动态代理是基于什么原理（总结杨晓峰的博客）

public class MyDynamicProxy{
    public static void main(String[] args) {
        HelloImpl hello = new HelloImpl();
        MyInvocationHandler handler = new MyInvocationHandler(hello);
        //构造代码实例
        Hello proxyHello = (Hello)Proxy.newProxyInstance(HelloImpl.class.getClassLoader(),HelloImpl.class.getInterfaces(),handler);
        //调用代理方法
        proxyHello.sayHello();
    }

    interface Hello{
        void sayHello();
    }

    class HelloImpl implements Hello{
        @Override
        public void sayHello(){
            System.out.println("Hello world");
        }
    }

    class MyInvocationHandler implements MyInvocationHandler{
        private Object target;
        public MyInvocationHandler(Object target){
            this.target = target;
        }

        @Override
        public Object invoke(Object proxy,Method method,Object[] args) throws Throwable{
            System.out.println("Invoking sayHello");
            Object result = method.invoke(target,args);
            return result;
        }
    }
}