DEV Community: Saravanan Lakshmanan

Java Learning Series - Finding Unique and Duplicate categories using HashSet

Saravanan Lakshmanan — Wed, 23 Sep 2026 18:16:21 +0000

    public HashSet<String> findUniqueCategory(){
        ArrayList<Product> arr = dao.viewProduct();
        //container to add only unique category to avoid duplication
        HashSet<String> set = new HashSet();

        for(Product product : arr){
            set.add(product.getCategory());
        }
    return set;
    }

    public HashSet<String> findUniqueDuplicateCategory(){

        ArrayList<Product> arr = dao.viewProduct();
        HashSet<String> set = new HashSet();

        for(Product product : arr){
            if(set.add(product.getCategory())){
                System.out.println("Unique Category: "+ product.getCategory());
            }else{
                System.out.println("Duplicate Category: "+ product.getCategory());
            }
        }
    return set;
    }

    public HashSet<String> findDuplicateUniqueCategory(){

        ArrayList<Product> arr = dao.viewProduct();
        HashSet<String> uniqueSet = new HashSet();
        HashSet<String> duplicateSet = new HashSet();

        for(Product product : arr){
            boolean unique = uniqueSet.add(product.getCategory());
            if(!unique){
                duplicateSet.add(product.getCategory());
            }
        }
    return duplicateSet;
    }

Output:

SQL is Connected
[3-Laptop-Electronics-50000, 2-Ipad-Electronics-40000, 1-Chair-Furniture-10000, 4-Shirt-Clothing-1000, 5-Pant-Clothing-2000]
SQL is Connected
[]
SQL is Connected
[Clothing, Electronics, Furniture]
SQL is Connected
Unique Category: Electronics
Duplicate Category: Electronics
Unique Category: Furniture
Unique Category: Clothing
Duplicate Category: Clothing
[Clothing, Electronics, Furniture]
SQL is Connected
[Clothing, Electronics]

Java Learning Series - Updated Product Management System with a DAO class

Saravanan Lakshmanan — Mon, 21 Sep 2026 19:31:27 +0000

Product.java

package com.company.entity;

public class Product{

    private int id;
    private String name;
    private String category;
    private int price;

    public Product(int id, String name, String category, int price){
        this.id = id;
        this.name = name;
        this.category = category;
        this.price = price;
    }

//    Product p1 = new Product(int id, String name, String category, int price);

    public int getId(){
        return this.id;
    }

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

    public String getName(){
        return this.name;
    }

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

    public String getCategory(){
        return this.category;
    }

    public void setCategory(String category){
        this.category = category;
    }

    public int getPrice(){
        return this.price;
    }

    public void setPrice(int price){
        this.price = price;
    }

    @Override
    public String toString(){
        return this.getId() + "-" + this.getName() + "-" + this.getCategory() + "-" + this.getPrice();
    }


}

DBConnection.java

package com.company.db;
import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.SQLException;

public class DBConnection{

    public static Connection getPSQLConnection(){
        Connection con = null;
        try{
            String url = "jdbc:postgresql://localhost:5432/productdb";
            String username = "postgres";
            String password = "saravanan";

            con = DriverManager.getConnection(url, username, password);
            System.out.println("SQL is Connected");

        }catch(SQLException exe){
            System.out.println(exe.getMessage());
        }

    return con;
    }

}

ProductDAO.java

package com.company.dao;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.sql.SQLException;
import com.company.entity.Product;
import com.company.db.DBConnection;

public class ProductDAO{

    public void addProduct(Product product){

        try{
            Connection con = DBConnection.getPSQLConnection();
            String sql = "insert into products values(?,?,?,?)";
            PreparedStatement ps = con.prepareStatement(sql);
            ps.setInt(1,product.getId());
            ps.setString(2,product.getName());
            ps.setString(3,product.getCategory());
            ps.setInt(4,product.getPrice());

            int row = ps.executeUpdate();
            System.out.println(row + " product added");
        }catch(SQLException exe){
            System.out.println(exe.getMessage());
        }

    }

    public ArrayList<Product> viewProduct(){

            ArrayList<Product> arr = new ArrayList();

        try{
            Connection con = DBConnection.getPSQLConnection();

            String sql = "select * from products";

            PreparedStatement ps = con.prepareStatement(sql);
            ResultSet rs = ps.executeQuery();

            while(rs.next()){
                int id = rs.getInt("id");
                String name = rs.getString("name");
                String category = rs.getString("category");
                int price = rs.getInt("price");

            Product p = new Product(id, name, category, price);
            arr.add(p);
            }
        }catch(SQLException exe){
            System.out.println(exe.getMessage());
        }
    return arr;
    }

    public void updateProduct(Product product){

    try{
            Connection con = DBConnection.getPSQLConnection();
            String sql = "update products set name = ?, category = ?, price = ? where id = ?";
            PreparedStatement ps = con.prepareStatement(sql);
            ps.setString(1,product.getName());
            ps.setString(2,product.getCategory());
            ps.setInt(3,product.getPrice());
            ps.setInt(4,product.getId());
            int updateStatus = ps.executeUpdate();
            System.out.println(updateStatus);

            if(updateStatus > 0){
                System.out.println("Product is Updated");
            }else{
                System.out.println("Product is Not Updated");
            }    
        }catch(SQLException exe){
                System.out.println(exe.getMessage());
        }

