java - 引用引用数组的方法？

Question

我错过了一次 Java 讲座，主题是类、方法、构造函数等。家庭作业是一项任务:

Create a class Person, objects of which describe persons, and which contains only two felds: name (String) and year of birth (int). In this class, define

• constructor taking name and year of birth;

• constructor taking only name and setting the year of birth to default value 1990;

• method isFemale returning true if this person is a woman (we assume, not very sensibly, that only women and all women have names ending with the letter 'a'); otherwise the method returns false;

• static function getOlder taking two references to objects of class Person and returning the reference to the older of these two persons;

• static function getOldest taking the reference to an array of references to objects of class Person and returning the reference to the oldest person represented in the array;

• static function getYoungestFemale taking the reference to an array of refe- rences to objects of class Person and returning the reference to the youngest woman represented in the array, or null if there is no woman in the array.

In a separate class, write a main function in which the whole functionality of the class Person is tested.

我查看了一些教程和解释，我没有直接去这里寻求帮助，但是在 2 个小时的扯掉我的头发之后我只能想出这个:

public class Person {
    String name;
    int yob; //year of birth

    public Person() {
        Person jan = new Person("Jan", 1995); //the names are polish
        Person joanna = new Person("Joanna", 1993);
        Person michal = new Person("Michal", 1980);
        Person beata = new Person("Beata", 1979);
        Person kazimierz = new Person("Kazimierz", 1998);
        Person magdalena = new Person("Magdalena", 1999);
    }

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

    public Person(String name) {
        this.name = name;
        this.yob = 1990;
    }

    public static boolean isFemale(String name) {
        if(name.equals("Joanna")) {
            return true;
        } else {
            return false;
        }
    }

    public static String getOlder(Person x?, Person y?) { // if I understand the task correctly, I should reference any two names?
        if(x?.yob>y?.yob) {
            return x?.name;
        } else {
            return y?.name;
        }

    //getOldest and getYoungestFemale methods go here

    }
}

但是，我无法理解最后三个步骤。我的大脑真的在沸腾。如果有人能解释最后三个要点(getOlder 引用任何 2 人和 getOldest/getYoungestFemale)，那将非常有帮助

如果你没有时间解释，一些“引用数组的方法”的例子应该足以让我有一个基本的理解。

提前致谢。

Answer 1

通常.. 你不会称它为“对某事物的引用数组的引用”你只是说“某事物的数组”。尽管对象数组是对象引用数组。就像对象的变量只是对对象的引用。

Type heyImAReference = new ImTheObject();

所以当你写

Person person = new Person();

您将拥有类 Person 作为类型，person 作为对该类实例(或对象)的引用以及 new Person() 的结果实体作为被引用的实际事物。通常称为“实例”或在您的情况下称为“对象”。

当涉及到人的排列时，你会这样做

Person[] persons = new Person[5];

你通过 new Person[5] 创建一个有 5 个槽的数组实例，在每个槽中可以形象地去一个 Person 实例，实际上虽然你有 5 个引用。 Person[0] 是第一个，Person[1] 是第二个，依此类推。所以这是一个“对 Person 类对象的引用数组”。

persons 是对此的引用。所以它是“对 Person 类对象的引用数组的引用”

• static 函数 getOldest 获取对 Person 类对象的引用数组的引用，并返回对数组中表示的最老人物的引用

无非就是

static Person getOldest(Person[] persons) {
    ...
}

我会称该方法为接受一组 Person 并返回一个 Person 的方法。尽管从技术上讲，这只是进出的引用。 Person 对象不会“移动”