📖 Java速查手册

下面是Java速查手册的一个大纲，涵盖了基本语法、常用类和方法、异常处理等内容。这样的手册对初学者和有经验的开发者都非常有用，可以节省查找文档和在线搜索的时间。

1. 基本语法

1.1 数据类型

基本数据类型：

byte b = 127;
short s = 32767;
int i = 2147483647;
long l = 9223372036854775807L;
float f = 3.14f;
double d = 3.141592653589793;
char c = 'A';
boolean bool = true;

引用数据类型：

String str = "Hello, World!";
int[] arr = {1, 2, 3, 4, 5};

1.2 变量与常量

变量声明：

int a = 10;

常量声明：

final int CONSTANT = 100;

1.3 运算符

算术运算符：

int sum = a + b;
int diff = a - b;
int product = a * b;
int quotient = a / b;
int remainder = a % b;

比较运算符：

boolean isEqual = (a == b);
boolean isNotEqual = (a != b);
boolean isGreater = (a > b);
boolean isLesser = (a < b);
boolean isGreaterOrEqual = (a >= b);
boolean isLesserOrEqual = (a <= b);

逻辑运算符：

boolean and = (a > b && c > d);
boolean or = (a > b || c > d);
boolean not = !(a > b);

1.4 控制结构

条件语句：

if (a > b) {
    System.out.println("a is greater than b");
} else if (a < b) {
    System.out.println("a is less than b");
} else {
    System.out.println("a is equal to b");
}

循环语句：

// for循环
for (int i = 0; i < 10; i++) {
    System.out.println(i);
}

// while循环
int i = 0;
while (i < 10) {
    System.out.println(i);
    i++;
}

// do-while循环
int j = 0;
do {
    System.out.println(j);
    j++;
} while (j < 10);

2. 面向对象编程

2.1 类与对象

类的定义：

public class Person {
    private String name;
    private int age;

    // 构造方法
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    // Getter和Setter方法
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    // 普通方法
    public void introduce() {
        System.out.println("Hi, my name is " + name + " and I am " + age + " years old.");
    }
}

对象的创建：

Person person = new Person("Alice", 30);
person.introduce();

2.2 继承

继承的使用：

public class Student extends Person {
    private String studentId;

    public Student(String name, int age, String studentId) {
        super(name, age);
        this.studentId = studentId;
    }

    public String getStudentId() {
        return studentId;
    }

    public void setStudentId(String studentId) {
        this.studentId = studentId;
    }

    @Override
    public void introduce() {
        super.introduce();
        System.out.println("My student ID is " + studentId);
    }
}

2.3 多态

多态的使用：

public class Animal {
    public void makeSound() {
        System.out.println("Some generic animal sound");
    }
}

public class Dog extends Animal {
    @Override
    public void makeSound() {
        System.out.println("Bark");
    }
}

public class Cat extends Animal {
    @Override
    public void makeSound() {
        System.out.println("Meow");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal myDog = new Dog();
        Animal myCat = new Cat();
        myDog.makeSound(); // 输出：Bark
        myCat.makeSound(); // 输出：Meow
    }
}

3. 常用类与方法

3.1 字符串处理

字符串拼接：

String greeting = "Hello" + " " + "World!";

字符串长度：

int length = greeting.length();

字符串比较：

boolean isEqual = greeting.equals("Hello World!");

子字符串：

String subStr = greeting.substring(0, 5);

3.2 集合框架

ArrayList：

List<String> list = new ArrayList<>();
list.add("Apple");
list.add("Banana");
list.add("Cherry");

for (String fruit : list) {
    System.out.println(fruit);
}

HashMap：

Map<String, Integer> map = new HashMap<>();
map.put("Apple", 1);
map.put("Banana", 2);
map.put("Cherry", 3);

for (Map.Entry<String, Integer> entry : map.entrySet()) {
    System.out.println(entry.getKey() + ": " + entry.getValue());
}

4. 异常处理

4.1 try-catch块

基本用法：

try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println("Cannot divide by zero");
}

4.2 自定义异常

定义和使用自定义异常：

public class CustomException extends Exception {
    public CustomException(String message) {
        super(message);
    }
}

public class Main {
    public static void main(String[] args) {
        try {
            throw new CustomException("This is a custom exception");
        } catch (CustomException e) {
            System.out.println(e.getMessage());
        }
    }
}

5. 输入输出（I/O）

5.1 文件操作

读取文件：

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class FileReadExample {
    public static void main(String[] args) {
        try (BufferedReader br = new BufferedReader(new FileReader("example.txt"))) {
            String line;
            while ((line = br.readLine()) != null) {
                System.out.println(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

写入文件：

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;

public class FileWriteExample {
    public static void main(String[] args) {
        try (BufferedWriter bw = new BufferedWriter(new FileWriter("example.txt"))) {
            bw.write("Hello, World!");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

