DEV Community: Ezhil Abinaya K

StringBuffer in Java

Ezhil Abinaya K — Thu, 24 Sep 2026 06:45:37 +0000

StringBuffer
StringBuffer class in Java represents a sequence of characters that can be modified, which means we can change the content of the StringBuffer without creating a new object every time. It represents a mutable sequence of characters.
append(char c)
It appends the string representation of the char argument to this sequence.

public class StringBufferDemo {
    public static void main(String[] args){

        // Creating StringBuffer
        StringBuffer s = new StringBuffer();

        // Adding elements in StringBuffer
        s.append("Hello");
        s.append(" ");
        s.append("world");

        // String with the StringBuffer value
        String str = s.toString();
        System.out.println(str);
    }
}
//Hello world

insert() Method
insert() method inserts the given string with this string at the given position.

 s.insert(1, "Java");
 System.out.println(s); // HJavaello world

replace()
replace() method replaces the given string from the specified beginIndex and endIndex-1.

   StringBuffer sb = new StringBuffer("Hello");
        sb.replace(1, 3, "i"); 
        System.out.println(sb);
//Hilo

delete()
delete() method is used to delete the string from the specified beginIndex to endIndex-1.

sb.delete(1, 3);
 System.out.println(sb);//Ho

reverse()
reverse() method of the StringBuffer class reverses the current string.

sb.reverse();
 System.out.println(sb);//oH

Reference
https://www.geeksforgeeks.org/java/stringbuffer-class-in-java/
https://docs.oracle.com/javase/8/docs/api/java/lang/StringBuffer.html

String Methods in Java

Ezhil Abinaya K — Wed, 23 Sep 2026 05:02:42 +0000

charAt()
The charAt() method returns the character at the specified index in a string.The index of the first character is 0, the second character is 1, and so on.It throws IndexOutOfBoundsException - if index is negative or not less than the length of the specified string.
Syntax

public char charAt(int index)

public class Main {
  public static void main(String[] args) {
    String myStr = "Hello";
    char result = myStr.charAt(0);
    System.out.println(result);
  }
}
// H

concat()
concat(String str)
It Concatenates the specified string to the end of this string.It returns a String, representing the text of the combined strings.

String firstName = "John ";
String lastName = "Doe";
System.out.println(firstName.concat(lastName));
//John Doe

contains
(CharSequence s)
The contains() method checks whether a string contains a sequence of characters.It returns true if the characters exist and false if not. It throws NullPointerException - if the returned value is null.It return type is boolean.

String myStr = "Hello";
System.out.println(myStr.contains("Hel"));   // true
System.out.println(myStr.contains("e"));     // true
System.out.println(myStr.contains("Hi"));    // false

isEmpty()
The isEmpty() method checks whether a string is empty or not. It returns true if, and only if, length() is 0.It return data type is boolean.

String myStr1 = "Hello";
String myStr2 = "";
System.out.println(myStr1.isEmpty());
System.out.println(myStr2.isEmpty());
//false
true

length()
It returns the length of this string.It returns value is int.

String txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
System.out.println(txt.length());
//26

equals(Object anObject)
It Compares this string to the specified object.compares two strings, and returns true if the strings are equal, and false if not.
anObject = An Object, representing the other string to be compared

String myStr1 = "Hello";
String myStr2 = "Hello";
String myStr3 = "Another String";
System.out.println(myStr1.equals(myStr2)); // Returns true because they are equal
System.out.println(myStr1.equals(myStr3)); // false

replace(char oldChar, char newChar)
The replace() method searches a string for a specified character, and returns a new string where the specified character(s) are replaced.

String myStr = "Hello";
System.out.println(myStr.replace('l', 'p'));
//Heppo

split(String regex)
It splits this string around matches of the given regular expression. it returns String[].
regex= Required. A regular expression defining the separators where the string is split.

String myStr = "Split a string by spaces, and also punctuation.";
String regex = "[,\\.\\s]";
String[] myArray = myStr.split(regex);
for (String s : myArray) {
  System.out.println(s);
}
//Split
a
string
by
spaces

and
also
punctuation

References
https://www.w3schools.com/java/ref_string_split.asp
https://docs.oracle.com/javase/8/docs/api/java/lang/String.html

My First Tech Talk at Kanchi Linux Users Group

Ezhil Abinaya K — Sun, 20 Sep 2026 12:55:41 +0000

I’m happy to share that I recently had the opportunity to give my first tech talk as a speaker.Preparing for the talk itself taught me a lot about structuring content, communicating clearly, and speaking with confidence.A small technical issue meant that my slides were not visible in the recording, but the experience of delivering the talk was truly valuable. 😊

Thank you to everyone who gave me this opportunity and supported me. [(https://www.youtube.com/live/wapddlEulUA?si=PXIrSqQgySammkEP)]

File Handling in java

Ezhil Abinaya K — Tue, 15 Sep 2026 13:22:10 +0000

File Handling
In Java, file handling means working with files like creating them, reading data, writing data or deleting them. It helps a program save and use information permanently on the computer.

