多态的理解(二)

public abstract class Person {
    private String name;

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

    public abstract String getDescription();

    public String getName() {
        return name;
    }
}

public class Student extends Person {
    private String major;

    public Student(String name, String major) {
        super(name);
        this.major = major;
    }

    @Override
    public String getDescription() {
        return "a student majoring in" + major;
    }
}

Person[] people = new Person[2];
Person[0] = new Student(...);
System.out.println(people[0].getName() + "," + people[0].getDescription());

有人可能对 people[0].getDescription() 感到疑惑。请牢记，由于不能构造Person的对象，所以变量永远不会引用Person对象，而是引用具体子类对象，这些对象都定义了getDescription方法。同时，编译器也只允许调用在类中声明的方法。