6. 并发编程

6.1 创建线程

继承Thread类：

public class MyThread extends Thread {
    @Override
    public void run() {
        System.out.println("Thread is running");
    }
}

public class Main {
    public static void main(String[] args) {
        MyThread thread = new MyThread();
        thread.start();
    }
}

实现Runnable接口：

public class MyRunnable implements Runnable {
    @Override
    public void run() {
        System.out.println("Thread is running");
    }
}

public class Main {
    public static void main(String[] args) {
        Thread thread = new Thread

好的，下面是Java速查手册的继续部分。

6. 并发编程 (续)

6.1 创建线程

实现Runnable接口：

public class MyRunnable implements Runnable {
    @Override
    public void run() {
        System.out.println("Thread is running");
    }
}

public class Main {
    public static void main(String[] args) {
        Thread thread = new Thread(new MyRunnable());
        thread.start();
    }
}

6.2 并发工具类

ExecutorService：

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Main {
    public static void main(String[] args) {
        ExecutorService executorService = Executors.newFixedThreadPool(2);
        
        executorService.submit(new MyRunnable());
        executorService.submit(new MyRunnable());
        
        executorService.shutdown();
    }
}

CountDownLatch：

import java.util.concurrent.CountDownLatch;

public class Worker implements Runnable {
    private CountDownLatch latch;

    public Worker(CountDownLatch latch) {
        this.latch = latch;
    }

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName() + " is working");
        try {
            Thread.sleep((int) (Math.random() * 1000));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        latch.countDown();
        System.out.println(Thread.currentThread().getName() + " finished working");
    }
}

public class Main {
    public static void main(String[] args) {
        CountDownLatch latch = new CountDownLatch(3);

        new Thread(new Worker(latch)).start();
        new Thread(new Worker(latch)).start();
        new Thread(new Worker(latch)).start();

        try {
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("All workers finished. Main thread continues.");
    }
}

7. 网络编程

7.1 创建服务器

简单服务器：

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;

public class SimpleServer {
    public static void main(String[] args) {
        try (ServerSocket serverSocket = new ServerSocket(8080)) {
            System.out.println("Server is listening on port 8080");

            while (true) {
                Socket socket = serverSocket.accept();
                System.out.println("New client connected");
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

7.2 创建客户端

简单客户端：

import java.io.IOException;
import java.net.Socket;

public class SimpleClient {
    public static void main(String[] args) {
        try (Socket socket = new Socket("localhost", 8080)) {
            System.out.println("Connected to the server");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

8. 数据库操作

8.1 使用JDBC连接数据库

连接数据库：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class DatabaseConnection {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydatabase";
        String user = "root";
        String password = "password";

        try (Connection conn = DriverManager.getConnection(url, user, password)) {
            if (conn != null) {
                System.out.println("Connected to the database");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

8.2 执行SQL查询

查询数据：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class DatabaseQuery {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydatabase";
        String user = "root";
        String password = "password";

        try (Connection conn = DriverManager.getConnection(url, user, password);
             Statement stmt = conn.createStatement()) {

            String sql = "SELECT id, name, age FROM users";
            ResultSet rs = stmt.executeQuery(sql);

            while (rs.next()) {
                int id = rs.getInt("id");
                String name = rs.getString("name");
                int age = rs.getInt("age");

                System.out.println("ID: " + id + ", Name: " + name + ", Age: " + age);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

8.3 更新数据

更新数据：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

public class DatabaseUpdate {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydatabase";
        String user = "root";
        String password = "password";

        try (Connection conn = DriverManager.getConnection(url, user, password);
             Statement stmt = conn.createStatement()) {

            String sql = "UPDATE users SET age = 30 WHERE id = 1";
            int rowsAffected = stmt.executeUpdate(sql);

            System.out.println("Rows affected: " + rowsAffected);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

8.4 插入数据

插入数据：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

public class DatabaseInsert {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydatabase";
        String user = "root";
        String password = "password";

        try (Connection conn = DriverManager.getConnection(url, user, password);
             Statement stmt = conn.createStatement()) {

            String sql = "INSERT INTO users (name, age) VALUES ('John Doe', 25)";
            int rowsAffected = stmt.executeUpdate(sql);

            System.out.println("Rows affected: " + rowsAffected);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

8.5 删除数据

删除数据：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

public class DatabaseDelete {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydatabase";
        String user = "root";
        String password = "password";

        try (Connection conn = DriverManager.getConnection(url, user, password);
             Statement stmt = conn.createStatement()) {

            String sql = "DELETE FROM users WHERE id = 1";
            int rowsAffected = stmt.executeUpdate(sql);

            System.out.println("Rows affected: " + rowsAffected);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

9. 网络编程

9.1 创建服务器

简单服务器：

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;

public class SimpleServer {
    public static void main(String[] args) {
        try (ServerSocket serverSocket = new ServerSocket(8080)) {
            System.out.println("Server is listening on port 8080");

            while (true) {
                Socket socket = serverSocket.accept();
                System.out.println("New client connected");
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

