java-fundamentals

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Java Fundamentals Skill

Java基础编程Skill

Master core Java programming with production-quality patterns.

掌握符合生产级规范的核心Java编程。

Overview

概述

This skill covers Java fundamentals including syntax, OOP, collections, streams API, and exception handling for Java 8-21.

本Skill涵盖Java 8-21的核心基础知识，包括语法、OOP、集合、Streams API和异常处理。

When to Use This Skill

适用场景

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

当你需要以下操作时使用：

编写简洁、规范的Java代码
遵循OOP原则设计类
选择合适的集合类型
实现函数式编程模式
正确处理异常

Topics Covered

涵盖主题

Core Syntax (Java 8-21)

核心语法（Java 8-21）

Variables, data types, operators
Control flow, methods, classes
Records (Java 16+), sealed classes (Java 17+)
Pattern matching (Java 21)

变量、数据类型、运算符
控制流、方法、类
Records（Java 16+）、密封类（Java 17+）
模式匹配（Java 21）

Object-Oriented Programming

面向对象编程

Classes, inheritance, polymorphism
Interfaces and abstract classes
SOLID principles

类、继承、多态
接口和抽象类
SOLID原则

Collections Framework

集合框架

List: ArrayList, LinkedList
Set: HashSet, TreeSet
Map: HashMap, ConcurrentHashMap
Queue: ArrayDeque, PriorityQueue

List：ArrayList、LinkedList
Set：HashSet、TreeSet
Map：HashMap、ConcurrentHashMap
Queue：ArrayDeque、PriorityQueue

Streams API

filter, map, flatMap, reduce, collect
Optional handling
Parallel streams

filter、map、flatMap、reduce、collect
Optional处理
并行流

Exception Handling

异常处理

Checked vs unchecked exceptions
Try-with-resources
Custom exceptions

受检异常与非受检异常
try-with-resources
自定义异常

Quick Reference

快速参考

java

// 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");

java

// 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

集合选择指南

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

需求	选择	原因
索引访问	ArrayList	O(1)随机访问
唯一元素	HashSet	O(1)存在性检查
排序唯一元素	TreeSet	O(log n)排序
键值对	HashMap	O(1)获取/存入

Troubleshooting

故障排查

Problem	Cause	Solution
NullPointerException	Null reference	Use Optional
ConcurrentModificationException	Modify during iteration	Iterator.remove()
ClassCastException	Wrong type	Use generics

问题	原因	解决方案
NullPointerException	空引用	使用Optional
ConcurrentModificationException	迭代期间修改	使用Iterator.remove()
ClassCastException	类型错误	使用泛型

Usage

使用方法

Skill("java-fundamentals")

Skill("java-fundamentals")