java - 收到未声明类和重复类的编译器错误

Question

我刚刚创建了一个程序，它创建一个卡片对象数组，对它们进行洗牌，然后打印它们。但我遇到了以下错误，作为一名学生，我很难理解为什么。

错误:

"HW6GetBig.java:23: error: class Card is public, should be declared in a file named Card.java public class Card {"

"HW6GetBig.java:39: error: class DeckOfCards is public, should be declared in a file named DeckOfCards.java public class DeckOfCards {"

"HW6GetBig.java:11: error: cannot find symbol DeckOfCards myDeckofCards = new DeckofCards();"

到目前为止，我很困惑，不知道为什么该类会以未声明的形式出现。如果我将文件名更改为 netbeans 中的 Card，我仍然收到错误消息，指出已找到重复的类。请帮忙。

非常感谢， - 协同作用

 class HW6GetBig
    {
        public static void main(String[] args)
        {
            DeckOfCards myDeckofCards = new DeckofCards();
            myDeckofCards.deckShuffler(); // Randomizes / Shuffles the Cards in the Deck, using a Random # and Swaps

            // Print 52 Cards in the Order in which they are dealt
            for (int i = 0; i < 13; i++) {
                // Deal and Print 4 Cards
                System.out.printf("%-20s%-20s%-20s%-20s\n",
                myDeckofCards.dealCard(), myDeckofCards.dealCard(),
                myDeckofCards.dealCard(), myDeckofCards.dealCard());
            }
        }
    }
    public class Card {
        //Card Class represents a Virtual Playing Card in our Deck
        private String rank; // Ranks Of Card
        private String suit; // Suit Of Card

        // Two Argument Constructor initializes card's face and suit
        public Card(String cardRank, String cardSuit) {
            rank = cardRank; // Intializing Values of Card's Rank
            suit = cardSuit; // Intializing Values of Card's Suit
        }
        // Return String representing the Card
        public String CardToString() {
            return rank + " of " + suit;
        }

    }
    public class DeckOfCards {
        private Card deck[]; //Declaration of Array of Card Objects
        private int topCard; //Card to be Dealt
        private final int NUM_CARDS = 52; // Constant # Of Cards in a Standard Deck
        int random = (int)(Math.random()*52+1);

        public DeckOfCards() {
            String ranks[] = {"Ace","Two","Three","Four","Five","Six","Seven",
            "Eight","Nine","Ten","Jack","Queen","King"};
            String suits[] = {"Spades","Hearts","Clubs","Diamonds"};

            deck = new Card[NUM_CARDS]; // Creating an Array of Card Objects
            topCard = 0; // Setting Current Card so 1st Card is deck[0]
            // Filling the Seats of our Empty Deck Room with Card Objects
            for (int i = 0; i < deck.length; i++) {
                deck[i] = new Card(ranks[i % 13], suits[i / 13]);
                // End of Deck Of Cards Constructor
            }
        }
            public void deckShuffler() {
                // After Shuffling, The Deck should begin at deck[0] once again
                topCard = 0;
                // For each Card, pick a "Random Card/#" and Swap.
                for(int i = 0; i < deck.length; i++) {
                    // Obtaining a Random # Between 0 and 51.
                    int j = random;
                    // Swapping Currently Selected Card (i) with Random Card (j)
                    Card tempObject = deck[i];
                    deck[i] = deck[j];
                    deck[j] = tempObject;
                }
            }
                public Card dealCard() {
                    // Ensure the Top Card does not exceed the Deck Length
                    if (topCard < deck.length) {
                    return deck[topCard++];
                    } else {
                    return null;
                    }
                }
            }

Answer 1

错误消息说明了一切:

class Card is public, should be declared in a file named Card.java
class DeckOfCards is public, should be declared in a file named DeckOfCards.java

以下是您的选择:

• 按照错误消息中的建议，将这两个类移至其自己的文件中。
• 从类声明中删除 public 修饰符。

请参阅 Java 语言规范中的相关部分，7.6. Top Level Type Declarations :

If and only if packages are stored in a file system (§7.2), the host system may choose to enforce the restriction that it is a compile-time error if a type is not found in a file under a name composed of the type name plus an extension (such as .java or .jav) if either of the following is true:

• The type is referred to by code in other compilation units of the package in which the type is declared.

• The type is declared public (and therefore is potentially accessible from code in other packages).