Java

Java for people starting out: classes, collections, exceptions and the object-oriented ideas the language is built around.

21 guides

Java

Introduction to Java

What Java is, how the JVM works, where it is used, and your first program — plus an honest comparison with Python,…

Nov 12, 2026 5 min read

Java

Java Testing

Unit tests with JUnit 5: assertions, parameterised tests, mocking with Mockito, Spring Boot slice tests, and what is actually worth testing.

Nov 10, 2026 5 min read

Java

Spring Boot Whitelabel Error Page: What It Means and How to Fix It

The Whitelabel page is Spring Boot's default error screen. What the status and message on it are telling you, the four usual…

Nov 9, 2026 5 min read

Java

Fixing “Error creating bean with name” in Spring Boot

The first Spring error everyone meets. It wraps the real cause several layers down. How to find it, and the six causes:…

Nov 8, 2026 4 min read

Java

Java and the Spring Framework

What Spring actually does: dependency injection, beans and configuration, plus Spring Boot, and how a request travels through a Spring application.

Nov 7, 2026 5 min read

Java

java.lang.NullPointerException Explained and Fixed

Something was null when you used it. Modern Java tells you exactly what. How to read the helpful message, the five usual…

Nov 7, 2026 4 min read

Java

Fixing “error: cannot find symbol” in Java

The compiler cannot find a name you used. The message tells you the symbol and where. A typo, a missing import, wrong…

Nov 6, 2026 4 min read

Java

Java GUI Programming

Building desktop interfaces in Java: Swing for simplicity, JavaFX for modern applications, layout managers, events, and the threading rule you must not…

Nov 4, 2026 4 min read

Java

Java Database Connectivity (JDBC)

Connecting to a database from Java with JDBC: prepared statements, try-with-resources, transactions, connection pooling, and when to use JPA instead.

Nov 4, 2026 4 min read

Java

Java Collections Framework

Lists, sets, maps and queues in Java: which to choose, how they differ in speed, and the mistakes that cause ConcurrentModificationException and…

Nov 3, 2026 4 min read

Java

Java Web Development

How a Java web application is put together: servlets, Spring Boot, REST endpoints, templates, database access and what to configure before deploying.

Oct 29, 2026 4 min read

Java

Java Security

The security work that matters in Java applications: SQL injection, deserialization, dependency vulnerabilities, password hashing, XML parsing and secrets handling.

Oct 28, 2026 5 min read

Where to go next

Programming Basics The ideas every language shares — variables, loops, functions and how a program actually runs. 17 guides Python Plain-English Python guides, from your first line of code to small programs that do real work. 77 guides JavaScript How JavaScript works in the browser, explained with short examples you can paste and run. 35 guides

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