Day-7 - Java Interview Questions & URL Shortener

Introduction

In Day 7, I learned Java Interview Questions Like Difference Between Final, Finally and Finalize and Method Overloading vs Method Overriding and Comparable vs Comparator and Also Implement URL Shortener. The Session Is Live in Youtube Channel By Navin Reddy Sir.

Java Interview Questions

Final, Finally And Finalize

Final : Final variable can't change value, final method cannot override and Final class cannot be extended.

Finally: Finally is Block in java, finally block is always executed it is use to close connection when we use database connectivity.

Finalize: Finalize is a method call by garbage collector. It is used to release all the resources used by the object  .

Method Overloading And Method Overriding

Method Overloading: In a Same Class We have Methods With Same Name And Same Parameters. Method Overloading allows different methods to have the same name, but different signatures where the signature can differ by the number of input parameters or type of input parameters, or a mixture of both. 

Method Overriding: If subclass (child class) has the same method as declared in the parent class, it is known as method overriding in Java.

Comparator and Comparator

URL Shortener

Complete Code Link: Link

package com.urlshort.urlshortspringproject;


import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;


import java.util.HashMap;
import java.util.Map;
import java.util.Random;



@Controller
public class URLShortController {
    private Map<String, String> urlMap = new HashMap<>();
    private Random random = new Random();


    @PostMapping("/generate")
    @ResponseBody
    public String generateShortURL(@RequestParam("longURL") String longURL) {
        // Check if the original URL is already present in the map
        for (Map.Entry<String, String> entry : urlMap.entrySet()) {
            if (entry.getValue().equals(longURL)) {
                return entry.getKey();
            }
        }


        // Generate a new short URL
        String shortURL = generateShortURLFromOriginalURL(longURL);
        urlMap.put(shortURL, longURL);
        return shortURL;
    }


    private String generateShortURLFromOriginalURL(String longURL) {
        String characters = extractCharacters(longURL);
        int length = 6;
        StringBuilder sb = new StringBuilder();


        for (int i = 0; i < length; i++) {
            int randomIndex = random.nextInt(characters.length());
            char randomChar = characters.charAt(randomIndex);
            sb.append(randomChar);
        }


        return "telus.ko/" + sb.toString();
    }


    private String extractCharacters(String longURL) {
        // Remove "https://" from the beginning of the URL
        String withoutHttps = longURL.replaceFirst("^https://", "");


        // Remove "www" from the beginning of the URL if it exists
        String withoutWWW = withoutHttps.replaceFirst("^www.", "");


        // Remove any remaining special characters
        String characters = withoutWWW.replaceAll("[^a-zA-Z0-9]", "");


        if (characters.isEmpty()) {
            throw new IllegalArgumentException("Invalid URL");
        }


        return characters;
    }
}        

1. The URLShortController class is a Spring MVC controller.
2. It handles POST requests to the /generate endpoint.
3. It accepts the long URL as a request parameter using @RequestParam.
4. It maintains a urlMap to store the mapping between original URLs and short URLs.
5. When a long URL is provided, it checks if it already exists in the urlMap.
6. If found, it returns the corresponding short URL from the map.
7. If not found, it generates a new short URL based on the provided long URL.
8. The short URL is generated by extracting characters from the long URL and creating a random 6-character string.
9. The generated short URL is prefixed with "telus.ko/".
10. The short URL is added to the urlMap for future reference.
11. The generated short URL is returned as the response.

There is a index.html in resource->template folder which is handle front end.

Thanks To Navin Reddy Sir To learn me this new concepts. In this article I tried my best to explain. Thanks!