java - 复制和修改数组元素

Question

这是原始提示:

Write a loop that sets newScores to oldScores shifted once left, with element 0 copied to the end. Ex: If oldScores = {10, 20, 30, 40}, then newScores = {20, 30, 40, 10}.

Note: These activities may test code with different test values. This activity will perform two tests, the first with a 4-element array (newScores = {10, 20, 30, 40}), the second with a 1-element array (newScores = {199}). See How to Use zyBooks.

Also note: If the submitted code tries to access an invalid array element, such as newScores[9] for a 4-element array, the test may generate strange results. Or the test may crash and report "Program end never reached", in which case the system doesn't print the test case that caused the reported message.

这是我的代码:

public class StudentScores {
  public static void main (String [] args) {
  final int SCORES_SIZE = 4;
  int[] oldScores = new int[SCORES_SIZE];
  int[] newScores = new int[SCORES_SIZE];
  int i = 0;

  oldScores[0] = 10;
  oldScores[1] = 20;
  oldScores[2] = 30;
  oldScores[3] = 40;

  for (i = 0; i < SCORES_SIZE - 1; i++) {
     newScores[3] = oldScores[0];
     newScores[i] = oldScores[i + 1]; 
  }

  for (i = 0; i < SCORES_SIZE; ++i) {
     System.out.print(newScores[i] + " ");
  }
  System.out.println();

  return;
 }
 }

这是我的输出:

测试旧分数 = {10, 20, 30, 40}

您的输出:20 30 40 10

✖ 测试 oldScores = {199}

预期输出:199

你的输出:0

为什么我的第二次输出测试得到 0？

Answer 1

在 for 循环中复制 oldscores 中的值至newscores在 SCORES_SIZE == 1 的情况下永远不会运行，自 SCORES_SIZE - 1 == 0 ，和0 < 0立即为假。

移动newScores[SCORES_SIZE - 1] = oldScores[0]; for 循环外的行:

for (i = 0; i < SCORES_SIZE - 1; i++) {
  newScores[i] = oldScores[i + 1]; 
}
newScores[SCORES_SIZE - 1] = oldScores[0];