面向对象之形式参数与返回值问题

1.形式参数为类名时：需要的是该类的对象
程序代码如下：

1: class Student {

2:     public void study() {

3:         System.out.println("Good Good Study,Day Day Up");

4:     }

5: }

6: 

7: class StudentDemo {

8:     public void method(Student s) { //ss; ss = new Student();  Student s = new Student();

9:         s.study();

10:     }

11: }

12: 

13: class StudentTest {

14:     public static void main(String[] args) {

15:         //需求：我要测试Student类的study()方法

16:         Student s = new Student();

17:         s.study();

18:         System.out.println("----------------");

19:

20:         //需求2：我要测试StudentDemo类中的method()方法

21:         StudentDemo sd = new StudentDemo();

22:         Student ss = new Student();

23:         sd.method(ss);

24:         System.out.println("----------------");

25:

26:         //匿名对象用法

27:         new StudentDemo().method(new Student());

28:     }

29: }

2.形式参数为抽象类时：需要的是该抽象的类子类对象

程序代码如下：

1: abstract class Person {

2:     public abstract void study();

3: }

4: 

5: class PersonDemo {

6:     public void method(Person p) {//p; p = new Student();  Person p = new Student(); //多态

7:         p.study();

8:     }

9: }

10: 

11: //定义一个具体的学生类

12: class Student extends Person {

13:     public void study() {

14:         System.out.println("Good Good Study,Day Day Up");

15:     }

16: }

17: 

18: class PersonTest {

19:     public static void main(String[] args) {

20:         //需求：我要使用PersonDemo类中的method()方法

21:         PersonDemo pd = new PersonDemo();

22:         Person p = new Student();

23:         pd.method(p);

24:     }

25: }

3.形式参数为接口名时：需要该接口的实现类对象

程序代码如下：

1: //定义一个爱好的接口

2: interface Love {

3:     public abstract void love();

4: }

5: 

6: class LoveDemo {

7:     public void method(Love l) { //l; l = new Teacher();  Love l = new Teacher(); 多态

8:         l.love();

9:     }

10: }

11: 

12: //定义具体类实现接口

13: class Teacher implements Love {

14:     public void love() {

15:         System.out.println("老师爱学生,爱Java,爱林青霞");

16:     }

17: }

18: 

19: class TeacherTest {

20:     public static void main(String[] args) {

21:         //需求：我要测试LoveDemo类中的love()方法

22:         LoveDemo ld = new LoveDemo();

23:         Love l = new Teacher();

24:         ld.method(l);

25:     }

26: }

4.返回值类型为类名时：返回的是该类的对象

程序代码如下：

1: class Student {

2:     public void study() {

3:         System.out.println("Good Good Study,Day Day Up");

4:     }

5: }

6: 

7: class StudentDemo {

8:     public Student getStudent() {

9:         //Student s = new Student();

10:         //Student ss = s;

11:

12:         //Student s = new Student();

13:         //return s;

14:         return new Student();

15:     }

16: }

17: 

18: class StudentTest2 {

19:     public static void main(String[] args) {

20:         //需求：我要使用Student类中的study()方法

21:         //但是，这一次我的要求是，不要直接创建Student的对象

22:         //让你使用StudentDemo帮你创建对象

23:         StudentDemo sd = new StudentDemo();

24:         Student s = sd.getStudent(); //new Student(); Student s = new Student();

25:s.study();

26:     }

27: }

5.返回值类型为抽象类名时：返回的是该类的子类对象

程序代码如下：

1: abstract class Person {

2:     public abstract void study();

3: }

4: 

5: class PersonDemo {

6:     public Person getPerson() {

7:         //Person p = new Student();

8:         //return p;

9:

10:         return new Student();

11:     }

12: }

13: 

14: class Student extends Person {

15:     public void study() {

16:         System.out.println("Good Good Study,Day Day Up");

17:     }

18: }

19: 

20: class PersonTest2 {

21:     public static void main(String[] args) {

22:         //需求：我要测试Person类中的study()方法

23:         PersonDemo pd = new PersonDemo();

24:         Person p = pd.getPerson(); //new Student();  Person p = new Student(); 多态

25:p.study();

26:     }

27: }

6.返回值类型为接口名时：返回的是该接口的实现类的对象

程序代码如下：

1: //定义一个爱好的接口

2: interface Love {

3:     public abstract void love();

4: }

5: 

6: class LoveDemo {

7:     public Love getLove() {

8:         //Love l = new Teacher();

9://return l;

10:

11:return new Teacher();

12:     }

13: }

14: 

15: //定义具体类实现接口

16: class Teacher implements Love {

17:     public void love() {

18:         System.out.println("老师爱学生,爱Java,爱林青霞");

19:     }

20: }

21: 

22: class TeacherTest2 {

23:     public static void main(String[] args) {

24:         //如何测试呢?

25:LoveDemo ld = new LoveDemo();

26:         Love l = ld.getLove(); //new Teacher(); Love l = new Teacher(); 多态

27:         l.love();

28:     }

29: }