public interface Person {
    void introduce();
}

public class Student implements Person {

    public Student() {
        // TODO Auto-generated constructor stub
    }

    public void introduce() {
        System.out.println("我要去听课");
    }

}

public class Teacher implements Person {

    public Teacher() {
        // TODO Auto-generated constructor stub
    }

    @Override
    public void introduce() {
        // TODO Auto-generated method stub
        System.out.println("我要去讲课");
    }

}

public class Introduce implements Person {

    Person person;

    public Introduce() {
        // TODO Auto-generated constructor stub
    }

    public Introduce(Person person) {
        this.person = person;
    }

    @Override
    public void introduce() {
        // TODO Auto-generated method stub
        System.out.println("大家好");
        person.introduce();
    }

}

public class Test {

    public Test() {
        // TODO Auto-generated constructor stub
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Student student = new Student();
        Introduce sIntroduce = new Introduce(student);
        sIntroduce.introduce();

        Teacher teacher = new Teacher();
        Introduce tIntroduce = new Introduce(teacher);
        tIntroduce.introduce();
    }

}

大家好
我要去听课
大家好
我要去讲课