Java引用类型作为形参和返回值

一、什么是引用类型

在Java中引用类型包括三种：类、抽象类、接口。

二、引用类型作为形参使用

1、类作为形参

/**
 * 类作为形参，实际传递的是该类的对象
 */
class Student {

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

class StudentDemo {

    public void show(Student s) {
        s.study();
    }
}

public class StudentTest {

    public static void main(String[] args) {

        StudentDemo sd = new StudentDemo();
        Student s = new Student();
        sd.show(s);
    }
}

2、抽象类作为形参

/**
 * 抽象类作为形参，传递的是实现该抽象类的子类对象
 */
abstract class Person {

    public abstract void eat();
}

class XiaoMing extends Person {

    @Override
    public void eat() {
        // TODO Auto-generated method stub
        System.out.println("小明爱吃米饭");
    }
}

class PersonDemo {

    public void show(Person p) {
        p.eat();
    }
}

public class PersonTest {

    public static void main(String[] args) {
        PersonDemo pd = new PersonDemo();
        // 方式一、传递的是实现该抽象类的子类对象
        Person p = new XiaoMing(); // 多态
        pd.show(p);
        System.out.println("------------------");
        // 方式二、直接实现抽象类，传递匿名子类对象
        pd.show(new Person() {

            @Override
            public void eat() {
                // TODO Auto-generated method stub
                System.out.println("小明爱上了吃面条");
            }
        });
    }
}

3、接口作为形参

/**
 * 接口作为形参，传递的是实现该接口的子类对象
 */
interface Teacher {
    // 接口 like a 的关系，并不是所有 Teacher 都抽烟
    public abstract void smoke();
}

class TeacherZhang implements Teacher {

    @Override
    public void smoke() {
        // TODO Auto-generated method stub
        System.out.println("老师爱抽中华");
    }
}

class TeacherDemo {

    public void show(Teacher t) {
        t.smoke();
    }
}

public class TeacherTest {

    public static void main(String[] args) {
        TeacherDemo td = new TeacherDemo();
        // 方式一、传递的是实现该接口的子类对象
        Teacher t = new TeacherZhang(); // 多态
        td.show(t);
        System.out.println("------------------");
        // 方式二、直接实现接口，传递匿名子类对象
        td.show(new Teacher() {

            @Override
            public void smoke() {
                // TODO Auto-generated method stub
                System.out.println("老师不抽中华了，爱上了雪茄");
            }
        });
    }
}

三、返回引用类型值

1、返回类类型值，实际返回的是该类的对象

/**
 * 类作为返回值，实际返回的是该类的对象
 */
class Student {

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

class StudentDemo {

    public Student getInstance() {
        return new Student();
    }
}

public class StudentTest2 {

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

2、返回抽象类类型值，实际返回的是实现该抽象类子类的对象

/**
 * 抽象类作为返回值，实际返回的是实现该抽象类的子类对象
 */
abstract class Person {

    public abstract void eat();
}

class XiaoMing extends Person {

    @Override
    public void eat() {
        // TODO Auto-generated method stub
        System.out.println("小明爱吃米饭");
    }
}

class PersonDemo {

    public Person getIntance() {
        return new XiaoMing();
    }
}

public class PersonTest2 {

    public static void main(String[] args) {
        PersonDemo pd = new PersonDemo();
        Person p = pd.getIntance();
        p.eat();
    }
}

3、返回接口类型值，实际返回的是实现该接口子类的对象

/**
 * 接口作为返回值，实际返回的是实现该接口的子类对象
 */
interface Teacher {
    // 接口 like a 的关系，并不是所有 Teacher 都抽烟
    public abstract void smoke();
}

class TeacherZhang implements Teacher {

    @Override
    public void smoke() {
        // TODO Auto-generated method stub
        System.out.println("老师爱抽中华");
    }
}

class TeacherDemo {

    public Teacher getIntance() {
        return new TeacherZhang();
    }
}

public class TeacherTest2 {
    public static void main(String[] args) {
        TeacherDemo td = new TeacherDemo();
        Teacher t = td.getIntance();
        t.smoke();
    }
}