Technology
30 min read
Take the Expense Tracker CLI and add a PostgreSQL repository behind the same interface: an idempotent schema, a transactional bulk import, a connection pool, one shared contract test for every implementation, a fat jar, and an honest review.
Technology
25 min read
Learn JDBC, the standard way Java programs use a relational database: connecting with a driver, running queries with PreparedStatement, mapping rows, preventing SQL injection, transactions, error codes, batching and connection pooling, with every program run against PostgreSQL 18.
Technology
21 min read
Learn the SQL that backend developers use every day on PostgreSQL: tables and constraints, inserting, querying, joining and grouping data, transactions and isolation, indexes and query plans, and normalisation, with every statement run on a real PostgreSQL server.
Technology
29 min read
Build your first complete Java application: a command-line expense tracker with a clear design, money handled correctly, a file-based repository behind an interface, automated tests, a Maven build, and a runnable jar, then review it honestly.
Technology
16 min read
Learn to write reliable unit tests in Java with JUnit: structure, assertions, exception and parameterised tests, test lifecycle, then test doubles and Mockito, and the honest limits of mocking, all run in a real Maven project.
Technology
11 min read
A practical Git workflow for Java developers: the three areas, commits and good messages, branches, merging and resolving conflicts, pull requests, a correct .gitignore for Maven projects, and what to do when a secret is committed.
Technology
15 min read
Learn what a build tool does and how Maven does it: the standard project layout, the pom.xml, dependencies and scopes, transitive dependencies, the build lifecycle, plugins, and the common failures, all checked against a real project.
Technology
18 min read
A method for finding bugs instead of guessing: read compiler errors and stack traces properly, form and test hypotheses, use breakpoints and stepping in a debugger, log usefully at the right level, and reach for thread dumps and heap dumps when the problem is a hang or a leak.
Technology
16 min read
How to read and write files in modern Java with Path and Files, why character encoding matters, how to stream large files safely, how to avoid path traversal, and what Java serialization really is, why it is risky, and what to use instead.
Technology
16 min read
The concurrency tools you should actually use: thread pools with ExecutorService, Callable and Future, producer-consumer with BlockingQueue, ConcurrentHashMap and friends, CompletableFuture pipelines, and virtual threads from Java 21, including what they do and do not do.
Technology
15 min read
Concurrency taught from the problems: lost updates, visibility and deadlock. Threads and the Java Memory Model, race conditions and atomicity, synchronized, volatile, atomic classes and locks, with runnable demonstrations and honest advice on what each tool does and does not guarantee.
Technology
16 min read
A working mental model of the Java Virtual Machine: how classes are loaded and initialised, what lives on the stack and the heap, how garbage collection decides what to free and why memory leaks still happen, and what the JIT compiler does. Each simplification is marked, and common myths are corrected.
Technology
12 min read
Why null causes so many bugs, what Optional is actually for, how to use map, flatMap, orElse, orElseGet and orElseThrow, and the common misuses (fields, parameters, get without a check). Optional is a tool for return values, not a universal replacement for null.
Technology
13 min read
How to process collections declaratively with Java Streams: filter, map, flatMap, sorted, reduce and collect, grouping and partitioning, why streams are lazy and single-use, what parallel streams really cost, and an honest guide to when a plain loop is the better choice.
Technology
12 min read
How Java lets you pass behaviour as a value: lambda expressions, functional interfaces and the standard Predicate, Function, Consumer and Supplier, the four kinds of method reference, composing functions, why captured variables must be effectively final, and how lambdas replace the older anonymous classes.
Technology
13 min read
What the angle brackets mean and why they exist. Generic classes and methods, bounded types, why List of Integer is not a List of Number, wildcards with extends and super, the PECS rule that makes them make sense, and type erasure with its practical consequences.
Technology
12 min read
How to sort objects with Comparable and Comparator, how queues, deques and priority queues work, why ArrayDeque replaces the legacy Stack, and a decision guide with complexity and memory trade-offs for choosing the right collection.
Technology
14 min read
How Java stores key-value pairs, and how HashMap finds a value in constant time: hashing, buckets, collisions, resizing and treeification, explained with a small map you build yourself. Plus LinkedHashMap, TreeMap, the everyday Map methods, and the mistakes that corrupt a map.
