对象作为返回值类型&&链式编程

package com.imooc;
class Student{
    public void study(){
        System.out.println("学生学习");
    }
}
class StudentDemo{
    public Student getStudent(){
        return new Student();
    }
}
public class ReturnDemo {
    public static void main(String[] args){
        StudentDemo sd = new StudentDemo();
        Student s = sd.getStudent();
        s.study();
    }
}

抽象类作为返回值类型，返回的是该抽象类的子类对象

package com.imooc;
abstract class Person{
    public abstract void study();
}
class Student extends Person{
    public void study(){
        System.out.println("学生爱学习");
    }
}
class StudentDemo{
    public Person getPerson(){
        return new Student();
    }
}
public class ReturnDemo {
    public static void main(String[] args){
        StudentDemo sd = new StudentDemo();
        Person p = sd.getPerson();
        p.study();
    }
}

接口作为返回返回值类型，返回的是实现该接口的实现类的对象

package com.imooc;
interface Love{
    public abstract void love();
}
class Teacher implements Love{
    public void love(){
        System.out.println("老师爱上课");
    }
}
class TeacherDemo{
    public Love getLove(){
        return new Teacher(); //因为teacher实现了Love接口
    }
}
public class TeacherTest {
    public static void main(String[] args){
        TeacherDemo td = new TeacherDemo();
        Love l = td.getLove();
        l.love();
    }
}

如果每次调用完方法都返回一个对象，那么便可以实现链式编程

例如：

package com.imooc;
interface Love{
    public abstract void love();
}
class Teacher implements Love{
    public void love(){
        System.out.println("老师爱上课");
    }
}
class TeacherDemo{
    public Love getLove(){
        return new Teacher(); //因为teacher实现了Love接口
    }
}
public class TeacherTest {
    public static void main(String[] args){
        TeacherDemo td = new TeacherDemo();
        Love l = td.getLove();
        l.love();

        //链式编程：每次调用完方法之后返回的是一个对象
        td.getLove().love();
        //td是一个对象，td.getLovce()返回的是一个实现Love接口的对象，
        //可以再调用这个对象的方法
    }
}