Learn Java

Write your first Java program — understand the boilerplate, System.out.println, comments, and how Java compiles and runs.

Declare variables in Java — types, assignment, naming rules, var, and the difference between primitives and references.

Java's 8 primitive types, the String class, type casting, autoboxing, and wrapper classes.

Master Java String methods, String.format, StringBuilder for efficient building, and the String pool.

Comparison operators, logical operators, if/else, switch expressions, and the ternary operator.

for, while, do-while, enhanced for-each, break, continue, and labeled loops — control repetition in Java.

Java arrays — declaration, initialisation, traversal, multi-dimensional arrays, and the Arrays utility class.

Define and call methods, parameters, return types, method overloading, varargs, recursion, and static vs instance methods.

Create classes, constructors, instance fields, methods, this keyword, and the difference between classes and objects.

Access modifiers, private fields, getters and setters, data validation, and why hiding implementation details matters.

Extend classes with extends, use super, override methods, understand the Object class, and build class hierarchies.

Define interfaces, implement multiple interfaces, default methods, functional interfaces, and the Comparable/Comparable pattern.

Method overriding, dynamic dispatch, upcasting and downcasting, and how polymorphism makes code flexible and extensible.

Write type-safe reusable code with generics — generic classes, methods, bounded types, wildcards, and the Collections API.

try/catch/finally, checked vs unchecked exceptions, custom exception classes, multi-catch, and best practices.

ArrayList, LinkedList, HashMap, HashSet, TreeMap, Queue, Stack, and the Collections utility class.

Lambda expressions, method references, and the Stream API — filter, map, reduce, collect, sorted, and parallel streams.

Organise code with packages, import statements, access modifiers in the context of packages, and Java module system basics.

Read and write files using java.nio.file.Files, Path, BufferedReader/Writer, and try-with-resources.

Threads, Runnable, ExecutorService, synchronized, volatile, Future, and CompletableFuture for concurrent Java programs.

Make HTTP requests with Java's built-in HttpClient, parse JSON responses, build REST clients, and handle async HTTP.

Records, sealed classes, pattern matching, text blocks, var, switch expressions, and what's new in Java 14-21.