Java Study #2 — Collections (List / Map / Set) · Stream Pipelines · Null-Safe Handling with Optional
Week 2 of studying Java. I go through the core of the Collection Framework — List (ArrayList), Map (HashMap), Set — and notice the 'interface and implementation' pattern in each of them (List<String> books = new ArrayList<>()). Then I move on to Stream, building filter → map → collect pipelines without for loops, method references (System.out::println), and combining groupingBy + counting. Finally, Optional — I learn to always handle the absence-of-value case with ifPresent / orElse / map instead of calling get() right away.
