Java - 循环遍历ArrayList以扫描匹配值

Question

这个问题已经有答案了:

Iterating through a Collection, avoiding ConcurrentModificationException when removing objects in a loop (31 个回答)

已关闭 6 年前。

我正在尝试使用 ArrayList 编写一个简单的程序，用于添加值、删除值和打印值。但是，我在删除用户输入的值时遇到问题。用户应该输入指定数量的值(由用户确定)，然后程序应该删除这些值(如果有重复项，那么它应该只删除该数字的第一个实例，这很好)。它不会删除这些值，并且在某些情况下会删除一个值。我对我的代码有问题的地方有点困惑。这是我的删除值的代码:

private static void removeVals() {
        System.out.println("How many values would you like to remove?");
        int amountToRemove = scanner.nextInt();
        scanner.nextLine();
        System.out.println("Enter " + amountToRemove + " values:");
        for(int i = 0; i < amountToRemove; i++) {
            int vals = scanner.nextInt();
            if(arrayList.get(i).equals(vals)) {
                arrayList.remove(i);
            }
        }
        System.out.println("Values removed");
    }

这是我的完整代码:

public class Main {

    private static ArrayList<Integer> arrayList = new ArrayList<Integer>();
    private static Scanner scanner = new Scanner(System.in);

    public static void main(String[] args) {
        printOptions();

        int option = scanner.nextInt();
        while (option != 0) {
            switch(option) {
                case 1:
                    addVals();
                    printOptions();
                    option = scanner.nextInt();
                    break;
                case 2:
                    removeVals();
                    printOptions();
                    option = scanner.nextInt();
                    break;
                case 3:
                    printVals();
                    printOptions();
                    option = scanner.nextInt();
                    break;
                case 4:
                    printOptions();
                    printOptions();
                    option = scanner.nextInt();
                    break;
                default:
                    System.out.println("Not a valid option, please enter again:");
                    option = scanner.nextInt();
                    break;
            }
        }
    }

    private static void addVals() {
        System.out.println("How many values would you like to add?");
        int amountToAdd = scanner.nextInt();
        scanner.nextLine();
        System.out.println("Enter " + amountToAdd + " values:");
        for(int i = 0; i < amountToAdd; i++) {
            int vals = scanner.nextInt();
            arrayList.add(vals);
        }
    }

    private static void removeVals() {
        System.out.println("How many values would you like to remove?");
        int amountToRemove = scanner.nextInt();
        scanner.nextLine();
        System.out.println("Enter " + amountToRemove + " values:");
        for(int i = 0; i < amountToRemove; i++) {
            int vals = scanner.nextInt();
            if(arrayList.get(i).equals(vals)) {
                arrayList.remove(i);
            }
        }
        System.out.println("Values removed");
    }

    private static void printVals() {
        for(int i = 0; i < arrayList.size(); i++) {
            System.out.print(arrayList.get(i) + " ");
        }
        System.out.println();
    }

    private static void printOptions() {
        System.out.println();
        System.out.println("Program options: ");
        System.out.println("1. Add values\n2. Remove values\n3. Print values\n4. Print options\n0. Exit\n");
        System.out.println("\nWhat would you like to do? (enter an option):");
    }
}

Answer 1

arrayList.remove(i) 删除此列表中指定位置的元素。将所有后续元素向左移动(从索引中减去 1)。这是你的代码的错误有关更多详细信息，请参阅下面的链接 https://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html#remove(int) ,