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

// Record (Java 16+)
public record User(String name, String email) {}

// Pattern matching (Java 21)
String format(Object obj) {
    return switch (obj) {
        case Integer i -> "Int: %d".formatted(i);
        case String s -> "String: %s".formatted(s);
        default -> obj.toString();
    };
}

// Stream operations
List<String> names = users.stream()
    .filter(User::isActive)
    .map(User::getName)
    .sorted()
    .toList();

// Optional handling
String name = Optional.ofNullable(user)
    .map(User::getName)
    .orElse("Unknown");

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

Skill("java-fundamentals")