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Java

The JVM language behind a huge share of enterprise software.

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This course has 5 lessons. Start with the first one and use the next / previous links at the bottom of each lesson — the sidebar keeps the whole course in order.

Lessons

  1. Java: getting startedHow the JDK, JVM and bytecode fit together, and the smallest program you can compile and run.
  2. Java types and variablesPrimitives versus objects, autoboxing traps, and the equality rules that decide whether two values are 'the same'.
  3. Java collectionsList, Set and Map — which implementation to pick, and why the interface you declare matters more than the class you use.
  4. Exceptions and try-with-resourcesChecked versus unchecked exceptions, how to catch and rethrow well, and closing resources without leaks.
  5. Classes, records and interfacesConstructors, access modifiers, inheritance, and the modern shortcuts — records, enums and interfaces with defaults.

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Last refreshed 2026-09-17.