将 ArrayList<Object> 转换为字符串

Question

嗨，我正在尝试练习 java，而且才刚刚开始！为了练习，我正在尝试构建一个简单的扑克游戏，但遇到了纸牌数组列表问题。我试图打印出来，但只有地址输出到控制台，自然我尝试使用 .toString 方法并创建我自己的 toString 方法来尝试检查数组列表是否输入正确。下面是我的 Card class 和 Arraylist{Card}Deck。下面是我的代码

package poker;

import java.util.ArrayList;

public class Card {
    private String _suit;
    private int _cardNum;

    public Card(int cardNum, String suit) {
        _suit = suit;
        _cardNum = cardNum;
    }
    public String toString() {
        return _suit +_cardNum;
    }

    static ArrayList<`enter code here`Card> Deck = new ArrayList<Card>() {{
        add(new Card(0,"Hearts"));
        add(new Card(1,"Hearts"));
        add(new Card(1,"Hearts"));
        add(new Card(2,"Hearts"));
        add(new Card(3,"Hearts"));
        add(new Card(4,"Hearts"));
        add(new Card(5,"Hearts"));
        add(new Card(6,"Hearts"));
        add(new Card(7,"Hearts"));
        add(new Card(8,"Hearts"));
        add(new Card(9,"Hearts"));
        add(new Card(10,"Hearts"));
        add(new Card(11,"Hearts"));
        add(new Card(12,"Hearts"));
        add(new Card(13,"Hearts"));
        add(new Card(0,"Spades"));
        add(new Card(1,"Spades"));
        add(new Card(2,"Spades"));
        add(new Card(3,"Spades"));
        add(new Card(4,"Spades"));
        add(new Card(5,"Spades"));
        add(new Card(6,"Spades"));
        add(new Card(7,"Spades"));
        add(new Card(8,"Spades"));
        add(new Card(9,"Spades"));
        add(new Card(10,"Spades"));
        add(new Card(11,"Spades"));
        add(new Card(12,"Spades"));
        add(new Card(13,"Spades"));
        add(new Card(0,"Clubs"));
        add(new Card(1,"Clubs"));
        add(new Card(2,"Clubs"));
        add(new Card(3,"Clubs"));
        add(new Card(4,"Clubs"));
        add(new Card(5,"Clubs"));
        add(new Card(6,"Clubs"));
        add(new Card(7,"Clubs"));
        add(new Card(8,"Clubs"));
        add(new Card(9,"Clubs"));
        add(new Card(10,"Clubs"));
        add(new Card(11,"Clubs"));
        add(new Card(12,"Clubs"));
        add(new Card(13,"Clubs"));
        add(new Card(0,"Diamonds"));
        add(new Card(1,"Diamonds"));
        add(new Card(2,"Diamonds"));
        add(new Card(3,"Diamonds"));
        add(new Card(4,"Diamonds"));
        add(new Card(5,"Diamonds"));
        add(new Card(6,"Diamonds"));
        add(new Card(7,"Diamonds"));
        add(new Card(8,"Diamonds"));
        add(new Card(9,"Diamonds"));
        add(new Card(10,"Diamonds"));
        add(new Card(11,"Diamonds"));
        add(new Card(12,"Diamonds"));
        add(new Card(13,"Diamonds"));
    }};
}

和我的 MainApp

package poker;

import java.util.Random;
import static java.lang.System.out;

public class MainApp {

    public static void main(String[] args) {
        for(int i = 0;i <Card.Deck.size();i++) {
            out.println(Card.toString());

        }
    }
}

在打印行中出现了我的问题。如何将数组列表从 class 类型转换为字符串输出？提前致谢！

Answer 1

由于 toString() 不是静态方法，您需要在 class 的实例上调用它。因此，将 MainApp 中的行 out.println(Card.toString()); 更改为 out.println(Card.Deck.get(i).toString());。

附带说明一下，我注意到您每套花色有 14 张牌，我认为这是无意的。

Answer 2

你能试试下面的方法吗？它应该会打印 ArrayList 的所有字符串内容。

System.out.println(Card.Deck);

类似

[Hearts0, Hearts1, Hearts1, Hearts2, Hearts3, Hearts4, Hearts5, Hearts6, Hearts7, Hearts8, Hearts9, Hearts10, Hearts11, Hearts12, Hearts13, Spades0, Spades1, Spades2, Spades3, Spades4, Spades5, Spades6, Spades7, Spades8, Spades9, Spades10, Spades11, Spades12, Spades13, Clubs0, Clubs1, Clubs2, Clubs3, Clubs4, Clubs5, Clubs6, Clubs7, Clubs8, Clubs9, Clubs10, Clubs11, Clubs12, Clubs13, Diamonds0, Diamonds1, Diamonds2, Diamonds3, Diamonds4, Diamonds5, Diamonds6, Diamonds7, Diamonds8, Diamonds9, Diamonds10, Diamonds11, Diamonds12, Diamonds13]

Answer 3

您看到的错误是什么？

我看到的最大问题是您的 for 循环没有使用索引来取消引用 Deck 数组的成员：

for(int i = 0;i <Card.Deck.size();i++) {
            out.println(Card.toString());

        }

卡片是 class - 不是对象。您已经创建了一堆 Card class 对象，但这不是您在该代码中引用的对象。要引用对象实例而不是 class，请执行以下操作：你应该更换 Card.toString() 和： Card.Deck.get(i).toString() -- 但有更好的方法，请参见下文。

顺便说一句，您可能应该使用@Override 属性来实现toString。它可能不是绝对必要的，但清楚地表明您正在覆盖默认实现：

    @Override
    public String toString() {
        return _suit +_cardNum;
    }

正如我上面提到的，有一种更简单的方法可以打印牌组中的每张卡片：使用迭代器快捷方式 for 而不是尝试将数组列表视为数组：

    public void printDeck() {
        for(Card card : Card.Deck) {
            out.print(card.toString());
        }
    }

Answer 4

您的 Card.toString() 没有引用 Card in Deck 对象。您要做的是从 Deck 对象打印 Card 的字符串值。如果你使用的是Java 8，你可以使用下面的代码：

Card.Deck.forEach(card -> System.out.println(card.toString()));

将 ArrayList<Object> 转换为字符串

Convert ArrayList<Object> to string

java

arraylist

tostring