Forem: S Sarumathi

String In Java

S Sarumathi — Tue, 19 May 2026 16:05:13 +0000

In Java, a String is an object used to store a sequence of characters.
A String in Java is a predefined class used to store text data or a collection of characters.
Java treats every text value inside double quotes (" ") as a String.
Java Strings are immutable, which improves security and performance
Without String, handling text data in programs becomes difficult.

Why String is Used:

String is mainly used to store:

Names
Messages
Email IDs
Addresses
Passwords
Sentences

Two way of creating String:

1. Using String Literal:

String name = "Java";

Explanation:

String → datatype/class
name → variable name
"Java" → string value

This is the most commonly used method.

Java stores this inside the String Constant Pool.

2. Using new Keyword:

String name = new String("Java");

Explanation:

Creates a new String object in heap memory
Even if "Java" already exists, a new object is created

Program:

public class Main {

    public static void main(String[] args) {

        String s1 = "Hello";

        String s2 = new String("World");

        System.out.println(s1);
        System.out.println(s2);
    }
}

Output:

Abstraction

S Sarumathi — Sat, 16 May 2026 19:50:48 +0000

Abstraction is one of the core concepts of Object-Oriented Programming (OOP) in Java.

Abstraction means hiding the internal implementation details and showing only the essential functionality to the user.

Why Abstraction is Important:

Abstraction helps developers to:

Hide complex implementation
Improve security
Reduce code complexity
Increase code reusability
Make applications easier to maintain

Program:

abstract class Animal {

    // abstract method
    abstract void sound();

    // normal method
    void sleep() {
        System.out.println("Animal is sleeping");
    }
}

class Dog extends Animal {

    // implementation of abstract method
    void sound() {
        System.out.println("Dog barks");
    }
}

public class Main {

    public static void main(String[] args) {

        Dog d1 = new Dog();

        d1.sound();
        d1.sleep();
    }
}

Output:

Encapsulation

S Sarumathi — Sat, 16 May 2026 19:48:23 +0000

Encapsulation is one of the important concepts of Object-Oriented Programming (OOP).
It is the process of wrapping data (variables) and methods into a single unit called a class.
In encapsulation, class variables are usually declared as private and accessed using public getter and setter methods.

Why Encapsulation is Used:

Encapsulation helps to:

Protect data from unauthorized access
Improve security
Control data modification
Make code clean and maintainable

Program:

class Student {

    // private variables
    private int id;
    private String name;

    // setter methods
    public void setId(int id) {
        this.id = id;
    }

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

    // getter methods
    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }
}

public class Main {

    public static void main(String[] args) {

        Student s1 = new Student();

        // setting values using setter methods
        s1.setId(101);
        s1.setName("Sarumathi");

        // getting values using getter methods
        System.out.println("Student ID : " + s1.getId());
        System.out.println("Student Name : " + s1.getName());
    }
}

Output:

POJO Class In Java

S Sarumathi — Tue, 12 May 2026 06:07:06 +0000

A POJO (Plain Old Java Object) is a simple Java class that is not tied to any special frameworks or restrictions. It is mainly used to represent data.

Key Features of a POJO:

Private variables (fields)
Public getter and setter methods
No dependency on external frameworks
May include constructors

Example:

class Student {

    // Private variables
    private int id;
    private String name;

    // Setter methods
    public void setId(int id) {
        this.id = id;
    }

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

    // Getter methods
    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }
}

public class Main {

    public static void main(String[] args) {

        // Object creation
        Student s = new Student();

        // Setting values
        s.setId(101);
        s.setName("Sam");

        // Getting values
        System.out.println("Id : " + s.getId());
        System.out.println("Name : " + s.getName());
    }
}

Output:

Why POJO is Used:

POJO classes are mainly used to:

Store data
Transfer data between layers
Improve code readability
Make programs simple and reusable

Advantages of POJO:

Easy to create
Easy to understand
Reusable
Simple maintenance
Better readability

Method Overriding

S Sarumathi — Fri, 08 May 2026 05:57:06 +0000

Method overriding is one of the most important concepts in Java Object-Oriented Programming (OOP). It allows a child class to provide its own implementation of a method that is already defined in the parent class.

Example of Method Overriding:

class Animal {

    void sound() {
        System.out.println("Animal makes sound");
    }
}

class Dog extends Animal {

    @Override
    void sound() {
        System.out.println("Dog barks");
    }
}

public class Main {

    public static void main(String[] args) {

        Dog d = new Dog();
        d.sound();
    }
}

Output:

Dog barks

Package

S Sarumathi — Tue, 05 May 2026 12:39:32 +0000

What Is Package:
A package in Java is a mechanism used to group related classes, interfaces, and sub-packages. It functions like a folder in a computer file system, providing a unique namespace that prevents naming conflicts between classes with the same name in different libraries. To Be Discussed

Avoiding name conflicts (two classes with the same name can exist in different packages)
Providing access control using public, protected, and default access
Reusability: packaged code can be imported and used anywhere
Encouraging modular programming

Inheritance In Java

S Sarumathi — Sat, 02 May 2026 05:23:48 +0000

1. What is Inheritance in Java:
In Java, Inheritance is one of the core concepts of Object-Oriented Programming (OOP). It allows one class to acquire the properties and methods of another class, promoting code reusability and better organization.

