Java 访问数组中的数组内的元素

鉴于以下类别：

public class Customer {
    protected String firstName;
    protected String lastName;
    protected String ID;
    protected float  amountSpent;

    // Contructor
    // Accessors and mutators
}

public class Gold extends Customer {
    protected discount;

    // overloaded contructor
    // Accessors and mutator
}

和下面的代码

Customer[][] arr = new Customer[2][1];

Customer[] preferredArr = new Gold[3];
Customer[] regularArr = new Customer[3];

preferredArr[0] = new Gold("John", "Doe", "1234", 45, .12)
regularArr[0] = new Customer("Caroline", "Merritt", "5678", 60)

arr[0] = preferredArr;
arr[1] = regularArr;

---

如果John的信息位于

arr

数组中，如何使用

preferredArr[0].getFirstName（）

访问该信息。我也不能按照教授的要求使用ArrayList。谢谢你的帮助

preferredArr[0]。getFirstName（）

可以工作，因为对象位于preferredArr中。确切地说是对象的引用。

arr[0][0].getFirstName（）

：还有，工作，因为在

arr[0][0]

中只存储对同一对象的引用

class Customer {
    protected String firstName;
    protected String lastName;
    protected String ID;
    protected float  amountSpent;

    // Contructor
    Customer(String firstName, String lastName, String ID, float  amountSpent)
    {
        this.firstName = firstName;
        this.lastName = lastName;
        this.ID = ID;
        this.amountSpent = amountSpent;
    }
    
    // Accessors and mutators
    
    public String getFirstName()
    {
        return this.firstName;
    }
}

class Gold extends Customer {
    protected int discount;

    // overloaded contructor
    Gold(String firstName, String lastName, String ID, int discount, float  amountSpent)
    {
        super(firstName, lastName, ID, amountSpent);
        this.discount = discount;
    }
    // Accessors and mutator
}

public class Main
{
    public static void main(String[] args) 
    {
        
        Customer[][] arr = new Customer[2][1];

        Customer[] preferredArr = new Gold[3];
        Customer[] regularArr = new Customer[3];
        
        preferredArr[0] = new Gold("John", "Doe", "1234", 45, 0.12f);
        regularArr[0] = new Customer("Caroline", "Merritt", "5678", 60);
        
        arr[0] = preferredArr;
        arr[1] = regularArr;
        
        System.out.println("preferredArr[0].getFirstName() = "+preferredArr[0].getFirstName());
        
        System.out.println("arr[0][0].getFirstName() = "+arr[0][0].getFirstName());   

    }
}

结果是：

preferredArr[0].getFirstName() = John                                                           
arr[0][0].getFirstName() = John

您可以检查：。
和

---

祝你好运。

我建议你

arr[0][0]。getFirstName（）

但是你必须确保

preferedArr

在启动你的程序时会停留在索引0处。