返回值是类，是抽象类，是接口的调用方法

返回值是类，是抽象类，是接口的调用方法
类：需要的是该类的对象
抽象类：返回值是该抽象类的子类
接口：返回的是该接口的实现子类

//返回值是类时
package Practie;
class Student{
	public void study() {
		System.out.println("好好学习");
	}
}
class StudentDemo{
	public Student getStudent() {
		return new Student();
	}
}
public class StudentTest {
	public static void main(String[] args) {
   StudentDemo sd = new StudentDemo();
   Student s =sd.getStudent();
   s.study();
	}
}

//返回值是抽象类时
package Practie;
abstract class Person{
	abstract public void study();
}
class PersonDemo{
	public Person getPerson(){
	return new Student();
	}
}
class Student extends Person{
	public void study() {
		System.out.println("好好学习");
	}
}
public class PersonTest {
public static void main(String[] args) {
	PersonDemo pd = new PersonDemo();
	Person p = pd.getPerson();
	p.study();
}
}

返回值是接口的时候
package Practie;
interface Person{
   abstract public void study();
}
class PersonDemo{
   public Person getPerson(){
   return new Student();
   }
}
class Student implements Person{
   public void study() {
   	System.out.println("好好学习");
   }
}
public class PersonTest {
public static void main(String[] args) {
   PersonDemo pd = new PersonDemo();
   Person p = pd.getPerson();
   p.study();
}
}