Main.java

package com.payilagam.controller;
import java.util.ArrayList;
import com.payilagam.service.Studentservice;
import com.payilagam.entity.Student;
import java.io.File;
import java.io.IOException;
import java.io.FileReader;
import java.io.FileNotFoundException;
public class Main{
public static void main(String[] args){
 File location = new File("/home/ezhil-abinaya-k/prp/java");

        File[] files = location.listFiles();

        for (File file : files) {
            System.out.println(file.getName());
        }
        for (File file : files) {
    if (file.isFile()) {
        System.out.println("File: " + file.getName());
    } else {
        System.out.println("Folder: " + file.getName());
    }
}
File file=new File("Ezhil.csv");
try{
  boolean created =file.createNewFile();
  System.out.println("created file");
  }catch(IOException io){
  System.out.println("Exception error");
}
try{
   FileReader reader=new FileReader(file);
   int i =reader.read();
   while(i!=-1){
  System.out.print((char)i);
  i=reader.read();
  }


}catch(FileNotFoundException obj){
    System.out.println("error-obj");
}
catch(IOException io){
  System.out.println("error-io");
}

}
}
Output:
Main.java
Supermarket.java
Studentservice.java
Student.class
Home.class
com
Studentservice.class
Main.class
Supermarket.class
Home.java
.git
Ezhil.csv
Student.java
File: Main.java
File: Supermarket.java
File: Studentservice.java
File: Student.class
File: Home.class
Folder: com
File: Studentservice.class
File: Main.class
File: Supermarket.class
File: Home.java
Folder: .git
File: Ezhil.csv
File: Student.java
created file
id,name,mark,course
1, Ezhil,java,90
2, Saru, python, 90
3, Kamali, react,88

Student.java

package com.payilagam.entity;
public class Student{
private int id;
private String name;
private String course;
private int mark;
public Student (int id, String name, String course, int mark){
 this.id=id;
 this.name=name;
 this.course=course;
 this.mark=mark;
}
public static void main(String[] args){

}
public int getId(){
return id;
}
public void setId(int id){
this.id=id;
}
public String getName(){
return name;
}
public void setName(String name){
this.name=name;
}
public String getCourse(){
return course;
}
public void setCourse(String course){
this.course=course;
}
public int getMark(){
return mark;
}
public void setMark(int mark){
this.mark=mark;
}
}

Studentservice.java

package com.payilagam.service;
import java.util.ArrayList;
import com.payilagam.entity.Student;
public class Studentservice {

    ArrayList<Student> students = new ArrayList<>();

    // Add Student
    public void addStudent(Student stud) {
        boolean addStatus=students.add(stud);
        if (addStatus){
        System.out.println("added success");
        } else{
        System.out.println("something went wrong");
        }
    }

    // View Students
    public ArrayList<Student> viewStudent() {
    for(Student student:students){
System.out.println(student.getId()+"-"+student.getName()+"-"+student.getCourse()+"-"+student.getMark());
 }
 return students;
 }

    // Search Student
    public void searchStudent(int id) {
    boolean found=false;
    for(Student student:students){
    if(student.getId()==id){
    System.out.println(student.getId()+"-"+student.getName()+"-"+student.getCourse()+"-"+student.getMark());found=true;
    }
    }if(found==false){
    System.out.println("not found...");
    }

        }



    // Update Student Mark
   public void updateStudent(int id, int newMark) {
    for(Student student : students) {
        if(student.getId() == id) {
            student.setMark(newMark);
            System.out.println("student updated successfully");
            return;
        }
    }
    System.out.println("student not found...");
}

    // Delete Student
    public void deleteStudent(int id) {
    boolean found=false;
    for (Student student:students){
    if(student.getId()==id){
    students.remove(student);
    System.out.println("student deleted successfully");
    found=true;
    break;
    }
    } 
    if(found==false){
    System.out.println("student not found...");
    }

