引言
Java作为一门经典的面向对象编程语言，自1995年诞生以来，始终保持着旺盛的生命力。无论你是刚刚接触Java的初学者，还是希望巩固基础的开发者，进行一次全面的基础复盘都大有裨益。本文将系统性地梳理Java核心知识点，帮助你构建完整的知识体系。
一、Java开发环境搭建
JDK安装与配置
# 检查Java版本 java -version javac -version# 设置环境变量（示例） JAVA_HOME=/path/to/jdk PATH=$JAVA_HOME/bin:$PATH
二、Java基础语法
变量与数据类型
public class DataTypes {public static void main(String[] args) {// 基本数据类型byte b = 127; // 8位short s = 32767; // 16位int i = 2147483647; // 32位long l = 9223372036854775807L; // 64位float f = 3.14f; // 32位浮点double d = 3.1415926535; // 64位浮点char c = 'A'; // 16位Unicodeboolean bool = true; // 1位// 引用数据类型String str = "Hello Java";int[] array = {1, 2, 3};} }
运算符详解
public class Operators {public static void main(String[] args) {int a = 10, b = 3;// 算术运算符System.out.println(a + b); // 13System.out.println(a - b); // 7System.out.println(a * b); // 30System.out.println(a / b); // 3System.out.println(a % b); // 1// 关系运算符System.out.println(a > b); // trueSystem.out.println(a == b); // false// 逻辑运算符boolean x = true, y = false;System.out.println(x && y); // falseSystem.out.println(x || y); // trueSystem.out.println(!x); // false// 三元运算符int max = (a > b) ? a : b; // 10 } }
流程控制结构
public class ControlFlow {public static void main(String[] args) {// if-else语句int score = 85;if (score >= 90) {System.out.println("优秀");} else if (score >= 80) {System.out.println("良好"); // 输出这个} else {System.out.println("及格");}// switch语句int day = 3;switch (day) {case 1:System.out.println("星期一");break;case 2:System.out.println("星期二");break;case 3:System.out.println("星期三"); // 输出这个break;default:System.out.println("其他");}// 循环结构for (int i = 0; i < 5; i++) {System.out.println("for循环: " + i);}int j = 0;while (j < 3) {System.out.println("while循环: " + j);j++;}int k = 0;do {System.out.println("do-while循环: " + k);k++;} while (k < 3);} }
三、面向对象编程
类与对象
// 类的定义 public class Person {// 字段（属性）private String name;private int age;// 构造方法public Person() {this.name = "未知";this.age = 0;}public Person(String name, int age) {this.name = name;this.age = age;}// 方法public void introduce() {System.out.println("我叫" + name + "，今年" + age + "岁");}// Getter和Setterpublic String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {if (age >= 0) {this.age = age;}} }// 使用类 public class OOPDemo {public static void main(String[] args) {Person person1 = new Person();Person person2 = new Person("张三", 25);person1.introduce(); // 我叫未知，今年0岁person2.introduce(); // 我叫张三，今年25岁 } }
三大特性：封装、继承、多态
// 封装示例 public class BankAccount {private double balance;public void deposit(double amount) {if (amount > 0) {balance += amount;}}public boolean withdraw(double amount) {if (amount > 0 && balance >= amount) {balance -= amount;return true;}return false;}public double getBalance() {return balance;} }// 继承示例 class Animal {protected String name;public Animal(String name) {this.name = name;}public void eat() {System.out.println(name + "在吃东西");} }class Dog extends Animal {public Dog(String name) {super(name);}public void bark() {System.out.println(name + "在汪汪叫");}// 方法重写 @Overridepublic void eat() {System.out.println(name + "在吃狗粮");} }// 多态示例 public class PolymorphismDemo {public static void main(String[] args) {Animal myAnimal = new Dog("旺财");myAnimal.eat(); // 旺财在吃狗粮 - 多态的表现 } }
抽象类与接口
// 抽象类 abstract class Shape {protected String color;public Shape(String color) {this.color = color;}// 抽象方法public abstract double calculateArea();// 具体方法public void displayColor() {System.out.println("颜色: " + color);} }class Circle extends Shape {private double radius;public Circle(String color, double radius) {super(color);this.radius = radius;}@Overridepublic double calculateArea() {return Math.PI * radius * radius;} }// 接口 interface Flyable {void fly(); // 隐式抽象方法default void takeOff() { // 默认方法System.out.println("准备起飞");}static void showFeature() { // 静态方法System.out.println("可以飞行");} }interface Swimmable {void swim(); }// 实现多个接口 class Duck implements Flyable, Swimmable {@Overridepublic void fly() {System.out.println("鸭子在飞行");}@Overridepublic void swim() {System.out.println("鸭子在游泳");} }
四、异常处理
异常体系结构
public class ExceptionHandling {public static void main(String[] args) {// try-catch-finallytry {int result = divide(10, 0);System.out.println("结果: " + result);} catch (ArithmeticException e) {System.out.println("捕获算术异常: " + e.getMessage());} catch (Exception e) {System.out.println("捕获其他异常: " + e.getMessage());} finally {System.out.println("finally块总是执行");}// 抛出异常try {checkAge(15);} catch (IllegalArgumentException e) {System.out.println(e.getMessage());}}public static int divide(int a, int b) {return a / b;}public static void checkAge(int age) {if (age < 18) {throw new IllegalArgumentException("年龄必须大于等于18岁");}System.out.println("年龄验证通过");} }// 自定义异常 class InsufficientBalanceException extends Exception {public InsufficientBalanceException(String message) {super(message);} }class BankAccount {private double balance;public void withdraw(double amount) throws InsufficientBalanceException {if (amount > balance) {throw new InsufficientBalanceException("余额不足，当前余额: " + balance);}balance -= amount;} }
