1. 多态数组

• 数组的定义类型为父类类型，里面保存的实际元素类型为子类类型

• 应用实例：现有一个继承结构如下：要求创建 1 个 Person 对象、2 个 Student 对象和 2 个 Teacher 对象, 统一放在数组中，并调用每个对象say方法。
  

public class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String say(){
        return name + "\t" + age;
    }
}

public class Student extends Person {
    private double score;

    public Student(String name, int age, double score) {
        super(name, age);
        this.score = score;
    }

    public double getScore() {
        return score;
    }

    public void setScore(double score) {
        this.score = score;
    }
    //重写父类say方法
    @Override
    public String say() {
        return super.say() + " score=" + score;
    }
}

public class Teacher extends Person {
    private double salary;

    public Teacher(String name, int age, double salary) {
        super(name, age);
        this.salary = salary;
    }

    public double getSalary() {
        return salary;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }
    //重写父类 say 方法
    @Override
    public String say() {
        return super.say() + " salary=" + salary;
    }
}

public class PloyArray {
    public static void main(String[] args) {
        Person[] person = new Person[5];
        person[0] = new Person("jack", 20);
        person[1] = new Student("mike", 21, 90);
        person[2] = new Student("smith", 18, 100);
        person[3] = new Teacher("scott", 30, 20000);
        person[4] = new Teacher("king", 50, 30000);

        //循环遍历多态数组，调用 say() 方法
        for (int i = 0; i < person.length; i++) {
            //提示：Person[i]编译类型是 person,运行类型是根据实际情况JVM来判断
            System.out.println(person[i].say()); //动态绑定机制
        }
    }
}

• 应用实例升级：如何调用子类特有的方法，比如：Teacher 有一个 teach()方法， Student 有一个 study() 方法，怎么调用？

public class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String say(){
        return name + "\t" + age;
    }
}

public class Student extends Person {
    private double score;

    public Student(String name, int age, double score) {
        super(name, age);
        this.score = score;
    }

    public double getScore() {
        return score;
    }

    public void setScore(double score) {
        this.score = score;
    }
    //重写父类say方法
    @Override
    public String say() {
        return super.say() + " score=" + score;
    }
    //特有方法
    public void study(){
        System.out.println("学生 " + getName() + " 正在学Java课程");
    }
}

public class Teacher extends Person {
    private double salary;

    public Teacher(String name, int age, double salary) {
        super(name, age);
        this.salary = salary;
    }

    public double getSalary() {
        return salary;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }
    //重写父类 say 方法
    @Override
    public String say() {
        return super.say() + " salary=" + salary;
    }
    //特有方法
    public void teach(){
        System.out.println("老师 " + getName() + " 正在讲Java课程");
    }
}

public class PloyArray {
    public static void main(String[] args) {
        Person[] person = new Person[5];
        person[0] = new Person("jack", 20);
        person[1] = new Student("mike", 21, 90);
        person[2] = new Student("smith", 18, 100);
        person[3] = new Teacher("scott", 30, 20000);
        person[4] = new Teacher("king", 50, 30000);

        //循环遍历多态数组，调用 say() 方法
        for (int i = 0; i < person.length; i++) {
            //提示：Person[i]编译类型是 person,运行类型是根据实际情况JVM来判断
            System.out.println(person[i].say()); //动态绑定机制
            //使用类型判断 + 向下转型
            if (person[i] instanceof Student){//判断 person[i]运行类型是不是Student
                Student student = (Student) person[i];//向下转型
                student.study();
                //也可以使用  (Student) person[i].study();
            }else if (person[i] instanceof Teacher) {
                Teacher teacher = (Teacher) person[i];
                teacher.teach();

            }else if (person[i] instanceof Person){

            }else{
                System.out.println("你的类型有误，请自行检查");
            }
        }


    }
}