    }

    public void deleteProduct(int id){

    try{
            Connection con = DBConnection.getPSQLConnection();
            String sql = "delete from products where id = ?";
            PreparedStatement ps = con.prepareStatement(sql);
            ps.setInt(1,id);
            int deleteStatus = ps.executeUpdate();
            System.out.println(deleteStatus);

            if(deleteStatus > 0){
                System.out.println("Product is Deleted");
            }else{
                System.out.println("Product is Not Found");
            }
        }catch(SQLException exe){
            System.out.println(exe.getMessage());
        }

    }

}

ProductService.java

package com.company.service;
import com.company.dao.ProductDAO;
import com.company.entity.Product;
import java.util.ArrayList;

public class ProductService{

    ProductDAO dao = new ProductDAO();

    public void addProduct(Product product){
        dao.addProduct(product);
    }

    public ArrayList<Product> viewProduct(){
        return dao.viewProduct();
    }

    public void updateProduct(Product product){
        dao.updateProduct(product);
    }

    public void deleteProduct(int id){
        dao.deleteProduct(id);
    }

    public Product findTopPrice(){
        ArrayList<Product> arr = dao.viewProduct();
        Product topPrice = arr.get(0);

        for(Product product : arr){
            if(topPrice.getPrice() < product.getPrice()){
                 topPrice = product;
            }
        }
    return topPrice;
    }

}

Main.java

package com.company.controller;
import com.company.dao.ProductDAO;
import com.company.entity.Product;
import java.util.ArrayList;
import com.company.service.ProductService;


public class Main{

    public static void main(String[] args){

        ProductDAO dao = new ProductDAO();
        ArrayList<Product> arr = dao.viewProduct();
        System.out.println(arr);
        Product p = new Product(1,"Chair","Furniture",10000);
//        dao.addProduct(p);

        arr = dao.viewProduct();
        System.out.println(arr);

        ProductService service = new ProductService();
        Product p1 = service.findTopPrice();
        System.out.println(p1);

    }

}

Output:

SQL is Connected
[3-Laptop-Electronics-50000, 2-Ipad-Electronics-40000, 1-Chair-Furniture-10000]
SQL is Connected
[3-Laptop-Electronics-50000, 2-Ipad-Electronics-40000, 1-Chair-Furniture-10000]
SQL is Connected
3-Laptop-Electronics-50000

Java Learning Series - Product Management System with CRUD operations for beginners

Saravanan Lakshmanan — Sun, 20 Sep 2026 19:23:19 +0000

Product.java

package com.company.entity;

public class Product{

    private int id;
    private String name;
    private String category;
    private int price;

    public Product(int id, String name, String category, int price) {
        this.id = id;
        this.name = name;
        this.category = category;
        this.price = price;
    }

    public int getId() {
        return this.id;
    }

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

    public String getName() {
        return this.name;
    }

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

    public String getCategory() {
        return this.category;
    }

    public void setCategory(String category) {
        this.category = category;
    }

    public int getPrice() {
        return this.price;
    }

    public void setPrice(int price) {
        this.price = price;
    }

    public String toString() {
        return this.getId() + " , " + this.getName() + " , " + this.getCategory() + " , " + this.getPrice();
    }
}

ProductService.java

package com.company.service;
import com.company.entity.Product;
import com.company.db.DBConnection;
import java.sql.Connection;
import java.sql.DriverManager;
import java.util.ArrayList;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class ProductService{

    ArrayList<Product> arr = new ArrayList();

    public void addProduct(Product product) {
        try{
            Connection con = DBConnection.getPSQLConnection();
        String sql = "insert into products values(?,?,?,?)";
        PreparedStatement ps = con.prepareStatement(sql);
            ps.setInt(1, product.getId());
            ps.setString(2,product.getName());
            ps.setString(3,product.getCategory());
            ps.setInt(4,product.getPrice());
        int row = ps.executeUpdate();
            System.out.println(row);
        }catch(SQLException exe_obj){
            System.out.println(exe_obj.getMessage());
        }

//        boolean addStatus = arr.add(product);
//        if (addStatus) {
//            System.out.println("Product is Added");
//        } else {
//            System.out.println("Product is not Added");
//        }
    }

    public ArrayList<Product> viewProduct() {
//        for (Product product : arr) {
//            System.out.println(product);
//        }
//            arr.clear();
            try{
                Connection con = DBConnection.getPSQLConnection();
                String sql = "select * from products";
                PreparedStatement ps = con.prepareStatement(sql);
//                System.out.println(ps);
                ResultSet rs = ps.executeQuery();
//                System.out.println(rs);
                while(rs.next()){     //next() - is used to read data(row by row)
//                    System.out.println(rs.getInt("id"));
//                    System.out.println(rs.getString("name"));
//                    System.out.println(rs.getString("category"));
//                    System.out.println(rs.getInt("price"));   
//                if(rs.next()){
//                    System.out.println("Row found");
//                }else{
//                    System.out.println("Row not found");
//                }

                int id = rs.getInt("id");
                String name = rs.getString("name");
                String category = rs.getString("category");
                int price = rs.getInt("price");
                //after reading datas from database. It is converted into Product object
                Product product = new Product(id,name,category,price);
                //storing the object in ArrayList
                arr.add(product);
                }