9.2 创建客户端

简单客户端：

import java.io.IOException;
import java.net.Socket;

public class SimpleClient {
    public static void main(String[] args) {
        try (Socket socket = new Socket("localhost", 8080)) {
            System.out.println("Connected to the server");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

10. Web开发

10.1 创建Servlet

简单Servlet：

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/hello")
public class HelloServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("<html><body>");
        out.println("<h1>Hello, World!</h1>");
        out.println("</body></html>");
    }
}

10.2 创建JSP页面

简单JSP页面：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>JSP Example</title>
</head>
<body>
    <h1>Hello, JSP!</h1>
    <%
        // 在JSP中嵌入Java代码
        String message = "Welcome to JSP!";
        out.println("<p>" + message + "</p>");
    %>
</body>
</html>

10.3 Spring Boot

创建Spring Boot应用主类：

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class MyApp {
    public static void main(String[] args) {
        SpringApplication.run(MyApp.class, args);
    }
}

创建一个简单的REST控制器：

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/api")
public class GreetingController {
    @GetMapping("/greeting")
    public String greeting() {
        return "Hello, RESTful Web Service!";
    }
}

配置文件（application.properties）：

server.port=8080

10.4 Spring MVC

创建控制器类：

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
@RequestMapping("/home")
public class HomeController {
    @GetMapping
    public String home(Model model) {
        model.addAttribute("message", "Welcome to Spring MVC!");
        return "home";
    }
}

创建视图模板（home.html）：

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <title>Home</title>
</head>
<body>
    <h1 th:text="${message}">Welcome to Spring MVC!</h1>
</body>
</html>

11. 测试

11.1 使用JUnit

创建一个简单的JUnit测试：

import static org.junit.jupiter.api.Assertions.assertEquals;
import org.junit.jupiter.api.Test;

public class CalculatorTest {
    @Test
    public void testAddition() {
        Calculator calculator = new Calculator();
        int result = calculator.add(2, 3);
        assertEquals(5, result, "2 + 3 should equal 5");
    }
}

class Calculator {
    public int add(int a, int b) {
        return a + b;
    }
}

11.2 使用Mockito

创建一个Mockito测试：

import static org.mockito.Mockito.*;
import org.junit.jupiter.api.Test;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;

public class UserServiceTest {
    @Mock
    private UserRepository userRepository;

    @InjectMocks
    private UserService userService;

    @Test
    public void testFindUserById() {
        MockitoAnnotations.openMocks(this);
        User user = new User("John");
        when(userRepository.findById(1L)).thenReturn(Optional.of(user));

        User result = userService.findUserById(1L);
        assertEquals("John", result.getName());
    }
}

class User {
    private String name;
    public User(String name) {
        this.name = name;
    }
    public String getName() {
        return name;
    }
}

interface UserRepository {
    Optional<User> findById(Long id);
}

class UserService {
    private UserRepository userRepository;
    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }
    public User findUserById(Long id) {
        return userRepository.findById(id).orElse(null);
    }
}

12. 常见问题

12.1 NullPointerException

处理NullPointerException：

String str = null;
if (str != null) {
    System.out.println(str.length());
} else {
    System.out.println("String is null");
}

12.2 ClassCastException

处理ClassCastException：

Object obj = "Hello";
if (obj instanceof Integer) {
    Integer num = (Integer) obj;
} else {
    System.out.println("Object is not an Integer");
}

12.3 ArrayIndexOutOfBoundsException

处理ArrayIndexOutOfBoundsException：

int[] arr = {1, 2, 3};
int index = 3;
if (index >= 0 && index < arr.length) {
    System.out.println(arr[index]);
} else {
    System.out.println("Index is out of bounds");
}

📖 Java速查手册

1. 基本语法

1.1 数据类型

1.2 变量与常量

1.3 运算符

1.4 控制结构

2. 面向对象编程

2.1 类与对象

2.2 继承

2.3 多态

3. 常用类与方法

3.1 字符串处理

3.2 集合框架

4. 异常处理

4.1 try-catch块

4.2 自定义异常

5. 输入输出（I/O）

5.1 文件操作

6. 并发编程

6.1 创建线程

6. 并发编程 (续)

6.1 创建线程

6.2 并发工具类

7. 网络编程

7.1 创建服务器

7.2 创建客户端

8. 数据库操作

8.1 使用JDBC连接数据库

8.2 执行SQL查询

8.3 更新数据

8.4 插入数据

8.5 删除数据

9. 网络编程

9.1 创建服务器

9.2 创建客户端

10. Web开发

10.1 创建Servlet

10.2 创建JSP页面

10.3 Spring Boot

10.4 Spring MVC

11. 测试

11.1 使用JUnit

11.2 使用Mockito

12. 常见问题

12.1 NullPointerException

12.2 ClassCastException

12.3 ArrayIndexOutOfBoundsException

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