Syntax of Inheritance:

class Parent {
   ** // properties and methods**
}

class Child extends Parent {
    **// additional features**
}

Example:

class Animal {
    void sound() {
        System.out.println("Animal makes sound");
    }
}

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

public class Main {
    public static void main(String[] args) {
        Dog d = new Dog();

        d.sound(); **// inherited method**
        d.bark();  **// own method**
    }
}

Types of Inheritance in Java:

- Single Inheritance
One parent → One child

- Multilevel Inheritance
Grandparent → Parent → Child

- Hierarchical Inheritance
One parent → Multiple children

Java does not support multiple inheritance using classes (to avoid complexity)

Advantages of Inheritance:

Code reusability
Reduces redundancy
Improves maintainability
Supports method overriding

Python Program

S Sarumathi — Tue, 21 Apr 2026 17:23:06 +0000

1. Remove Extra Space:

name="practice makes    perfect"
i=0
result=""
while i<len(name):
  if name[i]!=" ":
    result=result+name[i]
  else:
    if i>0 and name[i-1]!=" ":
      result=result+name[i]
  i+=1
print(result)

Output:

2. Remove Front Space:

name = "     practice makes perfect"
i = 0
result = ""

while i < len(name):
    if name[i] != " ":
        break   
    i += 1

while i < len(name):
    result += name[i]
    i += 1

print(result)

Output:

3.Remove Back Space:

name = "Kill them with your success        "
result = ""

i = len(name)-1

while i >= 0:

    if name[i] == " ":
        i -= 1
        continue

    else:
        j = 0

        while j <= i:
            result += name[j]
            j += 1

        break

print(result)

Output:

4.Reverse The Word:

name = "PULIKESI"
result = ""

i = len(name)-1

while i >= 0:
    result = result + name[i]
    i -= 1

print(result)

Output:

String Program

S Sarumathi — Tue, 21 Apr 2026 08:30:42 +0000

1.Full String Uppercase:

text=input("Enter some words :")
i=0
upper=""
while i<len(text):
    ch=text[i]
    if ch>="a" and ch<="z":
        upper=upper+chr(ord(ch) - 32)
    else:
        upper=upper+ch
    i+=1
print(upper)

Output:

2.Firts Letter Uppercase:

text=input("Enter some words :")
i=0
upper=""
while i<len(text):
    ch=text[i]
    if (ch>="a" and ch<="z") and (text[i-1]==" " or i==0):
        upper=upper+chr(ord(ch) - 32)
    else:
        upper=upper+ch
    i+=1
print(upper)

Output:

3.Letters Count:

text=input("Enter some words :")
i=0
count=0
while i<len(text):
    ch=text[i]
    if (ch>="a" and ch<="z") or (ch>="A" and ch<="Z"):
        count+=1
    i+=1
print(count)

Output:

4.Word Count:

text=input("Enter some words :")
i=0
count=1
while i<len(text):
    if text[i]!=" " and text[i-1]==" ":
        count+=1
    i+=1
print(count)

Output:

5.Password Verify:

text=input("Create your password :")
i=0
upper=False
lower=False
number=False
special=False
others=True
while i<len(text):
    ch=text[i]
    if ch>="A" and ch<="Z":
        upper=True
    elif ch>="a" and ch<="z":
        lower=True
    elif ch>="0" and ch<="9":
        number=True
    elif ch=="!" or ch=="@" or ch=="#" or ch=="$" or ch=="&":
        special=True
    else:
        others=False
    i+=1
if upper and lower and number and special and others:
    print("password succesfully create")
else:
    print("invalied try another")

Output:

5.Password Generator:

import random

upper="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
lower="abcdefghijklmnopqrstuvwxyz"
numbers="0123456789"
special="!@#$&"

all_chars=upper+lower+numbers+special

password=""

password=password+random.choice(upper)
password=password+random.choice(lower)
password=password+random.choice(numbers)
password=password+random.choice(special)

i=4

while i<8:
    password=password+random.choice(all_chars)
    i+=1

print("Generated Password :",password)

Output:

