Java返回值-类、抽象类、接口

目录

用 [TOC]来生成目录：

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返回值类型

返回值类型
    基本类型:(基本类型太简单，我不准备讲解)
    引用类型：
        类:返回的是该类的对象
        抽象类:返回的是该抽象类的子类对象
        接口:返回的是该接口的实现类的对象

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类名作为返回值-代码块

//  <1>类作为返回值
class Student {
    public void study() {
        System.out.println("Good Good Study,Day Day Up");
    }
}

class StudentDemo {
    public Student getStudent() {
        //Student s = new Student();
        //return s;
        return new Student();
    }
}

class StudentTest2 {
    public static void main(String[] args) {
        StudentDemo sd = new StudentDemo();
        Student s = sd.getStudent(); //new Student(); Student s = new Student();
        s.study();
    }
}

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抽象类作为返回值-代码块

//  <2> 抽象类作为返回值
abstract class Person {
    public abstract void study();
}

class PersonDemo {
    public Person getPerson() {
        //Person p = new Student();
        //return p;

        return new Student();
    }
}

class Student extends Person {
    public void study() {
        System.out.println("Good Good Study,Day Day Up");
    }
}

class PersonTest2 {
    public static void main(String[] args) {
        //需求：我要测试Person类中的study()方法
        PersonDemo pd = new PersonDemo();
        Person p = pd.getPerson(); //new Student();  Person p = new Student(); 多态
        p.study();
    }
}

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接口作为返回值-代码块

//  <3> 接口作为返回值
//定义一个说的的接口
interface speak{
    public abstract void speakeng();
}

class teacher implements speak{
    public void speakeng(){
        System.out.println("I can speak!");
    }
}

class teacherDemo{
    public speak show(){
        return  new teacher(); //返回的是该接口的实现类的对象
    }
}

public class TeacherTest4 {

    public static void main(String[] args) {
        teacherDemo td =new teacherDemo();
        speak l= td.show();  //new teacher();  speak l=new teacher();  多态
        l.speakeng();
    }
}