ArrayList 是空的，但是为什么呢？
我正在尝试将卡片添加到 ArrayList 甲板上，但它似乎不起作用（大部分代码是 oracle.com 上的示例）。我可能正在做一些非常愚蠢的事情，但我似乎找不到它..这是代码：
public class Card {
public enum Rank
{
DEUCE, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT, NINE,
TEN, JACK, QUEEN, KING, ACE
}
public enum Suit
{
HEARTS, DIAMONDS, SPADES, CLUBS
}
private final Rank rank;
private final Suit suit;
private static final List<Card> deck = new ArrayList<Card>();
public Card(Rank rank, Suit suit)
{
this.suit = suit;
this.rank = rank;
}
// initializes deck
public void initDeck()
{
for (Suit suit : Suit.values())
{
for (Rank rank : Rank.values())
{
deck.add(new Card(rank, suit));
}
}
}
// returns a copy of the deck
public static ArrayList<Card> newDeck()
{
return new ArrayList<Card>(deck);
}
public Rank getRank()
{
return rank;
}
public Suit getSuit()
{
return suit;
}
public String toString()
{
return rank +" of "+ suit;
}
public static void main(String[] args)
{
System.out.println(deck.toString());
}
}
I'm trying to add Cards to ArrayList deck, but it doesn't seem to work(most of the code is an example on oracle.com ). I'm probably doing something really stupid, but I can't seem to find it.. this is the code:
public class Card {
public enum Rank
{
DEUCE, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT, NINE,
TEN, JACK, QUEEN, KING, ACE
}
public enum Suit
{
HEARTS, DIAMONDS, SPADES, CLUBS
}
private final Rank rank;
private final Suit suit;
private static final List<Card> deck = new ArrayList<Card>();
public Card(Rank rank, Suit suit)
{
this.suit = suit;
this.rank = rank;
}
// initializes deck
public void initDeck()
{
for (Suit suit : Suit.values())
{
for (Rank rank : Rank.values())
{
deck.add(new Card(rank, suit));
}
}
}
// returns a copy of the deck
public static ArrayList<Card> newDeck()
{
return new ArrayList<Card>(deck);
}
public Rank getRank()
{
return rank;
}
public Suit getSuit()
{
return suit;
}
public String toString()
{
return rank +" of "+ suit;
}
public static void main(String[] args)
{
System.out.println(deck.toString());
}
}
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评论（5）
很简单，在您的
main方法中，您只是一个toString()一个空的ArrayList。您根本没有在main方法中调用initDeck()方法。当您运行程序时
private static Final List; Deck = new ArrayList();
，牌组被分配了一个空的ArrayList。It's simple, in your
mainmethod, you're justtoString()an emptyArrayList. You haven't calledinitDeck()method in yourmainmethod at all.When you ran your program
private static final List<Card> deck = new ArrayList<Card>();
, deck was assigned an emptyArrayList.非常可疑的是，您的甲板是私有静态最终的，而您的 init 方法是公共的并且是非静态的。它可以初始化多次并包含比您预期更多的卡片。您可能想在静态块中进行初始化。
我将替换代码如下：
public static final且不可修改（通过集合）initDeckit is very suspicious that your
deckisprivate static finaland your init methodpublicandnon-static. It can be initialized several times and contain more cards then you would expect. You may want to do the initialization in static block instead.I would replace the code as follows:
public static finaland unmodifiable (via Collections)initDeckcompletely这是因为
initDeck()没有在任何地方被调用。尝试将public void initDeck()替换为static。It's because
initDeck()isn't called anywhere. Try to replacepublic void initDeck()withstatic.List定义中的关键字final用于具有无法更改的起始值的对象。请在此处查看
The keyword
finalin youList<card>definition is for object that will have an starting value that cannot be changed.Check it here
您的问题是您从未真正调用 initDeck，因此牌组保持为空，就像静态初始化程序运行时一样：
其他问题：
initDeck()是一个实例方法，但deck 是静态引用。initDeck()是 Card 上的一个方法。deck是Card的静态成员，但卡不拥有或定义牌组。newDeck是毫无意义的。简而言之，您的设计一团糟 - 您需要更多、更努力地思考实体及其相互关系。
Your problem is that you never actually invoke initDeck, so the deck remains empty, as it was when the static initializer ran:
Other problems:
initDeck()is an instance method, butdeckis a static reference.initDeck()is a method on Card.deckis a static member ofCard, but a card does not own or define a deck.newDeckis nonsensical in the face of a static final deck.In short, your design is messed up - you need to think more and harder about the entities and their inter-relationships.