    }


}

Reference
https://www.geeksforgeeks.org/java/file-handling-in-java/

String DataType in Python

Ezhil Abinaya K — Sat, 05 Sep 2026 13:31:47 +0000

String
Strings are sequence of characters written inside quotes. It can include letters, numbers, symbols and spaces. Python does not have a separate character type.Strings are immutable.
Immutable means changes are updated in new memory. Existing memory won't affect. Mutable means existing memory can change.
Garbage Collection
Garbage collector will automatically removed unused object from memory.

name="Ezhil"
print(name)
name="K Ezhil"
print(name) #here, garbage collecor is happened.

name="Ezhil"
print(type(name))
print(id(name))
name="K Ezhil"
print(id(name))
O/P:
<class 'str'>
134810544205488
134810544206304

print(hash(name))
O/P:
print(hash(name))

name="Ezhil Abinaya"
print(len(name))
i=0
while i<len(name):
      print(name[i], end='')
      i+=1
print()
O/P:
13
Ezhil Abinaya

name="Ezhil"
print(name[0])
print(name[1])
print(name[-1])
print(name[-2])
o/p:
E
z
l
i

name="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
print(name[0:26]) #slicing operator
print(name[0:26:3]) #[start:stop:step]
print(name[:]) #all print
print(name[::2])
print(name[5:10])
O/P:
ABCDEFGHIJKLMNOPQRSTUVWXYZ
ADGJMPSVY
ABCDEFGHIJKLMNOPQRSTUVWXYZ
ACEGIKMOQSUWY
FGHIJ

alpha="madam"
print(alpha[::-1]==alpha) # reverse a palindrome
O/P:
True

Student Management Service in Java

Ezhil Abinaya K — Fri, 04 Sep 2026 13:48:59 +0000

I have practiced a Student management service project in java.
Student.java

public class Student{
private int id;
private String name;
private String course;
private int mark;
public Student (int id, String name, String course, int mark){
 this.id=id;
 this.name=name;
 this.course=course;
 this.mark=mark;
}
public static void main(String[] args){

}
public int getId(){
return id;
}
public void setId(int id){
this.id=id;
}
public String getName(){
return name;
}
public void setName(String name){
this.name=name;
}
public String getCourse(){
return course;
}
public void setCourse(String course){
this.course=course;
}
public int getMark(){
return mark;
}
public void setMark(int mark){
this.mark=mark;
}
}

Studentservice.java

import java.util.ArrayList;

public class Studentservice {

    ArrayList<Student> students = new ArrayList<>();

    // Add Student
    public void addStudent(Student stud) {
        boolean addStatus=students.add(stud);
        if (addStatus){
        System.out.println("added success");
        } else{
        System.out.println("something went wrong");
        }
    }

    // View Students
    public ArrayList<Student> viewStudent() {
    for(Student student:students){
System.out.println(student.getId()+"-"+student.getName()+"-"+student.getCourse()+"-"+student.getMark());
 }
 return students;
 }

    // Search Student
    public void searchStudent(int id) {
    boolean found=false;
    for(Student student:students){
    if(student.getId()==id){
    System.out.println(student.getId()+"-"+student.getName()+"-"+student.getCourse()+"-"+student.getMark());found=true;
    }
    }if(found==false){
    System.out.println("not found...");
    }

        }



    // Update Student Mark
    public void updateStudent(int id, int newMark) {
    boolean found=false;
    for(Student student:students){
    if(student.getId()==id){
    student.setMark(newMark);
    System.out.println("mark updated successfully");
    found=true;
    }
    }
    if(found==false){
    System.out.println("student not found..");
    }

    }

    // Delete Student
    public void deleteStudent(int id) {
    boolean found=false;
    for (Student student:students){
    if(student.getId()==id){
    students.remove(student);
    System.out.println("student deleted successfully");
    found=true;
    break;
    }
    } 
    if(found==false){
    System.out.println("student not found...");
    }

    }


}

Main.java

import java.util.ArrayList;
public class Main{
public static void main(String[] args){
Student s1= new Student(101,"Ezhil","java",92);
Student s2= new Student(102,"Akila", "python", 90);
Student s3=new Student(103,"Saru","R",90);
Studentservice service=new Studentservice();
service.addStudent(s1);
service.addStudent(s2);
service.addStudent(s3);
//service.viewStudent();//
service.searchStudent(101);
service.searchStudent(102);
service.updateStudent(101,95);
service.viewStudent();
service.deleteStudent(103);
service.viewStudent();