Pincode Finder

S Sarumathi — Mon, 20 Apr 2026 09:01:05 +0000

regions = {
    1: "Delhi",
    2: "Uttar Pradesh & Uttarakhand",
    3: "Rajasthan & Gujarat",
    4: "Maharashtra",
    5: "Andhra Pradesh & Telangana",
    6: "Tamil Nadu & Kerala",
    7: "West Bengal & North East",
    8: "Bihar & Jharkhand",
    9: "Army Postal Service"
}

sub_regions = {
    11: "Delhi Region",
    40: "Mumbai Region",
    60: "Chennai Region",
    70: "Kolkata Region"
}

districts = {
    110: "Delhi",       111: "Delhi (North)",      112: "Delhi (South)",
    400: "Mumbai",      401: "Mumbai (Suburban)",   402: "Mumbai (West)",
    600: "Chennai",     601: "Tiruvallur",          602: "Kanchipuram",
    700: "Kolkata",     701: "Kolkata (North)",     702: "Kolkata (South)"
}

def get_pincode_details(pincode):
    if not pincode.isdigit() or len(pincode) != 6:
        print("Invalid pincode. Enter exactly 6 digits.")
        return

    num         = int(pincode)
    first_digit = num // 100000
    first_two   = num // 10000
    first_three = num // 1000

    print("Region:     ", regions.get(first_digit,   "Unknown"))
    print("Sub-region: ", sub_regions.get(first_two, "Unknown"))
    print("District:   ", districts.get(first_three, "Unknown"))

# ✅ User input
pincode = input("Enter Pincode: ").strip()
get_pincode_details(pincode)

Output:

Constructor Program In Java

S Sarumathi — Sun, 19 Apr 2026 16:24:33 +0000

public class Shopp {
    String Name;
    int price;
    boolean discountavail;
    int discountper;

    public Shopp(String Name, int price, boolean discountavail, int discountper) {
        this.Name = Name;
        this.price = price;
        this.discountavail = discountavail;
        this.discountper = discountper;
    }

    public static void main(String[] args) {
        Shopp P1 = new Shop("Chocolate", 150, false, 0);
        Shopp P2 = new Shop("Rice", 150, true, 20);
        Shopp P3 = new Shop("Oil", 150, true, 15);
        Shopp P4 = new Shop("Ghee", 150, false, 0);

        P1.buy();
        P2.buy();
        P3.buy();
        P4.buy();
    }

    public boolean discount() {
        return discountavail;
    }

    public int finalPrice() {
        if (discount()) {
            return price - (price * discountper / 100);
        } else {
            return price;
        }
    }

    public void buy() {
        System.out.println("Name: " + Name);
        System.out.println("Price: " + price);
        System.out.println("Discount Available: " + discountavail);
        System.out.println("Discount Percentage: " + discountper);

        if (discount()) {
            System.out.println("Discount Applied: " + discountper + "%");
        }

        System.out.println("Final Price: " + finalPrice());

    }
}

Output:

Pincode, Gmail, Mobile Number Validation Program

S Sarumathi — Fri, 17 Apr 2026 17:18:34 +0000

Pincode Validation:

pincode = int(input("Enter a pincode: "))

count = 0
temp = pincode

while temp > 0:
    temp = temp // 10
    count += 1

if count == 6 and pincode >= 100000 and pincode <= 999999:
    print("YES")
else:
    print("NO")

Output:

Gmail Validation:

def verify_Gmail(Gmail):
    i=0
    while i<len(Gmail):
        current=Gmail[i]
        i+=1
        if current>="a" and current<="z":
            continue;
        elif current>="A" and current<="Z":
            continue;
        elif current>="0" and current<="9":
            continue;
        elif current=="@" or current=="." or current=="_":
            continue;
        else:
            return False
    if Gmail[-10:]=="@gmail.com":
        return True
    else:
        return False
if verify_Gmail(input("Enter Your Gmail :")):
    print("valid")
else:
    print("invalid")

Output:

Mobile Number Validation:

def mobile(n):
    i=0
    while i<len(n):
        if(n[i]>="0" and n[i]<="9") or (n[i]=="+") or (n[i]==" "):
            i+=1
        else:
            return "characters and special charactors not allowed"

    if len(n)==10:
        if n[0]>="6" and n[0]<="9":
            return "valid";
        else:
            return "First number should not be less then 6 "
    if len(n)==13:
        if n[0:3]=="+91":
            if n[3]>="6" and n[3]<="9":
                return "valid"
            else:
                return "Fourth number should not be less then 6"
        else:
            return "First three number should like +91"
    if len(n)==14:
        if n[0:4]=="+91 ":
            if n[4]>="6" and n[4]<="9":
                return "valid"
            else:
                return "fifth number should not be less then 6"
        return "First four number should like +91 "
    return "Please Enter Your valid Mobile Number"      
print(mobile(input("Enter Your Mobile  Number : ")));

Output:

To Be Discussed....