// 通过“实例”获取类

String str = "hello";

Class cls1 = str.getClass();

// 通过“类型”获取类

Class cls2 = String.class;

// 通过“全路径字符串”获取类

Class cls3 = Class.forName("java.lang.String");

cls1.getName(); //"java.lang.String"

cls1.getSimpleName(); //"String"

cls1.getPackage().getName(); //"java.lang"

class Person {

    public void say() {

        System.out.println("Person");

    }

}

class Student extends Person {

    @Override

    public void say() {

        System.out.println("Student");

    }

}

public static void main(String[] args) {

    Person p1 = new Person();

    Person p2 = new Student();

    p1.say(); // "Person"

    p2.say(); // "Student"

}