Master core Java programming - syntax, OOP, collections, streams, and exception handling

Java Fundamentals Skill Master core Java programming with production quality patterns. Overview This skill covers Java fundamentals including syntax, OOP, collections, streams API, and exception handling for Java 8 21. When to Use This Skill Use when you need to: Write clean, idiomatic Java code Design classes following OOP principles Choose appropriate collection types Implement functional programming patterns Handle exceptions properly Topics Covered Core Syntax (Java 8 21) Variables, data types, operators Control flow, methods, classes Records (Java 16+), sealed classes (Java 17+) Pattern matching (Java 21) Object Oriented Programming Classes, inheritance, polymorphism Interfaces and abstract classes SOLID principles Collections Framework List: ArrayList, LinkedList Set: HashSet, TreeSet Map: HashMap, ConcurrentHashMap Queue: ArrayDeque, PriorityQueue Streams API filter, map, flatMap, reduce, collect Optional handling Parallel streams Exception Handling Checked vs unchecked exceptions Try with resources Custom exceptions Quick Reference Collection Selection Need Use Reason Indexed access ArrayList O(1) random access Unique elements HashSet O(1) contains Sorted unique TreeSet O(log n) sorted Key value pairs HashMap O(1) get/put Troubleshooting Problem Cause Solution NullPointerException Null reference Use Optional ConcurrentModificationException Modify during iteration Iterator.remove() ClassCastException Wrong type Use generics Usage

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