//ArrayList<Student>students=service.viewStudent();//


}
}
O/P:
added success
added success
added success
101-Ezhil-java-92
102-Akila-python-90
mark updated successfully
101-Ezhil-java-95
102-Akila-python-90
103-Saru-R-90
student deleted successfully
101-Ezhil-java-95
102-Akila-python-90

Python Pattern Program

Ezhil Abinaya K — Wed, 02 Sep 2026 13:43:05 +0000

for i in range(0, 5):
    for j in range(0, i+1):
        print("* ",end="")
    print()
o/p:
* 
* * 
* * * 
* * * * 
* * * * *

plaintext
2)

for i in range(5, 0, -1):
    for j in range(i):
        print("* ", end="")
    print()
o/p:
* * * * 
* * * 
* * 
*

Getter ,Setter in Java

Ezhil Abinaya K — Tue, 01 Sep 2026 15:01:33 +0000

In Java, Getter and Setter are methods used to protect your data and make your code more secure. Getter and Setter make the programmer convenient in setting and getting the value for a particular data type.

Getter in Java: Getter returns the value (accessors), it returns the value of data type int, String, double, float, etc. For the program's convenience, the getter starts with the word "get" followed by the variable name.

Setter in Java: While Setter sets or updates the value (mutators). It sets the value for any variable used in a class's programs. and starts with the word "set" followed by the variable name.

public class Student{
//private variables and getter setter method =pojo
private int id;
private String name;
private String course;
private int mark;
public Student(int id, String name, String course, int mark) {
        this.id = id;
        this.name = name;
        this.course = course;
        this.mark = mark;
    }
public static void main(String[] args){
Student s1 = new Student(101, "Ezhil", "Java", 85);
Student s2 = new Student(102, "Anban", "Python", 92);
}
public int getId() {
        return id;
 }

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

 public String getName() {
        return name;
 }

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

public String getCourse() {
        return course;
}

public void setCourse(String course) {
        this.course = course;
}

public int getMark() {
        return mark;
}

 public void setMark(int mark) {
        this.mark = mark;
}
}

Reference
https://www.geeksforgeeks.org/java/getter-and-setter-in-java/

Python Programs: Binary to Decimal and Spy Number

Ezhil Abinaya K — Sat, 29 Aug 2026 15:53:25 +0000

1) Binary to Decimal

binary=int(input(“enter a number:))
decimal=0
power=0
while binary>0:
          digit=binary%10
          decimal=decimal+digit * 2 ** power
          binary=binary//10
          power+=1
print(“decimal=”,decimal)

O/P:enter a number:1011
decimal = 11

2)Spy Number

num=int(input(“enter a number:))
sum_of_digit=0
product=1
while num>0:
          digit=num%10
          sum_of_digit+=1
          product*=1
          num//10
if sum_of_digit==product:
       print(“spy number”)
else:
      print(“not a spy number”)
o/p: enter a number:1124
spy number

Java Basic Concepts

Ezhil Abinaya K — Fri, 28 Aug 2026 14:15:01 +0000

Java this Keyword
The this keyword in Java refers to the current object in a method or constructor.The this keyword is often used to avoid confusion when class attributes have the same name as method or constructor parameters.
Java Classes/Objects
Java is an object-oriented programming language.Everything in Java is associated with classes and objects, along with its attributes and methods. For example: in real life, a car is an object. The car has attributes, such as weight and color, and methods, such as drive and brake.A Class is like an object constructor, or a "blueprint" for creating objects.
OOP stands for Object-Oriented Programming.

Procedural programming is about writing procedures or methods that perform operations on the data, while object-oriented programming is about creating objects that contain both data and methods.OOP is ideal for building scalable, reusable, and maintainable code.

Object-oriented programming has several advantages over procedural programming:

OOP provides a clear structure for the programs
OOP helps to keep the Java code DRY "Don't Repeat Yourself", and makes the code easier to maintain, modify and debug
OOP makes it possible to create full reusable applications with less code and shorter development time.

References
https://www.w3schools.com/java/java_oop.asp
https://www.w3schools.com/java/java_oop.asp

Methods in Java

Ezhil Abinaya K — Thu, 27 Aug 2026 13:59:55 +0000

Methods
A method is a block of code which only runs when it is called.You can pass data, known as parameters, into a method.Methods are used to perform certain actions, and they are also known as functions.
Why use methods? To reuse code: define the code once, and use it many times.
Create a Method
A method must be declared within a class. It is defined with the name of the method, followed by parentheses (). Java provides some pre-defined methods, such as System.out.println(), but you can also create your own methods to perform certain actions.

