Question

我目前正在研究Java并且到目前为止正在使用普通数组。下学期我们将使用像ArrayList等数据结构，但我决定提前阅读。我已经读过，为了存储不能重复的数据，集合是首选的数据结构，但在下面的代码中，用户仍然可以输入重复的条目？任何机构都可以向我解释这个过程，也许可以解决我的问题吗？

public class Lotto {

private static final int INPUT_SIZE = 6;

private static final int MIN_NUMBER_POSSIBLE = 0;

private static final int MAX_NUMBER_POSSIBLE = 25;

private Set<Integer> userNumbers = new HashSet<Integer>();

private Set<Integer> randomNumbers = new HashSet<Integer>();

public static void main(String[] args) {
    Lotto c = new Lotto();
    c.generateRandomNumbers();
    System.out.println("Pick " + INPUT_SIZE + " numbers from "
            + MIN_NUMBER_POSSIBLE + " to " + MAX_NUMBER_POSSIBLE + ".");
    c.readUserNumbers();
    if (c.doUserNumbersMatchRandomNumbers()) {
        System.out.println("You win :) !");
    } else {
        System.out.println("Sorry you failed :( !");
        c.showRandomNumbersToUser();
    }
}

private void generateRandomNumbers() {
    Random random = new Random();
    for (int i = 0; i < INPUT_SIZE; i++) {
        randomNumbers.add(random.nextInt(MAX_NUMBER_POSSIBLE));
    }
}

private void showRandomNumbersToUser() {
    System.out.println("\nRandom numbers where : ");
    for (Integer randomNumber : randomNumbers) {
        System.out.println(randomNumber + "\t");
    }
}

private void readUserNumbers() {
    Scanner input = new Scanner(System.in);
    int inputSize = 1;
    while (input.hasNextInt() && inputSize < INPUT_SIZE) {
        int numberChoosen = input.nextInt();
        if (numberChoosen < MIN_NUMBER_POSSIBLE
                || numberChoosen > MAX_NUMBER_POSSIBLE) {
            System.out.println("Your number must be in "
                    + MIN_NUMBER_POSSIBLE + " - " + MAX_NUMBER_POSSIBLE
                    + " range.");
        } else {
            userNumbers.add(numberChoosen);
            inputSize++;
        }
    }
}

private boolean doUserNumbersMatchRandomNumbers() {
    for (Integer userNumber : userNumbers) {
        if (!randomNumbers.contains(userNumber)) {
            return false;
        }
        printMatchingNumber(userNumber);
    }
    return true;
}

private void printMatchingNumber(int num) {
    System.out.println("Your number, " + num + ", has been called.");
}

}

Answer 1

成功添加对象后，

Set#add(Object)会返回true，否则会返回false。它不会抛出异常，因此您需要添加条件以检查操作是否成功：

if (userNumbers.add(numberChoosen)) {
    System.out.println("Number added successfully");
} else {
    System.out.println("Duplicate number detected");
}

Answer 2

设置不禁止多次输入唯一值。您可以检查前置条件，例如Set.add。

所以不要只是打电话：

userNumbers.add(numberChoosen);

试

if (!userNumbers.contains(numberChoosen)) {
    userNumbers.add(numberChoosen);
} else {
    // do stuff...
}

使用集时验证重复的用户条目

2 个答案: