一篇文章带你了解一些Java反射的学习记录

// re.properties
className=com.javalearn.reflect.Cat
methodName=hi

public class Cat {
    private String name = "招财猫";
    public void hi() {
        System.out.println("hi:" + this.name);
    }
}

public class ReflectionDemo {
    public static void main(String[] args) throws Exception {
        // 1.properties对象加载配置文件
        Properties properties = new Properties();
        properties.load(new FileInputStream("src/main/resources/re.properties"));
        String className = properties.getProperty("className");
        String methodName = properties.getProperty("methodName");
        System.out.println("类名：" + className);
        System.out.println("方法名：" + methodName);
        // 2.根据类名获取Class类对象
        //  获取Class对象的三种方式：
        //      1.类名.class
        //      2.对象.getClass()
        //      3.Class.forName(类名)
        Class cls = Class.forName(className);
        // 3.生成实例对象
        Object o = cls.newInstance();
        // 4.获取方法
        Method declaredMethod = cls.getDeclaredMethod(methodName);
        // 5.方法.invoke(对象)
        declaredMethod.invoke(o);
        // 6.反射涉及的其他类
        // 6.1Field成员变量
        Field name = cls.getDeclaredField("name");
        name.setAccessible(true);   //private属性需暴力反射
        System.out.println(name.get(o));
        // 6.2Constructor构造器
        Constructor constructor = cls.getConstructor(); //方法参数类型与构造器的参数类型一致，不写就是无参构造器
        Object o1 = constructor.newInstance();
        System.out.println(o1);
    }
}

public class PerformanceDemo {
    public static void main(String[] args) throws Exception {
        tradition();
        reflect();
    }
    private static void reflect() throws Exception {
        Class cls = Class.forName("com.sankuai.yangjin.javalearn.reflect.Cat");
        Object o = cls.newInstance();
        Method hi = cls.getMethod("hi");
        long start = System.currentTimeMillis();
        for (int i = 0; i < 10000; i++) {
            hi.invoke(o);
        }
        long end = System.currentTimeMillis();
        System.out.println("反射耗时：" + (end - start));
    }
    private static void tradition() {
        Cat cat = new Cat();
        long start = System.currentTimeMillis();
        for (int i = 0; i < 10000; i++) {
            cat.hi();
        }
        long end = System.currentTimeMillis();
        System.out.println("传统耗时：" + (end - start));
    }
}

public class LoadDemo {
    public static void main (String[] args) throws Exception {
        Scanner scanner = new Scanner(System.in);
        String num = scanner.next();
        switch (num) {
            case "1":
                // 静态加载
                Dog dog = new Dog();
                break;
            case "2":
                // 反射,动态加载
                Class person = Class.forName("Person");
                break;
            default:
        }
    }
}