这个方式也是一个构造方法，用一个Person对象创建新对象

构造方法，参数类型为Person
例：
Person p = new Person("name", true);
Person p0 = new Person(p);
.....

class Student{

private String name;
private String sex;
}

Person(Student student){
this.name = student.name;
this.sex = student.sex;
};

Person(Person p) {
this.name = p.name;
this.sex = p.sex;
}