            }catch(SQLException exe){
                System.out.println("SQLException");
            }
    return arr;
    }

    public void searchProduct(int id) {
        try{
            Connection con = DBConnection.getPSQLConnection();
            String sql = "select * from products where id = ?";
            PreparedStatement ps = con.prepareStatement(sql);
            ps.setInt(1,id);

            ResultSet rs = ps.executeQuery();

            if(rs.next()){
                System.out.println(rs.getInt("id"));
                System.out.println(rs.getString("name"));
                System.out.println(rs.getString("category"));
                System.out.println(rs.getInt("price"));
            }else{
                System.out.println("Product is Not Found");
            }        

        }catch(SQLException exe){
            System.out.println(exe.getMessage());
        }







//        System.out.println();
//        boolean found = false;
//
//        for (Product product : arr) {
//            if (product.getId() == id) {
//                System.out.println(product.getId() + " - " + product.getName() + " - " + product.getCategory() + " - " + product.getPrice());
//                found = true;
//                break;
//            }
//        }
//
//        if (found == true) {
//            System.out.println("Product is Found");
//        } else {
//            System.out.println("Product is not Found");
//        }
    }

    public void updateProduct(Product newProduct) {
        try{
            Connection con = DBConnection.getPSQLConnection();
            String sql = "update products set name = ?, category = ?, price = ? where id = ?";
            PreparedStatement ps = con.prepareStatement(sql);
            ps.setString(1,newProduct.getName());
            ps.setString(2,newProduct.getCategory());
            ps.setInt(3,newProduct.getPrice());
            ps.setInt(4,newProduct.getId());
            int updateStatus = ps.executeUpdate();
            System.out.println(updateStatus);

            if(updateStatus > 0){
                System.out.println("Product is Updated");
            }else{
                System.out.println("Product is Not Updated");
            }    
        }catch(SQLException exe){
                System.out.println(exe.getMessage());
        }

//        for (Product existingProduct : arr) {
//            if (existingProduct.getId() == newProduct.getId()) {
//                existingProduct.setName(newProduct.getName());
//                existingProduct.setCategory(newProduct.getCategory());
//                existingProduct.setPrice(newProduct.getPrice());
//            }
//        }
    }

    public void deleteProduct(int id) {
        try{
            Connection con = DBConnection.getPSQLConnection();
            String sql = "delete from products where id = ?";
            PreparedStatement ps = con.prepareStatement(sql);
            ps.setInt(1,id);
            int deleteStatus = ps.executeUpdate();
            System.out.println(deleteStatus);

            if(deleteStatus > 0){
                System.out.println("Product is Deleted");
            }else{
                System.out.println("Product is Not Found");
            }
        }catch(SQLException exe){
            System.out.println(exe.getMessage());
        }
    }



//        boolean deleteStatus = false;
//
//        for (Product product : arr) {
//            if (product.getId() == id) {
//                arr.remove(product);
//                deleteStatus = true;
//                break;
//            }
//        }
//
//        if (deleteStatus == true) {
//            System.out.println("Product is Deleted");
//        } else {
//            System.out.println("Product is Not Found");
//        }
//    }
}

Main.java

package com.company.controller;
import com.company.entity.Product;
import com.company.service.ProductService;
import java.util.ArrayList;

import java.io.File;
import java.io.FileReader;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.FileNotFoundException;

public class Main{

    public static void main(String[] args) {

        ProductService service = new ProductService();


        Product product = new Product(3,"Laptop","Electronics",50000);
//        service.addProduct(product);

        ArrayList<Product> arr1 = service.viewProduct();
        System.out.println(arr1);
//        service.searchProduct(1);
        service.deleteProduct(1);

        System.out.println(service.viewProduct());   

        System.out.println(service.viewProduct());
        Product p1 = new Product(2,"Ipad","Electronics",40000);
        service.updateProduct(p1);

        System.out.println(service.viewProduct());

        service.searchProduct(3);

//        File file = new File("products.csv");
//        System.out.println(file.canRead());
//        
//        try{
//            FileReader reader = new FileReader(file);
//            BufferedReader br = new BufferedReader(reader);
//            String line = br.readLine();
//
//            line = br.readLine();
//            while(line!=null){
//                String[] data = line.split(",");
//                System.out.println(data);
//                System.out.println(line);
//
//                    int id = Integer.parseInt(data[0]);
//                    String name = data[1];
//                    String category = data[2];
//                    int price = Integer.parseInt(data[3]);
//
//                Product product = new Product(id, name, category, price);
//                service.addProduct(product);
//
//                    System.out.println(data[0]);
//                    System.out.println(data[1]);
//                    System.out.println(data[2]);
//                    System.out.println(data[3]);
//
//                for(int i = 0; i<data.length; i++){
//                    System.out.println(data[i]);
//                }
//
//                for(String str : data){
//                    System.out.println(str);
//                }
//                line = br.readLine();
//            }
//
//
//
//        }catch(FileNotFoundException file_Obj){
//            System.out.println("FileNotFoundException - Error");
//        }catch(IOException io_Obj){
//            System.out.println("IOException - Error");
//        }
//
//
//        Product p1 = new Product(101, "Laptop", "Electronics", 50000);
//        Product p2 = new Product(102, "Mobile", "Electronics", 30000);
//        Product p3 = new Product(102, "Chair", "Furniture", 5000);
//        service.addProduct(p2);
//
//        service.viewProduct();
//
//        service.searchProduct(102);
//
//        service.updateProduct(p3);
//
//        service.viewProduct();
//
//        service.deleteProduct(101);
//
//        service.viewProduct();
//
    }
}

