java - 如何在数组中添加indexOf以及如何向数组添加元素(java)

Question

当我应该得到 0、3、6、9 时，我却一直得到 0 作为我的答案。另外如何将数组的索引添加到数组中？不确定我是否做得正确。

/**
         * This returns an int array containing a multiplication table. Your method
         * should start by allocating an array whose length is {@code numEntries} (e.g.,
         * the second parameter). You should then set the value of each entry in the
         * array equal to {@code constant} (e.g., the first parameter) times the index
         * of that entry.<br/>
         * Precondition: numEntries MUST BE 0 or larger. (PRECONDITIONS SPECIFY
         * RESPONSIBILITIES ON A METHOD'S CALLER; YOU SHOULD ASSUME THIS IS TRUE.)
         *
         * @param constant
         *            Value whose multiplication table is to be calculated.
         * @param numEntries
         *            Length of the array to be returned
         * @return Array of the appropriate length containing the multiplication table
         *         for {@code constant}.
         */
        public static int[] generateTable(int constant, int numEntries) {
            int arr[];
            arr=new int[numEntries];
            int i;
            int ans;
            for(i=0;i<arr.length;i++){
                ans=(arr[i])*constant;
                System.out.println(ans);
                arr[i]=ans;

            }
            System.out.println(arr);
            return arr;


        }
public static void main(String[] args) {
        generateTable(3,4);
    }

Answer 1

您想要ans = i *constant;。但是，我会消除 ans。我也只会在调用者中打印。就像，

public static int[] generateTable(int constant, int numEntries) {
    int[] arr = new int[numEntries];
    for (int i = 0; i < arr.length; i++) {
        arr[i] = i * constant;
    }
    return arr;
}

并且，

public static void main(String[] args) {
    System.out.println(Arrays.toString(generateTable(3, 4)));
}

当然，在 Java 8+ 中，您也可以使用 lambda 来完成此操作。就像，

public static int[] generateTable(int constant, int numEntries) {
    return IntStream.range(0, numEntries).map(i -> i * constant).toArray();
}