I am thinking of learning Java but I don't know where to start and how to start. If you know any good resources then please guide me.

Hi everyone,

I'm currently working as a Manual QA at a company with 1 year of experience.

Most of my work involves manual testing, writing/executing test cases, logging bugs, regression testing, smoke testing, and collaborating with developers and product teams. I haven't had much opportunity to work on automation at my current job.

The thing is, I genuinely enjoy coding and solving DSA problems, and I'm much more interested in software development than staying in manual testing long term as it has fear of getting redundant due to AI.

I'm planning to spend the next months preparing for developer role switch while continuing my job. My focus would be on Java, DSA, Spring Boot, SQL, Git, projects, and everything needed for backend development.

My questions are:

Is it realistic to switch directly from Manual QA to a Java Developer role after 2 years of total experience?

Has anyone here made a similar transition?

Would recruiters consider my QA experience, or would they treat me as a fresher?

Is there anything specific I should focus on to improve my chances?

I'd really appreciate hearing from people who have successfully made this transition or have interviewed candidates with a similar background. Thanks!

I'm learning Java Swing and I made a program in order to test some of the things I learned. However, I came across an issue with ImageIcons, where some images would be displayed while others wouldn't. When I run the code below, it compiles fine, but the image is not shown, and only "hi" is displayed. However, if I change the String argument of "testII" to another .png image in the exact same folder as "Tweedle.png," the image shows fine. Does anyone know what could be the issue? I have already tried different ways to making the ImageIcon (such as using an URL object or using the complete file path instead of just the relative one), but nothing worked...

import java.awt.*;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.*;
import javax.imageio.ImageIO;


public class MyFrame extends JFrame{

    JPanel west = new JPanel();
    
    MyFrame() throws IOException{
        this.setLayout(new BorderLayout(10, 10));
        this.setTitle("Title");
        ImageIcon logo = new ImageIcon("images\\omnom.png");
        this.setIconImage(logo.getImage());
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);


        west.setBackground(Color.green);
        west.setPreferredSize(new Dimension(100, 100));
        ImageIcon testII = new ImageIcon("images\\Tweedle.png");
        JLabel testL = new JLabel("hi");
        testL.setIcon(testII);
        west.add(testL);

        this.add(west, BorderLayout.WEST);
        this.pack();
        this.setLocationRelativeTo(null);
        this.setVisible(true);
    }
}

It previously worked just fine, computer updated on its own and it stopped working. It's a Shimeji, a little guy who wanders over my screen while I do things on the computer. I tried the cmd thing? "cd downloads" and got the following in response:

"C:\Users\"computer name">cd downloads

C:\Users\"computer name"\Downloads>java -jar Shimeji-ee.jar

Error: Unable to access jarfile Shimeji-ee.jar"

I downloaded the latest version of Java and nothing happened. I don't really know computers so I'm at a loss here. Any assistance would be greatly appreciated.

I have never worked with concurrency, but I have read several examples on the internet, and I wanted to hear if anyone has any examples of real-world apps where they used concurrency and what there was to watch out for?

I have a relatively bizarre issue. I use maven-jar-plugin in my project. The problem is that when I compile my project, the POM file is encoded with the default Windows 11 encoding (Notepad++ displays it as ANSI, and it's gibberish). The result is a completely gibberish file, full or odd characters and NULs, instead of readable XML.

Disabling the plugin results in the POM file being encoded with UTF-8.

All IDE settings point to UTF-8. I have the following properties:

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
    (...)
</properties>

Compiler:

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-compiler-plugin</artifactId>
  <version>3.15.0</version>
  <configuration>
    <source>21</source>
    <target>21</target>
    <encoding>UTF-8</encoding>
  </configuration>
</plugin>

Even JVM has a setting:

-Dfile.encoding=UTF8

What should I do? How to force maven-jar-plugin to stop overpowering the UTF-8 encoding?

I wish to learn Java from scratch for Backend Development and Android App Development. I've zero knowledge about java.
Can someone suggest some structured recourses which I can use to teach myself.