DBConnection.java

package com.company.db;

import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.SQLException;

public class DBConnection{

    public static Connection getPSQLConnection(){
        Connection con = null;
        try{
            con = DriverManager.getConnection("jdbc:postgresql://localhost:5432/productdb", "postgres", "saravanan");
            System.out.println("SQL is connected");
        }
        catch(SQLException obj){
            System.out.println("SQL not connected");
        }
    return con;
    }


//public static void main(String[] args){
//    DBConnection.getPSQLConnection();
//}

}

Output:

SQL is connected
[3 , Laptop , Electronics , 50000, 2 , Ipad , Electronics , 40000]
SQL is connected
0
Product is Not Found
SQL is connected
[3 , Laptop , Electronics , 50000, 2 , Ipad , Electronics , 40000, 3 , Laptop , Electronics , 50000, 2 , Ipad , Electronics , 40000]
SQL is connected
[3 , Laptop , Electronics , 50000, 2 , Ipad , Electronics , 40000, 3 , Laptop , Electronics , 50000, 2 , Ipad , Electronics , 40000, 3 , Laptop , Electronics , 50000, 2 , Ipad , Electronics , 40000]
SQL is connected
1
Product is Updated
SQL is connected
[3 , Laptop , Electronics , 50000, 2 , Ipad , Electronics , 40000, 3 , Laptop , Electronics , 50000, 2 , Ipad , Electronics , 40000, 3 , Laptop , Electronics , 50000, 2 , Ipad , Electronics , 40000, 3 , Laptop , Electronics , 50000, 2 , Ipad , Electronics , 40000]
SQL is connected
3
Laptop
Electronics
50000

Java Learning Series - DB connection with Product Management System

Saravanan Lakshmanan — Thu, 17 Sep 2026 19:40:00 +0000

Today, I created DBConnection class to connect database with Java application.

DBConnection.java

package com.company.db;

import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.SQLException;

public class DBConnection{

    public static Connection getPSQLConnection(){
        Connection con = null;
        try{
            con = DriverManager.getConnection("jdbc:postgresql://localhost:5432/productdb", "postgres", "saravanan");
            System.out.println("SQL is connected");
        }
        catch(SQLException obj){
            System.out.println("SQL not connected");
        }
    return con;
    }
}

viewProduct() inside ProductService.java

    public void viewProduct() {
            try{
                Connection con = DBConnection.getPSQLConnection();
                String sql = "select * from products";
                PreparedStatement ps = con.prepareStatement(sql);
                System.out.println(ps);
                ResultSet rs = ps.executeQuery();
                System.out.println(rs);
                while(rs.next()){
                    System.out.println(rs.getInt("id"));
                    System.out.println(rs.getString("name"));
                    System.out.println(rs.getString("category"));
                    System.out.println(rs.getInt("price"));    
                }

            }catch(SQLException exe){
                System.out.println("SQLException");
            }
    }

Then, it has been called from Main.java

package com.company.controller;
import com.company.entity.Product;
import com.company.service.ProductService;

import java.io.File;
import java.io.FileReader;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.FileNotFoundException;

public class Main{

    public static void main(String[] args) {

        ProductService service = new ProductService();

        service.viewProduct();
  }
}

Output:

SQL is connected
select * from products
org.postgresql.jdbc.PgResultSet@43195e57
1
chair
furniture
10000
2
mobile
electronics
20000

Java Learning Series - Updated Product Management System

Saravanan Lakshmanan — Thu, 10 Sep 2026 18:31:18 +0000

Today, I learnt how to import a file using File class object instead of creating multiple objects.

Products.java

public class Product{

    private int id;
    private String name;
    private String category;
    private int price;

    public Product(int i, String n, String c, int p) {
        this.id = i;
        this.name = n;
        this.category = c;
        this.price = p;
    }

    public int getId() {
        return this.id;
    }

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

    public String getName() {
        return this.name;
    }

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

    public String getCategory() {
        return this.category;
    }

    public void setCategory(String category) {
        this.category = category;
    }

    public int getPrice() {
        return this.price;
    }

    public void setPrice(int price) {
        this.price = price;
    }

    public String toString() {
        return this.getId() + " , " + this.getName() + " , " + this.getCategory() + " , " + this.getPrice();
    }
}

