Java Fundamentals Skill Skill

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")

Agent Skills: Java Fundamentals Skill

Skill Files