6
12

Problem: Multiples of 3 and 5

Bala Murugan — Sat, 06 Jun 2026 14:40:17 +0000

Definition

This program is used to print all numbers from 1 to n that are divisible by both 3 and 5. A number is considered a multiple of 3 and 5 if it is exactly divisible by both numbers without any remainder.

Algorithm

Step 1: Start

Step 2: Input n

Step 3: Initialize i = 1

Step 4: Check whether i <= n

Step 5: If i is divisible by both 3 and 5, print i

Step 6: Increment i by 1

Step 7: Repeat Steps 4 to 6 until i > n

Step 8: Stop.

Flowchart:

    ┌───────┐
    │ Start │
    └───┬───┘
        │
        ▼
  ┌──────────┐
  │ Input n  │
  └────┬─────┘
       │
       ▼
  ┌──────────┐
  │  i = 1   │
  └────┬─────┘
       │
       ▼
   ┌────────┐
   │ i <= n │
   └──┬───┬─┘
     Yes  No
      │    │
      ▼    ▼

┌────────────────┐
│ i%3==0 and │
│ i%5==0 ? │
└──┬─────────┬───┘
Yes No
│ │
▼ │
┌────────┐ │
│ Print i│ │
└────┬───┘ │
│ │
▼ │
┌────────┐ │
│ i=i+1 │◄────┘
└────┬───┘
│
└──────► Back to i <= n

        No
         │
         ▼
    ┌──────┐
    │ Stop │
    └──────┘

code:

n = int(input("Enter n: "))

i = 1

while i <= n:
    if i % 3 == 0 and i % 5 == 0:
        print(i)

    i = i + 1

Input:

Enter n: 30

Output:

15
30

Count of Divisors of Given Number

Bala Murugan — Sat, 06 Jun 2026 14:23:49 +0000

Definition

This program is used to find the total number of divisors (factors) of a given number.

A divisor is a number that divides another number exactly without leaving a remainder.

For example:

Divisors of 12 are: 1, 2, 3, 4, 6, 12
Total divisors = 6

The program uses a while loop to check all numbers from 1 to n and counts how many numbers divide n exactly.

Algorithm:

Step 1: Start
Step 2: Input n
Step 3: Set i = 1
Step 4: Set count = 0
Step 5: Check i <= n
Step 6: If n % i == 0, increment count by 1
Step 7: Increment i by 1
Step 8: Repeat Steps 5 to 7 until i > n
Step 9: Print count
Step 10: Stop.

Flowchart:

          ┌─────────┐
          │ START   │
          └────┬────┘
               │
               ▼
      ┌────────────────┐
      │   Input n      │
      └───────┬────────┘
              │
              ▼
     ┌─────────────────┐
     │ i = 1           │
     │ count = 0       │
     └───────┬─────────┘
             │
             ▼
         ┌───────┐
         │i <= n?│
         └──┬─┬──┘
          Yes No
           │   │
           │   ▼
           │ ┌──────────┐
           │ │Print Count│
           │ └────┬─────┘
           │      │
           │      ▼
           │   ┌─────┐
           │   │ END │
           │   └─────┘
           │
           ▼
      ┌───────────┐
      │n%i == 0 ? │
      └──┬────┬───┘
        Yes   No
         │     │
         ▼     │
  ┌──────────────┐
  │count=count+1 │
  └──────┬───────┘
         │
         ▼
    ┌─────────┐
    │ i=i+1   │
    └────┬────┘
         │
         └──────────► Back to i <= n

code:

n = int(input("Enter number: "))
i = 1
count = 0

while i <= n:
    if n % i == 0:
        count += 1
    i += 1

print("Count =", count)

Example:

Input:

Enter number: 12

Output:
Count = 6

Program: Multiples of 3 or 5

Bala Murugan — Sat, 06 Jun 2026 14:08:17 +0000

Definition

This program is used to print all numbers from 1 to n that are divisible by 3 or 5.

A number is printed if:

It is divisible by 3, or
It is divisible by 5, or
It is divisible by both 3 and 5.

The program uses a while loop to check each number from 1 to n.

Algorithm:

Step 1: Start
Step 2: Input n
Step 3: Initialize i = 1
Step 4: Check whether i <= n
Step 5: If i % 3 == 0 OR i % 5 == 0, print i
Step 6: Increment i by 1
Step 7: Repeat Steps 4 to 6 until i > n
Step 8: Stop.

Flowchart:

      ┌─────────┐
      │ START   │
      └────┬────┘
           │
           ▼
    ┌─────────────┐
    │  Input n    │
    └──────┬──────┘
           │
           ▼
    ┌─────────────┐
    │   i = 1     │
    └──────┬──────┘
           │
           ▼
       ┌────────┐
       │ i <= n │
       └──┬──┬──┘
        Yes No
         │   │
         │   ▼
         │ ┌─────┐
         │ │ END │
         │ └─────┘
         │
         ▼
 ┌─────────────────┐
 │ i%3==0 OR       │
 │ i%5==0 ?        │
 └──────┬────┬─────┘
      Yes    No
       │      │
       ▼      │
 ┌─────────┐  │
 │ Print i │  │
 └────┬────┘  │
      │       │
      └──┬────┘
         ▼
   ┌─────────┐
   │ i=i+1   │
   └────┬────┘
        │
        └────────► Back to i <= n

code:

n = int(input("Enter n: "))
i = 1

while i <= n:
    if i % 3 == 0 or i % 5 == 0:
        print(i)
    i += 1

Example:

Input:
n = 20

Output:

3
5
6
9
10
12
15
18
20

Multiples of 3 and 5

Bala Murugan — Sat, 06 Jun 2026 14:02:02 +0000

Definition:

This program is used to print all numbers between 1 and n that are divisible by both 3 and 5.