ProductService.java

import java.util.ArrayList;

public class ProductService{

    ArrayList<Product> arr = new ArrayList();

    public void addProduct(Product product) {
        boolean addStatus = arr.add(product);
        if (addStatus) {
            System.out.println("Product is Added");
        } else {
            System.out.println("Product is not Added");
        }
    }

    public void viewProduct() {
        for (Product product : arr) {
            System.out.println(product);
        }
    }

    public void searchProduct(int id) {
        System.out.println();
        boolean found = false;

        for (Product product : arr) {
            if (product.getId() == id) {
                System.out.println(product.getId() + " - " + product.getName() + " - " + product.getCategory() + " - " + product.getPrice());
                found = true;
                break;
            }
        }

        if (found == true) {
            System.out.println("Product is Found");
        } else {
            System.out.println("Product is not Found");
        }
    }

    public void updateProduct(Product newProduct) {
        for (Product existingProduct : arr) {
            if (existingProduct.getId() == newProduct.getId()) {
                existingProduct.setName(newProduct.getName());
                existingProduct.setCategory(newProduct.getCategory());
                existingProduct.setPrice(newProduct.getPrice());
            }
        }
    }

    public void deleteProduct(int id) {
        boolean deleteStatus = false;

        for (Product product : arr) {
            if (product.getId() == id) {
                arr.remove(product);
                deleteStatus = true;
                break;
            }
        }

        if (deleteStatus == true) {
            System.out.println("Product is Deleted");
        } else {
            System.out.println("Product is Not Found");
        }
    }
}

Main.java

import java.io.File;
import java.io.FileReader;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.FileNotFoundException;

public class Main{

    public static void main(String[] args) {

        ProductService service = new ProductService();

        File file = new File("products.csv");
//        System.out.println(file.canRead());

        try{
            FileReader reader = new FileReader(file);
            BufferedReader br = new BufferedReader(reader);
            String line = br.readLine();

            line = br.readLine();
            while(line!=null){
                String[] data = line.split(",");
//                System.out.println(data);
//                System.out.println(line);

                    int id = Integer.parseInt(data[0]);
                    String name = data[1];
                    String category = data[2];
                    int price = Integer.parseInt(data[3]);

                Product product = new Product(id, name, category, price);
                service.addProduct(product);

//                    System.out.println(data[0]);
//                    System.out.println(data[1]);
//                    System.out.println(data[2]);
//                    System.out.println(data[3]);

//                for(int i = 0; i<data.length; i++){
//                    System.out.println(data[i]);
//                }

//                for(String str : data){
//                    System.out.println(str);
//                }
                line = br.readLine();
            }



        }catch(FileNotFoundException file_Obj){
            System.out.println("FileNotFoundException - Error");
        }catch(IOException io_Obj){
            System.out.println("IOException - Error");
        }


//        Product p1 = new Product(101, "Laptop", "Electronics", 50000);
//        Product p2 = new Product(102, "Mobile", "Electronics", 30000);
//        Product p3 = new Product(102, "Chair", "Furniture", 5000);
//        service.addProduct(p2);
//
        service.viewProduct();
//
        service.searchProduct(102);

//        service.updateProduct(p3);

        service.viewProduct();

        service.deleteProduct(101);

        service.viewProduct();
//
    }
}

Output:

Product is Added
Product is Added
Product is Added
101 , Laptop , Electronics , 50000
102 , Mobile , Electronics , 20000
103 , Chair , Furniture , 10000

102 - Mobile - Electronics - 20000
Product is Found
101 , Laptop , Electronics , 50000
102 , Mobile , Electronics , 20000
103 , Chair , Furniture , 10000
Product is Deleted
102 , Mobile , Electronics , 20000
103 , Chair , Furniture , 10000

Java Learning Series - Exploring Java File Class: Listing Files and Folders

Saravanan Lakshmanan — Wed, 09 Sep 2026 18:47:17 +0000

Today, I explored Java File class and created the mini task using it's methods.

import java.io.File;
import java.io.IOException;

public class FileList {

    public static void main(String[] args){
        File file = new File("/home/saravanan/FullStack/front-end/Back-end/Java");
        File[] files = file.listFiles();
            System.out.println();
            System.out.println(files); //tried to print the entire Objects in an Array
            System.out.println();
            System.out.println("List of Files: ");
            System.out.println();

        for(File obj : files){
            boolean fileStatus = obj.isFile();
//          boolean folderStatus = obj.isDirectory();
            if(fileStatus){
                System.out.println("File Name: " + obj.getName());
                System.out.println("Path : " + obj.getPath());
                System.out.println("Absolute Path : " + obj.getAbsolutePath());
                try{
                System.out.println("Canonical Path : " + obj.getCanonicalPath());
                }catch(IOException io){
                    System.out.println("Canonical Path Error");
                }
                System.out.println("File Length: " + obj.length());
                System.out.println();
            }

//            if(folderStatus){
//                System.out.println(obj.getName());
//            }

        }
            System.out.println();
            System.out.println("List of Folders: ");
            System.out.println();

        for(int i = 0; i<files.length; i++){
            boolean folderStatus = files[i].isDirectory();
        if(folderStatus){
            System.out.println("Folder Name: " + files[i].getName());
            System.out.println("Path : " + files[i].getPath());
            System.out.println("Absolute Path : " + files[i].getAbsolutePath());
            try{
                System.out.println("Canonical Path: " + files[i].getCanonicalPath());
                }catch(IOException io){
                    System.out.println("Canonical Path Error");
                }
            System.out.println("Folder Length: " + files[i].length());
            System.out.println();
        }
        }
    }