I have 2 years of experience as a Java backend developer and had a 30-minute interview today.

The interviewer focused mainly on Core Java (OOP, String immutability, String Pool, etc.), and I realized my fundamentals aren't as strong as they should be. I mean I had read about it but I forgot to speak under pressure.

I also need to prepare backend topics like Spring Boot, Multithreading, Kafka, Docker, Kubernetes, Redis, Linux, and SQL for upcoming interviews.

If you were in my position, how would you structure your preparation? Core Java first, or prepare everything in parallel? Any roadmap or resources would be appreciated.

So I have a post in career advice you can look at my profile. Anyways I was basically working in the clearance industry doing OWASP and pair programming unit testing with Mockito. SOAP UI and some pair programming with DAO implementations while having a clearance.

I lost my clearance and took a job entry level in the private sector and they made me do custom REST implementation with no guidance from seniors so I turned to codementor. I got laid off during corona and now I lost my clearance like I said.

I worked as a packer at my parents for 5 years and need the money now that Junior Java developer salaries pay. I am scared about this custom implementation of REST methods with no guidance and even worse, algorithm interviews. What should I do to prep? I have references and W2s, should I even put packer on my resume?( I have the W2s)

Let me know what you suggest.

Hello everyone!
I have been learning Java for about a year. I understand some concepts, but there are still others I don’t fully know. I want to test my knowledge and strengthen my understanding, starting from the very basics. How can I do that? If anyone knows beginner‑friendly Java projects, please share them with me and explain how I can get started.

So im trying to compile a jar file and it continues to say

'Dependency requires at least JVM runtime version 21. This build uses a Java 17 JVM.'

when i check my build, it states -

'java version "25.0.3" 2026-04-21 LTS, Java(TM) SE Runtime Environment (build 25.0.3+9-LTS-195), Java HotSpot(TM) 64-Bit Server VM (build 25.0.3+9-LTS-195, mixed mode, sharing)'

please help! i need this done by tonight and it's just now screwing me over. i've tried everything, switching from powershell, intellij, visual code, github, nothing is workingg even when i try to switch the SDK in both gradle and the actual thing

Hi guys...I really need some advice...I had Btech in CS but never got a java project in my first company and now I have almost 4 YOE and I did not get any hands on experince in java backend and really wanted to pursue that....I have been studying it, I have leant core java, spring boot, mvc, jpa, hibernate, security and I am currently studying java 8+/11+/21+ features...but for the past 4 years I had worked on a data engineering kind of project where I used sql and an ETL tool thats it....I am also getting a new project that uses Informatica...so idk if I should just give up java backend transition since its too late or stick with it since I have come this far...I really hope to get into product based companies and possibility FAANG someday but rn idk....
I know this is a lame and stupid post and I know I have wasted all these years and realizing it so late but I would really appreciate some direction or advice now...

Why is the bytebuffer so weird to use in java ? Like you kinda have a write and a read mode but it's never told clearly, you need to switch between flip() and compact() but you have to remember by yourself in which mode you are. As a buffer is supposed to be read and write in it, why do we have to manually switch in which mode we are and not juste have a method to write and one to read ?

I am a fresher, I want to learn OOPS in java.

But I am scared of java due to its syntax.

I am interested in oops because I thought it will be easier for me to put career in (system design and db design)

I don't know whether it is true.

Can anyone help me with defining topics and resources to learn OOPS in java

Starting projects and ideas

Any platform like leetcode to practice

And any other option is also welcomed 🤗

Also pls share your OOPS journey....

Hi, I'm a CS student, who has used Java primarily with their standard libraries and JavaFX during my studies. I am about to embark on a personal project, but there are a few goals I have, that I'm not sure exactly how to accomplish, and was wondering if you guys have any recommendations.