A number is a multiple of 3 and 5 if it leaves no remainder when divided by both numbers.

For example:

15 ÷ 3 = 5 and 15 ÷ 5 = 3
30 ÷ 3 = 10 and 30 ÷ 5 = 6

So, 15 and 30 are multiples of both 3 and 5.

Algorithm:

Step 1: Start
Step 2: Input n
Step 3: Set i = 1
Step 4: While i <= n
Step 5: If i % 3 == 0 and i % 5 == 0, print i
Step 6: Increment i by 1
Step 7: Repeat Steps 4 to 6
Step 8: Stop

Flow Chart:

      ┌─────────┐
      │  START  │
      └────┬────┘
           │
           ▼
    ┌─────────────┐
    │   Input n   │
    └──────┬──────┘
           │
           ▼
    ┌─────────────┐
    │    i = 1    │
    └──────┬──────┘
           │
           ▼
       ┌────────┐
       │ i <= n │
       └──┬──┬──┘
        Yes No
         │   │
         │   ▼
         │ ┌─────┐
         │ │ END │
         │ └─────┘
         │
         ▼
 ┌─────────────────┐
 │ i%3==0 and      │
 │ i%5==0 ?        │
 └──────┬────┬─────┘
      Yes    No
       │      │
       ▼      │
 ┌─────────┐  │
 │ Print i │  │
 └────┬────┘  │
      │       │
      └──┬────┘
         ▼
   ┌─────────┐
   │ i = i+1 │
   └────┬────┘
        │
        └──────────► Back to
                     i <= n

code:

n = int(input("Enter n: "))
i = 1

while i <= n:
    if i % 3 == 0 and i % 5 == 0:
        print(i)
    i += 1

OUTPUT:

15
30
45

Encapsulation in Java

Bala Murugan — Thu, 04 Jun 2026 06:33:47 +0000

What is Encapsulation:

Encapsulation is the process of binding data (variables) and methods into a single unit called a class. It is used to protect data from unauthorized access.

Encapsulation is achieved by:

Declaring variables as private.
Providing public getter and setter methods to access and update the data.

Why Use Encapsulation:

Provides data security.
Prevents unauthorized access.
Improves maintainability.
Provides better control over data.
Follows the principle of data hiding.

class Student {

    private String name;

    public void setName(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

public class Main {

    public static void main(String[] args) {

        Student s = new Student();

        s.setName("Bala");

        System.out.println(s.getName());
    }
}

Output:

Bala

Access Modifiers in Java

Access modifiers control the visibility and accessibility of classes, variables, methods, and constructors.

There are four types of access modifiers:

Public
Private
Protected
Default
Public

A public member can be accessed from anywhere in the program

public class Demo {

    public int age = 22;
}

Access:

Same class
Same package
Different package
Subclass

Private

A private member can be accessed only within the same class.

class Demo {

    private int age = 22;
}

Access:

Same class
Same package
Different package
Subclass

Protected

A protected member can be accessed within the same package and by subclasses.

class Demo {

    protected int age = 22;
}

Access:

Same class
Same package
Different package
Subclass

Default

When no access modifier is specified, it becomes default access.

class Demo {

    int age = 22;
}

Access:

Same class
Same package
Different package
Subclass (different package)

Constructors in Java

Bala Murugan — Wed, 03 Jun 2026 09:20:23 +0000

What is a Constructor?

A Constructor is a special method in Java that is automatically called when an object is created.

It is used to initialize object values.

Key Features of Constructor:

Constructor name must be the same as the class name.

Constructor does not have a return type (not even void).

Constructor is called automatically when an object is created.

Used to initialize object data.

Syntax:

class ClassName {

    ClassName() {
        // Constructor body
    }
}

Example:

public class Student {

    Student() {
        System.out.println("Constructor Called");
    }

    public static void main(String[] args) {

        Student s1 = new Student();
    }
}

Output:

Constructor Called

How it Works?

Student s1 = new Student();
↓
Constructor is called automatically
↓
Output: Constructor Called.

Why Do We Use Constructors?

To initialize object values.
To reduce repetitive code.
To set default values when an object is created.
To make object creation easier.

Types of Constructors:

Default Constructor:

class Student {

    Student() {
        System.out.println("Default Constructor");
    }
}

Parameterized Constructor:

class Student {

    String name;

    Student(String name) {
        this.name = name;
    }

    void display() {
        System.out.println(name);
    }

    public static void main(String[] args) {

        Student s1 = new Student("Bala");
        s1.display();
    }
}

Output:

Bala