}

Output:

[Ljava.io.File;@2a139a55

List of Files: 

File Name: Customers.class
Path : /home/saravanan/FullStack/front-end/Back-end/Java/Customers.class
Absolute Path : /home/saravanan/FullStack/front-end/Back-end/Java/Customers.class
Canonical Path : /home/saravanan/FullStack/front-end/Back-end/Java/Customers.class
File Length: 530

File Name: Student.class
Path : /home/saravanan/FullStack/front-end/Back-end/Java/Student.class
Absolute Path : /home/saravanan/FullStack/front-end/Back-end/Java/Student.class
Canonical Path : /home/saravanan/FullStack/front-end/Back-end/Java/Student.class
File Length: 902

File Name: FileList.java
Path : /home/saravanan/FullStack/front-end/Back-end/Java/FileList.java
Absolute Path : /home/saravanan/FullStack/front-end/Back-end/Java/FileList.java
Canonical Path : /home/saravanan/FullStack/front-end/Back-end/Java/FileList.java
File Length: 2150

File Name: Student.java
Path : /home/saravanan/FullStack/front-end/Back-end/Java/Student.java
Absolute Path : /home/saravanan/FullStack/front-end/Back-end/Java/Student.java
Canonical Path : /home/saravanan/FullStack/front-end/Back-end/Java/Student.java
File Length: 1094

File Name: SuperMarket.java
Path : /home/saravanan/FullStack/front-end/Back-end/Java/SuperMarket.java
Absolute Path : /home/saravanan/FullStack/front-end/Back-end/Java/SuperMarket.java
Canonical Path : /home/saravanan/FullStack/front-end/Back-end/Java/SuperMarket.java
File Length: 1210

File Name: Customers.java
Path : /home/saravanan/FullStack/front-end/Back-end/Java/Customers.java
Absolute Path : /home/saravanan/FullStack/front-end/Back-end/Java/Customers.java
Canonical Path : /home/saravanan/FullStack/front-end/Back-end/Java/Customers.java
File Length: 377

File Name: Grt.java
Path : /home/saravanan/FullStack/front-end/Back-end/Java/Grt.java
Absolute Path : /home/saravanan/FullStack/front-end/Back-end/Java/Grt.java
Canonical Path : /home/saravanan/FullStack/front-end/Back-end/Java/Grt.java
File Length: 504

File Name: StudentService.java
Path : /home/saravanan/FullStack/front-end/Back-end/Java/StudentService.java
Absolute Path : /home/saravanan/FullStack/front-end/Back-end/Java/StudentService.java
Canonical Path : /home/saravanan/FullStack/front-end/Back-end/Java/StudentService.java
File Length: 1497


List of Folders: 

Folder Name: Pro1
Path : /home/saravanan/FullStack/front-end/Back-end/Java/Pro1
Absolute Path : /home/saravanan/FullStack/front-end/Back-end/Java/Pro1
Canonical Path: /home/saravanan/FullStack/front-end/Back-end/Java/Pro1
Folder Length: 4096

Folder Name: Pro2
Path : /home/saravanan/FullStack/front-end/Back-end/Java/Pro2
Absolute Path : /home/saravanan/FullStack/front-end/Back-end/Java/Pro2
Canonical Path: /home/saravanan/FullStack/front-end/Back-end/Java/Pro2
Folder Length: 4096

Folder Name: Inheritance-Method_Overriding
Path : /home/saravanan/FullStack/front-end/Back-end/Java/Inheritance-Method_Overriding
Absolute Path : /home/saravanan/FullStack/front-end/Back-end/Java/Inheritance-Method_Overriding
Canonical Path: /home/saravanan/FullStack/front-end/Back-end/Java/Inheritance-Method_Overriding
Folder Length: 4096

Folder Name: StudentManagementSystem
Path : /home/saravanan/FullStack/front-end/Back-end/Java/StudentManagementSystem
Absolute Path : /home/saravanan/FullStack/front-end/Back-end/Java/StudentManagementSystem
Canonical Path: /home/saravanan/FullStack/front-end/Back-end/Java/StudentManagementSystem
Folder Length: 4096

Folder Name: ProductManagementSystem
Path : /home/saravanan/FullStack/front-end/Back-end/Java/ProductManagementSystem
Absolute Path : /home/saravanan/FullStack/front-end/Back-end/Java/ProductManagementSystem
Canonical Path: /home/saravanan/FullStack/front-end/Back-end/Java/ProductManagementSystem
Folder Length: 4096

Java Learning Series - Product Management System

Saravanan Lakshmanan — Tue, 08 Sep 2026 18:40:43 +0000

Today, I created Product Management System in Java.

