我已經(jīng)嘗試過不使用類使用局部變量相同的問題。GUI應(yīng)該打開，我可以提交我想要的牌的數(shù)量，并將從一副牌中隨機(jī)選擇。和 GUI 上的其他按鈕也public class MainGUI extends Application { public void start(Stage primaryStage) { class deck { public ArrayList <Integer> Deck; public ArrayList<Integer> shuffleDeck(ArrayList<Integer> Deck) { int x = 52; for (int i = 1; i <= x; ++i ) { Deck.add(i); } Collections.shuffle(Deck); return Deck; } public ArrayList<Integer> randomCardsSelector(int x, ArrayList<Integer> Deck){ ArrayList<Integer> selectedCards = new ArrayList<Integer>(); Random rand = new Random(); for(int i = 1; i <= x; ++i) { int newElement = rand.nextInt(Deck.size()); selectedCards.add(Deck.get(newElement)); Deck.remove(newElement); } return selectedCards; } } //Horizontal box containing Label, TextField, Button, Cards drawn HBox topContainer = new HBox(); topContainer.setSpacing(10); topContainer.setPadding(new Insets(25,50,25,50)); //This is the label Label insertNbr = new Label(); insertNbr.setText("Number of cards:"); insertNbr.setPadding(new Insets(5,5,5,5)); //This the TextField TextField cardNbr = new TextField(); cardNbr.setPadding(new Insets(5,5,5,5)); cardNbr.setPrefWidth(30); //This is the submit button Button submitBtn = new Button(); submitBtn.setPadding(new Insets(5,5,5,5)); submitBtn.setText("Submit"); HBox newBox = new HBox(); //This is the fetch button Button fetchBtn = new Button(); fetchBtn.setPadding(new Insets(5,5,5,5)); fetchBtn.setText("Fetch"); fetchBtn.setDisable(true); });我已經(jīng)嘗試過不使用類使用局部變量相同的問題。
1 回答
冉冉說
TA貢獻(xiàn)1877條經(jīng)驗(yàn) 獲得超1個(gè)贊
您的代碼至少有兩個(gè)問題：
在方法中定義類
空點(diǎn)器異常
您在方法中定義了類：deckstart()
public class MainGUI extends Application {
public void start(Stage primaryStage) {
class deck {
}
}
}
這是行不通的。移動(dòng)類的外部：class deckMainGUI
public class MainGUI extends Application {
public void start(Stage primaryStage) {
}
}
class deck {
}
空點(diǎn)器異常
從堆棧跟蹤中：
Caused by: java.lang.NullPointerException
at MainGUI$1deck.shuffleDeck(MainGUI.java:36)
這涉及以下方法：
public ArrayList<Integer> shuffleDeck(ArrayList<Integer> Deck) {
int x = 52;
for (int i = 1; i <= x; ++i) {
Deck.add(i);
}
Collections.shuffle(Deck);
return Deck;
}
唯一可以在這里（因此導(dǎo)致異常）的實(shí)數(shù)變量是變量。所以讓舒爾它不是。nullDecknull
在您的代碼中，它是 null，因?yàn)槟鷦?chuàng)建了一個(gè)新實(shí)例并期望設(shè)置類成員，但它實(shí)際上是 。deckDecknull
看：
deck firstDeck = new deck();
firstDeck.Deck = firstDeck.shuffleDeck(firstDeck.Deck);
這里將是.解決此問題的一種方法是在創(chuàng)建新實(shí)例時(shí)立即初始化類成員：firstDeck.DecknullDeckdeck
class deck {
public ArrayList<Integer> Deck = new ArrayList<>();
}
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