Java - 基数排序 不兼容的类型？

Question

对于我的类(class)，我们必须为基数排序算法编写 Java 代码。我了解该算法，并且我认为我已经找到了解决方案，但我的代码中出现了不兼容的类型错误，而且我不明白为什么。

    import java.util.*;

    public class RadixSort {

        public static void radixSort(int[] list) {

        // will be passed to getKey to decide what to divide the number by before %10
        int div = 1;

        // repeat once for the max number of digits of the numbers
        for (int i = 0; i < 3; i++) {
            ArrayList bucket[] = new ArrayList[19];

            // distribute the elements from the list to the buckets
            for (int j = 0; j < list.length-1; j++) {
                int key = getKey(list[j], div);

                // add 9 so that if key is negative, it will now be 0 or positive so an out of bounds exception isn't thrown
                // so bucket[0] means the key was -9, and bucket[18] means the key was 9
                if (bucket[key+9] == null)
                    bucket[key+9] = new ArrayList();
                bucket[key+9].add(list[j]);
            }

            // move the elements from the buckets back to list
            int z = 0;
            for (int x = 0; x < 19; x++) {
                if (bucket[x] != null) {
                    for (int y: bucket[x]) {  // incompatible types???
                        list[z] = y;
                        z++;
                    }
                }
            }
            // multiply div by 10 for the next run-through
            div = div*10;
        }
    }

    public static int getKey(int i, int j) {
        return (i/j) % 10;
    }

    // test method
    public static void main(String[] args) {
        int[] list = {922, 243, 409, 885, 96, 21, -342, 119, 540, 12, -732, 8, -3, 2};
        radixSort(list);
        for (int i = 0; i < list.length; i++)
            System.out.print(list[i] + " ");
    }    
}

我标记了出现不兼容类型的行。我不想要如何修复它，但为什么类型不兼容。我真的不知道，我想了解为什么。感谢您的帮助。

Answer 1

您将存储桶声明为对象项列表，并且对象项无法转换为 int 值。所以它会在那里抛出编译错误。要修复该错误，您可以使用 @Elliott 提到的泛型，或重写代码，如下所示:

for (Object y: bucket[x]) {
   list[z] = (Integer) y;
   z++;
}