程序员必须要知道的编程范式，你掌握了吗？

public class CommandExample {    public static void main(String[] args) {        int num1 = 5;        int num2 = 10;        int sum = 0;        // 计算两个数的和        sum = num1 + num2;        // 打印结果        System.out.println("Sum: " + sum);    }}

// 定义一个汽车类class Car {    private String brand;    private String color;    public Car(String brand, String color) {        this.brand = brand;        this.color = color;    }    public void start() {        System.out.println("The " + color + " " + brand + " car starts.");    }    public void stop() {        System.out.println("The " + color + " " + brand + " car stops.");    }}public class OOPExample {    public static void main(String[] args) {        // 创建一个Car对象        Car myCar = new Car("Toyota", "Red");        // 调用对象的方法        myCar.start();        myCar.stop();    }}

import java.util.Arrays;import java.util.List;public class FPExample {    public static void main(String[] args) {        // 创建一个字符串列表        List words = Arrays.asList("apple", "banana", "orange", "pear");        // 使用函数式编程方式进行操作        words.stream()             .filter(word -> word.length() > 5) // 过滤长度大于5的单词             .map(String::toUpperCase) // 将单词转换为大写             .forEach(System.out::println); // 打印结果    }}

-- 创建一个示例表CREATE TABLE students (  id INT PRIMARY KEY,  name VARCHAR(50),  age INT);-- 查询年龄小于20岁的学生姓名SELECT name FROM students WHERE age < 20;

% 定义一些逻辑规则和事实parent(john, jim).parent(john, ann).parent(jim, lisa).parent(lisa, mary).% 定义一个递归规则，判断某人是否是某人的祖先ancestor(X, Y) :- parent(X, Y).ancestor(X, Y) :- parent(X, Z), ancestor(Z, Y).% 查询某人的祖先?- ancestor(john, mary).

public class ConcurrentExample {    public static void main(String[] args) {        // 创建一个共享的计数器对象        Counter counter = new Counter();        // 创建多个线程并发执行增加计数的操作        Thread thread1 = new Thread(() -> {            for (int i = 0; i  {            for (int i = 0; i < 1000; i++) {                counter.increment();            }        });        // 启动线程        thread1.start();        thread2.start();        // 等待线程执行完毕        try {            thread1.join();            thread2.join();        } catch (InterruptedException e) {            e.printStackTrace();        }        // 输出计数器的值        System.out.println("Counter value: " + counter.getValue());    }}class Counter {    private int value = 0;    public void increment() {        value++;    }    public int getValue() {        return value;    }}

public class GenericExample {    private T value;    public GenericExample(T value) {        this.value = value;    }    public T getValue() {        return value;    }    public void setValue(T value) {        this.value = value;    }    public static  void printArray(E[] array) {        for (E element : array) {            System.out.println(element);        }    }    public static void main(String[] args) {        GenericExample example1 = new GenericExample("Hello");        System.out.println(example1.getValue());        GenericExample example2 = new GenericExample(123);        System.out.println(example2.getValue());        Integer[] numbers = {1, 2, 3, 4, 5};        printArray(numbers);        String[] words = {"apple", "banana", "cherry"};        printArray(words);    }}

public class UserService {    public void saveUser(User user) {        // 保存用户信息的业务逻辑        // ...    }}

@Aspectpublic class LoggingAspect {    @Before("execution(* com.example.UserService.saveUser(..))")    public void beforeSaveUser(JoinPoint joinPoint) {        // 在saveUser方法执行之前执行的通知        System.out.println("Before saving user: " + joinPoint.getArgs()[0]);    }}

@Configuration@EnableAspectJAutoProxypublic class AppConfig {    // 配置其他组件和Bean    // ...}

public static void main(String[] args) {    AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);    UserService userService = context.getBean(UserService.class);    User user = new User("John Doe");    userService.saveUser(user);}

implementation 'io.reactivex.rxjava3:rxjava:3.1.2'

import io.reactivex.rxjava3.core.Observer;import io.reactivex.rxjava3.disposables.Disposable;public class LoginObserver implements Observer {    @Override    public void onSubscribe(Disposable d) {        // 当观察者订阅时执行的操作    }    @Override    public void onNext(User user) {        // 用户登录成功后执行的操作        String welcomeMessage = "Welcome, " + user.getUsername();        System.out.println(welcomeMessage);    }    @Override    public void onError(Throwable e) {        // 处理错误的操作    }    @Override    public void onComplete() {        // 用户登录完成后执行的操作    }}

import io.reactivex.rxjava3.core.Flowable;public class LoginFlow {    private Flowable loginFlow;    public LoginFlow() {        // 创建登录流        loginFlow = Flowable.create(emitter -> {            // 模拟用户登录过程            // ...            // 当用户登录成功后，发射用户信息            User user = new User("John Doe");            emitter.onNext(user);            // 完成登录流            emitter.onComplete();        }, BackpressureStrategy.BUFFER);    }    public Flowable getLoginFlow() {        return loginFlow;    }}

public static void main(String[] args) {    LoginFlow loginFlow = new LoginFlow();    Flowable loginStream = loginFlow.getLoginFlow();    // 订阅登录流并处理事件    loginStream.subscribe(new LoginObserver());}

public interface Shape {    void draw();}

public class Rectangle implements Shape {    @Override    public void draw() {        System.out.println("Drawing a rectangle");    }}public class Circle implements Shape {    @Override    public void draw() {        System.out.println("Drawing a circle");    }}

import java.util.ArrayList;import java.util.List;public class Canvas implements Shape {    private List shapes;    public Canvas() {        shapes = new ArrayList();    }    public void addShape(Shape shape) {        shapes.add(shape);    }    @Override    public void draw() {        System.out.println("Drawing canvas:");        for (Shape shape : shapes) {            shape.draw();        }    }}

public static void main(String[] args) {    Canvas canvas = new Canvas();    canvas.addShape(new Rectangle());    canvas.addShape(new Circle());    canvas.draw();}

Drawing canvas:Drawing a rectangleDrawing a circle

import java.util.ArrayList;import java.util.List;public class Button {    private List listeners;    public Button() {        listeners = new ArrayList();    }    public void addActionListener(ActionListener listener) {        listeners.add(listener);    }    public void click() {        System.out.println("Button clicked");        // 触发按钮点击事件        for (ActionListener listener : listeners) {            listener.onActionPerformed(new ActionEvent(this));        }    }}

public class TextBox implements ActionListener {    @Override    public void onActionPerformed(ActionEvent event) {        System.out.println("Text box updated: " + event.getSource());    }}

public static void main(String[] args) {    Button button = new Button();    TextBox textBox = new TextBox();    button.addActionListener(textBox);    // 模拟用户点击按钮    button.click();}

Button clickedText box updated: Button@2c8d66b2