五、集合框架
常用集合类
import java.util.*;public class CollectionDemo {public static void main(String[] args) {// List接口 - 有序可重复List<String> arrayList = new ArrayList<>();arrayList.add("Apple");arrayList.add("Banana");arrayList.add("Apple"); // 允许重复 List<String> linkedList = new LinkedList<>();linkedList.add("Cat");linkedList.add("Dog");// Set接口 - 无序不重复Set<String> hashSet = new HashSet<>();hashSet.add("Red");hashSet.add("Green");hashSet.add("Red"); // 不会重复添加 Set<String> treeSet = new TreeSet<>();treeSet.add("Zoo");treeSet.add("Apple");treeSet.add("Banana");// 自动排序: [Apple, Banana, Zoo]// Map接口 - 键值对Map<String, Integer> hashMap = new HashMap<>();hashMap.put("Alice", 25);hashMap.put("Bob", 30);hashMap.put("Alice", 26); // 更新值 Map<String, Integer> treeMap = new TreeMap<>();treeMap.put("Orange", 5);treeMap.put("Apple", 3);treeMap.put("Banana", 7);// 按键排序: {Apple=3, Banana=7, Orange=5}// 遍历集合for (String fruit : arrayList) {System.out.println(fruit);}for (Map.Entry<String, Integer> entry : hashMap.entrySet()) {System.out.println(entry.getKey() + ": " + entry.getValue());}} }
六、输入输出流
文件操作
import java.io.*; import java.nio.file.*;public class IODemo {public static void main(String[] args) {// 使用File类File file = new File("test.txt");try {// 创建文件if (file.createNewFile()) {System.out.println("文件创建成功");}// 写入文件FileWriter writer = new FileWriter(file);writer.write("Hello Java IO\n");writer.write("这是第二行");writer.close();// 读取文件FileReader reader = new FileReader(file);BufferedReader bufferedReader = new BufferedReader(reader);String line;while ((line = bufferedReader.readLine()) != null) {System.out.println(line);}bufferedReader.close();} catch (IOException e) {e.printStackTrace();}// 使用NIO (Java 7+)try {Path path = Paths.get("test_nio.txt");Files.write(path, Arrays.asList("第一行", "第二行", "第三行"),StandardCharsets.UTF_8);List<String> lines = Files.readAllLines(path, StandardCharsets.UTF_8);for (String text : lines) {System.out.println(text);}} catch (IOException e) {e.printStackTrace();}} }
七、多线程编程
线程创建与同步
public class ThreadDemo {public static void main(String[] args) {// 继承Thread类MyThread thread1 = new MyThread();thread1.start();// 实现Runnable接口Thread thread2 = new Thread(new MyRunnable());thread2.start();// 使用Lambda表达式Thread thread3 = new Thread(() -> {for (int i = 0; i < 5; i++) {System.out.println("Lambda线程: " + i);}});thread3.start();// 线程同步示例Counter counter = new Counter();Thread t1 = new Thread(() -> {for (int i = 0; i < 1000; i++) {counter.increment();}});Thread t2 = new Thread(() -> {for (int i = 0; i < 1000; i++) {counter.increment();}});t1.start();t2.start();try {t1.join();t2.join();} catch (InterruptedException e) {e.printStackTrace();}System.out.println("最终计数: " + counter.getCount());} }class MyThread extends Thread {@Overridepublic void run() {for (int i = 0; i < 5; i++) {System.out.println("继承Thread: " + i);}} }class MyRunnable implements Runnable {@Overridepublic void run() {for (int i = 0; i < 5; i++) {System.out.println("实现Runnable: " + i);}} }// 线程安全计数器 class Counter {private int count = 0;public synchronized void increment() {count++;}public int getCount() {return count;} }
八、Java新特性
Java 8+ 重要特性
import java.util.*; import java.util.stream.*; import java.time.*;public class NewFeatures {public static void main(String[] args) {// Lambda表达式List<String> names = Arrays.asList("Alice", "Bob", "Charlie");// 传统方式Collections.sort(names, new Comparator<String>() {@Overridepublic int compare(String a, String b) {return a.compareTo(b);}});// Lambda方式Collections.sort(names, (a, b) -> a.compareTo(b));// Stream APIList<String> filteredNames = names.stream().filter(name -> name.startsWith("A")).map(String::toUpperCase).collect(Collectors.toList());System.out.println(filteredNames); // [ALICE]// 方法引用 names.forEach(System.out::println);// Optional类 - 避免空指针异常Optional<String> optionalName = Optional.ofNullable(getName());String result = optionalName.orElse("默认名称");System.out.println(result);// 新的日期时间APILocalDate today = LocalDate.now();LocalTime now = LocalTime.now();LocalDateTime currentDateTime = LocalDateTime.now();System.out.println("今天: " + today);System.out.println("现在: " + now);System.out.println("当前日期时间: " + currentDateTime);// 日期计算LocalDate nextWeek = today.plusWeeks(1);Period period = Period.between(today, nextWeek);System.out.println("下周: " + nextWeek);System.out.println("间隔: " + period.getDays() + "天");}private static String getName() {return Math.random() > 0.5 ? "张三" : null;} }
Java的世界博大精深，基础扎实才能在编程道路上走得更远。希望这篇复盘文章能帮助你巩固Java基础，为后续的深入学习打下坚实基础！