//Create a method inside Main://

public class Geeks
{
    // An example method
    public void printMessage() {
        System.out.println("Hello, Geeks!");
    }

    public static void main(String[] args) {

        // Create an instance of the class
        // containing the method
        Geeks obj = new Geeks();

        // Calling the method
        obj.printMessage(); 
    }
}
O/P:
Hello, Geeks!

Syntax of Java Methods

returnType methodName(parameters) {
  // method body
 return value; // optional (only if returnType is not void)
}

Method Overloading
Same method name with different number of arguments or with diiferent type of arguments are called method overloading or compile time polymorphism.

public class Supermarket
{
//fields
static String supermarketname="D-Mart";
static int supermarketdoorno=13/1;
//non-static variables
String things;
int price;
int discount;
public Supermarket(String things,int price){
this.things=things;
this.price=price;
}
public Supermarket(String things,int price,int discount){
this.things=things;
this.price=price;
this.discount=discount;
}
public static void main(String[] args)
{
//object
Supermarket things1=new Supermarket("Rosemilk",30);
Supermarket things2=new Supermarket("Galaxychocky",50);
Supermarket things3=new Supermarket("Kinderjoy",50,20);
things1.buy();
things1.buy(10);
 System.out.println(Supermarket.supermarketname);
 System.out.println(Supermarket.supermarketdoorno);
 System.out.println(things1.things);
 System.out.println("₹" + things1.price);
 System.out.println(things2.things);
 System.out.println("₹" + things2.price);
 System.out.println(things3.things);
 System.out.println("₹" + things3.price);
  System.out.println(things3.discount + "%" );
 }
 //method overloading
 public void buy(){
 System.out.println("buy-method");
 }
 public void buy(int account){
 System.out.println("buy-method-one-argument");
 }
}
o/p:
buy-method
buy-method-one-argument
D-Mart
13
Rosemilk
₹30
Galaxychocky
₹50
Kinderjoy
₹50
20%

References
https://www.w3schools.com/java/java_methods.asp
https://www.geeksforgeeks.org/java/methods-in-java/

Constructors in Java

Ezhil Abinaya K — Wed, 26 Aug 2026 14:39:19 +0000

Java Constructors
A constructor in Java is a special member that is called when an object is created. It initializes the new object’s state. It is used to set default or user-defined values for the object's attributes

A constructor has the same name as the class.
It does not have a return type, not even void.
It can accept parameters to initialize object properties.

public class Home
{
//fields
static String homename="Ezhil";
static int homeAge=15;
//non-static variables
String name;
int age;
//constructor
public Home(String name,int age){
this.name=name;
this.age=age;
}

public static void main(String[] args)
{
//object
Home person1=new Home("Anban",30);
Home person2=new Home("Karthikeyan",55);
 System.out.println(Home.homename);
 System.out.println(Home.homeAge);
 System.out.println(person1.name);
 System.out.println(person1.age);
 System.out.println(person2.name);
 System.out.println(person2.age);
 }
}
O/P:
Ezhil
15
Anban
30
Karthikeyan
55

public class Supermarket
{
//fields
static String supermarketname="D-Mart";
static int supermarketdoorno=13/1;
//non-static variables
String things;
int price;
int discount;
public Supermarket(String things,int price){
this.things=things;
this.price=price;
}
public Supermarket(String things,int price,int discount){
this.things=things;
this.price=price;
this.discount=discount;
}
public static void main(String[] args)
{
//object
Supermarket things1=new Supermarket("Rosemilk",30);
Supermarket things2=new Supermarket("Galaxychocky",50);
Supermarket things3=new Supermarket("Kinderjoy",50,20);
 System.out.println(Supermarket.supermarketname);
 System.out.println(Supermarket.supermarketdoorno);
 System.out.println(things1.things);
 System.out.println("₹" + things1.price);
 System.out.println(things2.things);
 System.out.println("₹" + things2.price);
 System.out.println(things3.things);
 System.out.println("₹" + things3.price);
  System.out.println(things3.discount + "%" );
 }
}
0/P:
D-Mart
13
Rosemilk
₹30
Galaxychocky
₹50
Kinderjoy
₹50
20%

Reference
https://www.geeksforgeeks.org/java/constructors-in-java/