Product.java

public class Product{

    private int id;
    private String name;
    private String category;
    private int price;

    public Product(int i, String n, String c, int p) {
        this.id = i;
        this.name = n;
        this.category = c;
        this.price = p;
    }

    public int getId() {
        return this.id;
    }

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

    public String getName() {
        return this.name;
    }

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

    public String getCategory() {
        return this.category;
    }

    public void setCategory(String category) {
        this.category = category;
    }

    public int getPrice() {
        return this.price;
    }

    public void setPrice(int price) {
        this.price = price;
    }

    public String toString() {
        return this.getId() + " , " + this.getName() + " , " + this.getCategory() + " , " + this.getPrice();
    }
}

ProductService.java

import java.util.ArrayList;

public class ProductService{

    ArrayList<Product> arr = new ArrayList();

    public void addProduct(Product product) {
        boolean addStatus = arr.add(product);
        if (addStatus) {
            System.out.println("Product is Added");
        } else {
            System.out.println("Product is not Added");
        }
    }

    public void viewProduct() {
        for (Product product : arr) {
            System.out.println(product);
        }
    }

    public void searchProduct(int id) {
        System.out.println();
        boolean found = false;

        for (Product product : arr) {
            if (product.getId() == id) {
                System.out.println(product.getId() + " - " + product.getName() + " - " + product.getCategory() + " - " + product.getPrice());
                found = true;
                break;
            }
        }

        if (found == true) {
            System.out.println("Product is Found");
        } else {
            System.out.println("Product is not Found");
        }
    }

    public void updateProduct(Product newProduct) {
        for (Product existingProduct : arr) {
            if (existingProduct.getId() == newProduct.getId()) {
                existingProduct.setName(newProduct.getName());
                existingProduct.setCategory(newProduct.getCategory());
                existingProduct.setPrice(newProduct.getPrice());
            }
        }
    }

    public void deleteProduct(int id) {
        boolean deleteStatus = false;

        for (Product product : arr) {
            if (product.getId() == id) {
                arr.remove(product);
                deleteStatus = true;
                break;
            }
        }

        if (deleteStatus == true) {
            System.out.println("Product is Deleted");
        } else {
            System.out.println("Product is Not Found");
        }
    }
}

Main.java

public class Main{

    public static void main(String[] args) {

        Product p1 = new Product(101, "Laptop", "Electronics", 50000);
        Product p2 = new Product(102, "Mobile", "Electronics", 30000);
        Product p3 = new Product(102, "Chair", "Furniture", 5000);

        ProductService service = new ProductService();

        service.addProduct(p1);
        service.addProduct(p2);

        service.viewProduct();

        service.searchProduct(102);

        service.updateProduct(p3);

        service.viewProduct();

        service.deleteProduct(101);

        service.viewProduct();

    }
}

Output:

Product is Added
Product is Added
101 , Laptop , Electronics , 50000
102 , Mobile , Electronics , 30000

102 - Mobile - Electronics - 30000
Product is Found
101 , Laptop , Electronics , 50000
102 , Chair , Furniture , 5000
Product is Deleted
102 , Chair , Furniture , 5000

Java Learning Series - Inheritance & Method-Overriding

Saravanan Lakshmanan — Mon, 07 Sep 2026 15:47:00 +0000

Today, I learnt Inheritance & Method-Overriding and made a mini-task.

Inheritance - Child class can use Parent class method using keyword extends, instead of creating it again in Child class.

Method-Overriding - Instead of using the same implementation/logic of Parent class method, Child class can override it's own implementation but with same method name, same number of arguments, same type of arguments and same return type.

Parent.java

public class Parent{

    public void parent_method(){
        System.out.println("I'm Parent Method'");
    }

}

Child.java

public class Child extends Parent{

    public static void main(String[] args){

        Child c = new Child();

        c.parent_method(); //checked for Inheritance concept
        c.parent_method(); //called for Method-Overriding

    }

    @Override
    public void parent_method(){
        System.out.println("I'm new Child method now'");
    }


}

Main.java

public class Main{

    public static void main(String[] args){
        Child c = new Child();
        Parent p = new Parent();

        c.parent_method();
        p.parent_method();
    }

}

Output:

I'm new Child method now'
I'm Parent Method'

Python Learning Series - Python Pattern Task

Saravanan Lakshmanan — Fri, 04 Sep 2026 05:54:56 +0000

Task 1:

for row in range(1,6):
    for col in range(1,row+1):
        print(0 if (row+col) % 2 == 0 else 1, end = '\t')
    print()

Output:

0   
1   0   
0   1   0   
1   0   1   0   
0   1   0   1   0

Task 2:


for row in range(1,6):
    for col in range(1,row+1):
        print(1 if (col % 2) == 0 else 0, end = '\t')
    print()

Output:

0   
0   1   
0   1   0   
0   1   0   1   
0   1   0   1   0

Task 3:

for row in range(1,6):
    for col in range(1,row+1):
        print(1 if (row % 2) == 0 else 0, end = '\t')
    print()

Output:

0   
1   1   
0   0   0   
1   1   1   1   
0   0   0   0   0

Java Learning Series - Student Management System

Saravanan Lakshmanan — Wed, 02 Sep 2026 20:05:25 +0000

Today, I practiced and built a simple Student Management System using Java with separate classes for better code organization.

