public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

package com.limengxiang.basics.dao;

import com.limengxiang.basics.model.UserModel;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;

import java.util.List;

@Mapper
public interface UserDAO {

    public Integer insert(@Param("username") String username, @Param("mobile") String mobile);

    public UserModel selectOne(@Param("tableName") String tableName, @Param("id") Integer id);

    public List<UserModel> fuzzySearch(@Param("username") String username, @Param("mobile") String mobile);

    public List<UserModel> searchByUsernameOrMobile(@Param("username") String username, @Param("mobile") String mobile);
}

package com.limengxiang.basics.model;

public class UserModel {
    private String username;
    private String mobile;

    public String toString() {
        return "username:" + username +
                ", mobile:" + mobile;
    }
}

package com.limengxiang.basics;

import com.limengxiang.basics.dao.UserDAO;
import com.limengxiang.basics.model.UserModel;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class MybatisDemo {
    public static void main(String[] args) {
        try {
            InputStream stream = Resources.getResourceAsStream("mybatis-config.xml");
            SqlSession sqlSession = new SqlSessionFactoryBuilder().build(stream).openSession(true);
            UserDAO userDAO = sqlSession.getMapper(UserDAO.class);
            // 插入数据
            Integer inserted = userDAO.insert("allen", "13356986723");
            System.out.println("Insert result:" + inserted);
            inserted = userDAO.insert("alfred", "13856986723");
            System.out.println("Insert result:" + inserted);

            UserModel user = userDAO.selectOne("users", 1);
            System.out.println("Select one:" + user);

            List<UserModel> users = userDAO.fuzzySearch("all%", "");
            System.out.println("Fuzzy search by username:" + users);

            users = userDAO.fuzzySearch("", "133%");
            System.out.println("Fuzzy search by mobile:" + users);


            users = userDAO.fuzzySearch("all%", "133%");
            System.out.println("Fuzzy search by username and mobile:" + users);

            users = userDAO.searchByUsernameOrMobile("all%", "135%");
            System.out.println("Search by username:" + users);

            users = userDAO.searchByUsernameOrMobile("", "135%");
            System.out.println("Search by mobile:" + users);

        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

public class HelloWorld {

    public void hello(String name) {
        System.out.println("Hello, " + name);
    }

    public void hello(int age) {
        if (age < 20) {
            System.out.println("Hello son");
        } else if (age >= 20 && age < 40) {
            System.out.println("Hello buddy");
        } else if (age >= 40) {
            System.out.println("Hello old man");
        } else {
            System.out.println("Hello, you are " + age + " years old");
        }
    }

    /**
     * 声明该方法会导致编译时报错
     * error: method hello(int) is already defined in class HelloWorld
     * 返回值类型不是签名的组成部分
     */
//    public int hello(int age) {
//        return age;
//    }

    public static void main(String[] args) {
        System.out.println("Hello, World!");
        HelloWorld hw = new HelloWorld();
        hw.hello("Tom");
        hw.hello(60);
    }
}
输出结果
Hello, World!
Hello, Tom
Hello old man

public class HelloWorld {

    class Person {
        private String name;
        private int age;

        public Person(String name, int age) {
            this.name = name;
            this.age = age;
        }

        public String toString() {
            return name + ", " + age + " years old";
        }
    }

    public void hello(Person person) {
        System.out.println("Hello, " + person);
    }

    public void helloPerson(String name, int age) {
        Person person = new Person(name, age);
        hello(person);
    }

    public static void main(String[] args) {
        System.out.println("Hello, World!");
        HelloWorld hw = new HelloWorld();
        hw.helloPerson("Tom", 25);
    }
}
输出结果
Hello, World!
Hello, Tom, 25 years old

import java.util.ArrayList;

class ThreadDemo {
    class MyThread extends Thread {

        private int id;

        MyThread(int id) {
            this.id = id;
        }

        /**
         * 线程的业务逻辑
         */
        @Override
        public void run() {
            System.out.println("Thread #" + id);
        }
    }

    public void run(int num) {
        // 声明一个MyThread数组
        ArrayList<MyThread> threads = new ArrayList<MyThread>();
        for (int i=0; i<num; i++) {
            threads.add(new MyThread(i));
        }
        // Java版 foreach
        for (MyThread th : threads) {
            th.start();
        }
    }

    public static void main(String[] args) {
        ThreadDemo demo = new ThreadDemo();
        // 启动10个线程
        demo.run(10);
    }
}
输出
Thread #1
Thread #7
Thread #6
Thread #9
Thread #5
Thread #4
Thread #3
Thread #0
Thread #2
Thread #8

import java.util.ArrayList;

class ThreadDemo1 {

    private int counter;

    public ThreadDemo1(int cnt) {
        counter = cnt;
    }

    public int getCounter() {
        return counter;
    }

    public void setCounter(int counter) {
        this.counter = counter;
    }

    class MyThread extends Thread {

        private int id;