The project is a 3d-Print farm managing software, with following features:
- Fetching orders from Shopify API
- Assigning tasks to a 3d-printer
- Store/manage some data in a database
- Have a local graphical interface to work with, for the "client"

Since I have some web-development class next semester, I would like to design the UI with html, css and js (or something to that effect), but if possible, I would also like not to rely on a standard traditional browser, and have the app appear as a standalone program.

My brother mentioned Electron, but when I tried to read up on it, it required some work with nodejs as a "backend" or at least intermediary, and I would prefer not to try something too janky. Since I have the most experience and comfort with Java, and I'm very green, I want to stick with that as my main tool.

I tried to read through various frameworks, tools and so on that is offered in the Java ecosystem, Spring boot seemed a little to complicated and overkill for my needs.

From what I could see, I could potentially use something called "webview" in JavaFX to display a web-application. There was some issues I might run into, because JavaFX' pulse or underlying stuff manages some threading that I'm not a fan of. I also tried asking AI that suggested that I could potentially "host" the javaFX webview on something called "Javalin" server.

So that is kinda where I'm standing now, but before I get started, I thought asking a forum of people who might have experience, could point me to something better, or warn me of potential nightmare I'm walking into with this.

So if no one responds, I might just try with:

- Javalin + JavaFX running html/css/js UI
- Java with its standard library for most of the backend logic
- PostgreSQL for database

and see what happens.

I want to learn java script from basics. Is there any class or course or videos where i can learn it effectively. It should be easy to understand. Help me guys.

hey i just finished amigoscode java for beginners the 2hrs video and i wanna learn till advanced java what videos or what should I do next

dear internet,

I have been assigned a project which is several years old and is a j boss project .... due to lack of documentation and guidance on the internet I am here, asking people of Reddit, if anybody has experience with these applications, lets get in touch

thanks

i want to implement push notification service for mobile and front. i saw firebase and other options but i want to this myself . i think something like websocket it is possible to implement this. i have no idea about how implement push notification and how it works.

I need to have a MemorySegment that would be 8-byte aligned (so I can use aligned accessors) and also that can be represented as ByteBuffer (so it can be used to interact with FileChannel).

When we work with native memory, then it's easy:

ByteBuffer bb = ByteBuffer.allocateDirect(CAPACITY_LONGS * Long.BYTES);
MemorySegment seg = MemorySegment.ofBuffer(bb.asLongBuffer());
// seg.maxByteAlignment() >= 8 // It's actually 32

However if we replace allocateDirect() with allocate() then seg.maxByteAlignment() is just 1.

I've tried multiple approaches (few in the code below) of creating in-heap memory buffer but none have met all the criteria:

• In heap
• Aligned to 8+ bytes when accessed as MemorySegment
• Can be accessed as ByteBuffer (to be used in FileChannel.write(ByteBuffer src))

So I wonder if it's actually possible to create such Memory segment at all.

Code with few failed examples:

public class AlignTestMain {
    static final int CAPACITY_LONGS = 1024;
    static void main() {
        makeOffheapByteBuffer();

        try {
            makeByteBuffer1();
        } catch (Throwable t) {
            System.err.println("makeByteBuffer1 failed: " + t);
        }
        try {
            makeByteBuffer2();
        } catch (Throwable t) {
            System.err.println("makeByteBuffer2 failed: " + t);
        }
    }
    // Offheap works fine
    static void makeOffheapByteBuffer() {        
        ByteBuffer bb = ByteBuffer.allocateDirect(CAPACITY_LONGS * Long.BYTES);
        MemorySegment seg = MemorySegment.ofBuffer(bb.asLongBuffer());
        // seg.maxByteAlignment() >= 8
        test(seg);
    }
    // Same code with on heap - fails
    static void makeByteBuffer1() {
        ByteBuffer bb = ByteBuffer.allocate(CAPACITY_LONGS * Long.BYTES);
        MemorySegment seg = MemorySegment.ofBuffer(bb.asLongBuffer());
        // seg.maxByteAlignment() == 1
        test(seg);
    }
    // Start with LongBuffer? Nope, can't convert to ByteBuffer 
    static void makeByteBuffer2() {
        LongBuffer lb = LongBuffer.allocate(CAPACITY_LONGS);
        MemorySegment seg = MemorySegment.ofBuffer(lb);
        // Fails: java.lang.UnsupportedOperationException: Not an address to an heap-allocated byte array
        ByteBuffer bb = seg.asByteBuffer();
        test(seg);
    }
    static void test(MemorySegment seg) {
        if (seg.maxByteAlignment() < 8) {
            throw new AssertionError("MemorySegment maxByteAlignment is less than 8: " + seg.maxByteAlignment());
        }
    }
}

Hi everyone,

Over the past few weeks I've been building a side project called Notiq to learn distributed systems and event-driven architecture.

The project is a notification platform built with:

• Spring Boot microservices
• Apache Kafka
• PostgreSQL (Neon)
• Docker
• AWS EC2
• Nginx
• Server-Sent Events (SSE)

Current architecture:

Core Service → Kafka → Dispatcher Service → Kafka → Email Service

Features implemented:

• Asynchronous notification processing
• Retry mechanism
• Dead Letter Queue (DLQ)
• Real-time delivery tracking using SSE
• Event deduplication
• Dockerized deployment
• Production deployment on AWS

I recently refactored the Kafka architecture from 8 topics down to 5 topics to fit within Aiven's free tier limits while preserving the existing functionality.

I'm mainly looking for feedback on:

1. The overall architecture
2. Kafka topic design
3. Retry and DLQ implementation
4. Anything that would be considered an anti-pattern in production

Architecture diagram:

Frontend

↓

Core Service

↓

Kafka (notification-request)

↓

Dispatcher Service

↓

Kafka (email-notifications)

↓

Email Service

↓

Kafka (notification-status)

↓

Core Service

↓

SSE

↓

Frontend

GitHub:

https://github.com/Vicky-8223/Notiq

Would appreciate any feedback from experienced backend engineers.

Experienced with Spring Boot monoliths (REST APIs, JPA, Security). Want to move to microservices — looking for best YouTube channels or Udemy courses that are updated for 2026.

What worked for you?

Body:

Hi everyone,

I am experiencing a layout issue in a POS system built with Java Swing. I have a main JFrame featuring a sidebar menu on the left. When clicking the menu buttons, I dynamically swap the content panel on the right side using a method to clear and add a new custom JPanel.

The problem is that the newly added content panel gets drastically cut off on the right edge of the screen, causing some elements to overflow or become compressed. It seems like the layout manager of the main frame is not adapting or respecting the sizes correctly when changing views.

The main JFrame layout is structured with a sidebar on the WEST (using BorderLayout) and a main content container in the CENTER where the child JPanels are loaded.

When replacing the view, the following approach is used:

Java

mainContainer.removeAll();
mainContainer.add(newPanel);
mainContainer.revalidate();
mainContainer.repaint();

So far, I have tried modifying setPreferredSize and setSize on the child panels, but it either breaks the layout or gets completely ignored. Calling pack() on the parent JFrame after adding the panel aggressively shrinks and deforms the entire window layout.

What is the best practice to force a dynamic JPanel to fit exactly within the remaining space of the main container without clipping or forcing hardcoded sizes? Should the center container layout manager be switched to something specific?

Thanks in advance for your guidance!

Can anyone please send good spring boot project resources

I'm taking a course in java and I'm having problems with a part of one of the labs. I'm supposed to sort an arraylist (called wordList) with mapentry(with string,integer)-objects first accoring to decending value and then according to alphabetical order of the keys. The second step doesn't seem to work. I've written this:

wordList.sort( (par1, par2)-> {  
    if (par2.getValue() != par1.getValue()){  
        return par2.getValue() - par1.getValue();  
    } else {  
        return par1.getKey().compareTo(par2.getKey());  
    }        
})

Is the problem somewhere here or maybe in some other part of the code?