反射之类的加载器

反射之类的加载器

@Test
    public void test1(){
        //对于自定义类，使用系统类加载器进行加载
        ClassLoader classLoader = ClassLoaderTest.class.getClassLoader();
        System.out.println(classLoader);//系统的加载器
        //调用系统类加载器的getParent()：获取扩展类加载器
        ClassLoader classLoader1 = classLoader.getParent();
        System.out.println(classLoader1);//扩展类加载器

        //调用扩展类加载器的getParent()：无法获取引导类加载器
        //引导类加载器主要负责加载java的核心类库，无法加载自定义类的。
        ClassLoader classLoader2 = classLoader1.getParent();
        System.out.println(classLoader2);//引导类加载器,不能拿到

        ClassLoader loader = String.class.getClassLoader();
        System.out.println(loader);//引导类加载器,不能拿到

    }

    /*
    Properties：用来读取配置文件。
     */
    @Test
    public void test2() throws Exception {
        Properties pros = new Properties();
        //此时的文件默认在当前的module下
        //读取配置文件的方式一：
//        FileInputStream fis = new FileInputStream("src\\jdbc1.properties");
//        pros.load(fis);
        //读取配置文件的方式二：
        //配置文件默认识别为当前module下的src下
//        ClassLoader classLoader = ClassLoaderTest.class.getClassLoader();
//        InputStream ips = classLoader.getResourceAsStream("jdbc1.properties");
//        pros.load(ips);

        String user = pros.getProperty("user");
        String password = pros.getProperty("password");
        System.out.println("user=" + user + ",password=" + password );

    }

反射的动态性的体会

@Test
public void test2(){

    for(int i = 0;i < 100;i++){
        int num = new Random().nextInt(3);//0,1,2
        String classPath = "";
        switch(num){
            case 0:
                classPath = "java.util.Date";
                break;
            case 1:
                classPath = "java.lang.Object";
                break;
            case 2:
                classPath = "com.atguigu.java.Person";
                break;
        }

        try {
            Object obj = getInstance(classPath);
            System.out.println(obj);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }



}

/*
创建一个指定类的对象。
classPath:指定类的全类名
 */
public Object getInstance(String classPath) throws Exception {
    Class clazz =  Class.forName(classPath);
    return clazz.newInstance();
}

Person类

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

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    public Person() {
        System.out.println("无参构造器");
    }

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

    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;
    }

    public void show(){
        System.out.println("hello i am people");
    }

    private String showNation(String nation){
        System.out.println("i am from " + nation);
        return nation;
    }
}