        MyThread(int id) {
            this.id = id;
        }

        /**
         * 线程的业务逻辑
         */
        @Override
        public void run() {
            System.out.println("Thread #" + id);
            setCounter(getCounter() + 1);
        }
    }

    public void run(int num) {
        ArrayList<MyThread> threads = new ArrayList<MyThread>();
        for (int i=0; i<num; i++) {
            threads.add(new MyThread(i));
        }
        // Java版 foreach
        for (MyThread th : threads) {
            th.start();
        }
        // join使主线程等待线程结束
        for (MyThread th : threads) {
            try {
                th.join();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        ThreadDemo1 demo1 = new ThreadDemo1(0);
        // 启动多个线程，计数器的值应等于线程数量，否则就有写冲突
        demo1.run(150);
        System.out.println("Counter final:" + demo1.getCounter());
    }
}
输出
... ...
Counter final:149

class ThreadDemo1 {

    private int counter;
    private ReentrantLock lock;

    public ThreadDemo1(int cnt) {
        counter = cnt;
        lock = new ReentrantLock();
    }

    public int getCounter() {
        return counter;
    }

    public void setCounter(int counter) {
        this.counter = counter;
    }

    class MyThread extends Thread {

        private int id;

        MyThread(int id) {
            this.id = id;
        }

        /**
         * 线程的业务逻辑
         */
        @Override
        public void run() {
            // 加锁
            lock.lock();
            System.out.println("Thread #" + id);
            setCounter(getCounter() + 1);
            // 解锁
            lock.unlock();
        }
    }
    // 以下代码与上面的demo相同，省略
}

package com.limengxiang.basics;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.ComponentScan;

/**
 * SpringBootApplication注解告知框架这是启动类
 * ComponentScan注解告知框架需要扫描的组件位置
 * 这里告知框架扫描controller包下面的所有组件，确保HelloController被扫描
 */

@SpringBootApplication
@ComponentScan("com.limengxiang.basics.controller")
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class);
    }
}

package com.limengxiang.basics.controller;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpServletRequest;
import java.util.Map;

/**
 * RestController注解告知框架这是一个提供Restful API的组件
 */
@RestController
public class HelloController {

    /**
     * 框架自动获取请求参数传给方法
     * name参数必传
     * RequestMapping是路由映射注解，可以指定请求路径和请求方法
     *
     * @param name
     * @return
     */
    @RequestMapping(value = "/hello", method = RequestMethod.GET)
    public String hello(@RequestParam("name") String name) {
        return "Hello, " + name;
    }

    /**
     * 手动从request对象中获取参数
     * 框架自动解决依赖，注入request对象
     *
     * @param request
     * @return
     */
    @RequestMapping(value = "/params", method = RequestMethod.POST)
    public Map params(HttpServletRequest request) {
        // 获取一个参数
        String name = request.getParameter("name");
        System.out.println("param name:" + name);
        // 获取所有参数
        Map paramMap = request.getParameterMap();
        System.out.println("param map:" + paramMap);

        return paramMap;
    }
}

package com.limengxiang.basics.dao;

import com.limengxiang.basics.model.UserModel;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import static org.junit.jupiter.api.Assertions.*;

class UserDAOTest {

    private UserDAO dao;

    @BeforeEach
    void setUp() throws IOException {
        if (dao == null) {
            InputStream stream = Resources.getResourceAsStream("mybatis-config.xml");
            SqlSession session = new SqlSessionFactoryBuilder().build(stream).openSession(true);
            dao = session.getMapper(UserDAO.class);
        }
    }

    @Test
    void insert() {
        // 插入数据
        Integer inserted = dao.insert("allen", "13356986723");
        assertEquals(inserted, 1);
    }

    @Test
    void selectOne() {
        UserModel user = dao.selectOne("users", 1);
        System.out.println("Select one:" + user);
    }

    @Test
    void fuzzySearch() {
        List<UserModel> users = dao.fuzzySearch("all%", "");
        System.out.println("Fuzzy search by username:" + users);
    }

    @Test
    void searchByUsernameOrMobile() {
        List<UserModel> users;
        users = dao.searchByUsernameOrMobile("all%", "135%");
        System.out.println("Search by username:" + users);

        users = dao.searchByUsernameOrMobile("", "135%");
        System.out.println("Search by mobile:" + users);
    }
}