public class Test5 {
public static void main(String []args)throws Exception{       
Class<myClass> clazz=myClass.class;
Method method = clazz.getMethod("speak", String.class);
method.invoke(clazz.newInstance(),"Hello world!!!");
}
}
class myClass{
        public void speak(String str)
        {System.out.println(str);
        }
}

public class Test5 {
public static void main(String []args)throws Exception{        
Class<myClass> clazz=myClass.class;//获取你想得到类
Method method = clazz.getMethod("speak", String.class);//类里的speak方法，参数是String类型
method.invoke(clazz.newInstance(),"Hello world!!!");//clazz.newInstance是实例化你得到的类，然后传入Hello world给speak方法，然后调用
}
}
class myClass{
        public void speak(String str)
        {System.out.println(str);
        }
}