Add Student
View Students
Search Student
Delete Student
Modify Student

Practicing Java OOP, Classes, Objects, ArrayList, and Methods.

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 int getId(){
        return this.id;
    }

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

    public String getName(){
        return this.name;
}

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

    public String getCourse(){
        return this.course;
}

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

    public int getMark(){
        return this.mark;
}

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

}

StudentService.java

import java.util.ArrayList;

public class StudentService{

//add
//view
//delete
//search
//modify


    ArrayList<Student> arr = new ArrayList();

public void addStudent(Student student){
    arr.add(student);
}

public void viewStudent(){
        System.out.println();
        System.out.println("**********The Student List************************");
    for(Student student : arr){
        System.out.println("Student Id: " + student.getId());
        System.out.println("Student Name: " + student.getName());
        System.out.println("Student Course: " + student.getCourse());
        System.out.println("Student Mark: " + student.getMark());
        System.out.println();
}
        System.out.println("****************************************************");
        System.out.println();
}

public void updateStudent(int id, String name, String course, int mark){
    for(Student student : arr){
        if(student.getId() == id){
             System.out.println("**********Student Updated**************************");
             student.setName(name);
             student.setCourse(course);
             student.setMark(mark);
             System.out.println("****************************************************");
             System.out.println();
             return;

    }
    }
   System.out.println("Student Not Found");
}

public void searchStudent(int id){
        System.out.println();
        System.out.println("**********Search List************************");
    for(Student student : arr){
        if(student.getId() == id){
             System.out.println("Student Found");
             System.out.println("Student ID: " + student.getId());
             System.out.println("Student Name: " + student.getName());
             System.out.println("Student Course: " + student.getCourse());
             System.out.println("Student Mark: " + student.getMark());
             System.out.println();
             return;
}
} 
   System.out.println("Student Not Found");
}

public void deleteStudent(int id){
        System.out.println();
        System.out.println("*********************************************");
    for(Student student : arr){
        if(student.getId() == id){
            arr.remove(student);
            System.out.println("Student Deleted");
            return;
    }
}
   System.out.println("Student Not Found");
}

}

Main.java

public class Main{

    public static void main(String[] args){

        Student s1 = new Student(101,"Saravanan", "Java", 100);  
        Student s2 = new Student(102,"Saran", "JS", 99);        
        Student s3 = new Student(103,"Dhana", "Python", 89);

        StudentService service = new StudentService();

        service.addStudent(s1);
        service.addStudent(s2);
        service.addStudent(s3);

        service.viewStudent();


        service.updateStudent(102, "Ravi", "C#", 77);
        service.viewStudent();

        service.searchStudent(103);

        service.deleteStudent(101);
        service.viewStudent();
    }

}

Output:

**********The Student List************************
Student Id: 101
Student Name: Saravanan
Student Course: Java
Student Mark: 100

Student Id: 102
Student Name: Saran
Student Course: JS
Student Mark: 99

Student Id: 103
Student Name: Dhana
Student Course: Python
Student Mark: 89

****************************************************

**********Student Updated**************************
****************************************************


**********The Student List************************
Student Id: 101
Student Name: Saravanan
Student Course: Java
Student Mark: 100

Student Id: 102
Student Name: Ravi
Student Course: C#
Student Mark: 77

Student Id: 103
Student Name: Dhana
Student Course: Python
Student Mark: 89

****************************************************


**********Search List************************
Student Found
Student ID: 103
Student Name: Dhana
Student Course: Python
Student Mark: 89


*********************************************
Student Deleted

**********The Student List************************
Student Id: 102
Student Name: Ravi
Student Course: C#
Student Mark: 77

Student Id: 103
Student Name: Dhana
Student Course: Python
Student Mark: 89

****************************************************

Python Learning Series - Pattern programs

Saravanan Lakshmanan — Wed, 02 Sep 2026 10:39:34 +0000

Task 1

no = 0
for row in range(6,1,-1):
    for col in range(1,row):  
        no+=1 
        print(no, end = ' ')
    print()

Output:

Task 2

for row in range(6,1,-1):
    for col in range(1,row):
        print(chr(64+col), end = '  ')
    print()

Output:

A B C D E
A B C D
A B C
A B
A

Java Learning Series - Creating POJO class

Saravanan Lakshmanan — Mon, 31 Aug 2026 14:29:41 +0000

Today, I've created POJO (Plain Old Java Object) class for Student Management System and practiced using constructor, getter, setter and encapsulation.

public class Student{
        //creating private non-static global variable
        private int id;
        private String name;
        private String course;
        private int mark;

    //creating constructors with 4 parameters
    public Students(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,"Saravanan", "BCA", 500);
            s1.getId();

}
    //creating getter & setter methods for id
    public int getId(){
        return this.id;
}
    public void setId(int id){
        this.id = id;
}

    //creating getter & setter methods for name
    public String getName(){
        return this.name;
}
    public void setName(String name){
        this.name = name;
}

    //creating getter & setter methods for course
    public String getCourse(){
        return this.course;
}
    public void setCourse(String course){
        this.course = course;
}

    //creating getter & setter methods for mark
    public int getMark(){
        return this.mark;
}
    public void setMark(int mark){
        this.mark = mark;
}


}