如何使所有这些值都为正

Question

我需要更改主体以使所有这些值为正，但我不确定@param arr != null是什么意思或如何使用它。我也不确定数组是如何工作的以及空值是如何工作的，这对我来说非常令人困惑。我也不明白为什么每当我尝试更改某些代码时，它总是会给我语法错误。

import java.util.Arrays;
public class ArraysPractice
{
  /**
 * Do not change any values in the main method below.
*/
public static void main(String[] args)
  {
int[] array1 = {2, 42, 1};
int[] array2 = {4, -1, -3, 0, 8, -4, 2};
int[] array3 = {-8, 42, 1, 42, -1, 1, -2, 42, -5, 0, 2, 42};
System.out.println("sumUpValuesInArray test:");
System.out.println(sumUpValuesInArray(array1) == 45 ? "Passed!"
  : "Expected 45 but you returned " + sumUpValuesInArray(array1));
System.out.println(sumUpValuesInArray(array2) == 6 ? "Passed!"
  : "Expected 6 but you returned " + sumUpValuesInArray(array2));
System.out.println(sumUpValuesInArray(array3) == 156 ? "Passed!"
  : "Expected 156 but you returned " + sumUpValuesInArray(array3));
System.out.println("ncount42's test:");
System.out.println(count42s(array1) == 1 ? "Passed!"
  : "Expected 1 but you returned " + count42s(array1));
System.out.println(count42s(array2) == 0 ? "Passed!"
  : "Expected 0 but you returned " + count42s(array2));
System.out.println(count42s(array3) == 4 ? "Passed!"
  : "Expected 4 but you returned " + count42s(array3));
System.out.println("nfindFirstLocation test");
System.out.println(findFirstLocation(array1, 42) == 1 ? "Passed!"
  : "Expected 1 but you returned " + findFirstLocation(array1, 42));
System.out.println(findFirstLocation(array1, 44) == -1 ? "Passed!"
  : "Expected -1 but you returned " + findFirstLocation(array1, 44));
System.out.println(findFirstLocation(array2, 8) == 4 ? "Passed!"
  : "Expected 4 but you returned " + findFirstLocation(array1, 8));
System.out.println(findFirstLocation(array2, 18) == -1 ? "Passed!"
  : "Expected -1 but you returned " + findFirstLocation(array1, 18));
System.out.println(findFirstLocation(array3, 42) == 1 ? "Passed!"
  : "Expected 1 but you returned " + findFirstLocation(array1, 42));
System.out.println("nmakeThemAllPostive test:");
makeThemAllPostive(array1);
String actual = Arrays.toString(array1);
System.out.println(actual.equals("[2, 42, 1]") ? "Passed!"
  : "Expected [2, 42, 1] but you returned " + actual);
makeThemAllPostive(array2);
actual = Arrays.toString(array2);
System.out.println(actual.equals("[4, 1, 3, 0, 8, 4, 2]") ? "Passed!"
  : "Expected [4, 1, 3, 0, 8, 4, 2] but you returned " + actual);
makeThemAllPostive(array3);
actual = Arrays.toString(array3);
System.out.println(
  actual.equals("[8, 42, 1, 42, 1, 1, 2, 42, 5, 0, 2, 42]") ? "Passed!"
    : "Expected [8, 42, 1, 42, 1, 1, 2, 42, 5, 0, 2, 42] but you returned "
      + actual);
}
 /**
  * Given a non-null array, return the sum of all elements.
  * 
  * @param arr
 *          != null
* @return sum of all elements
*/
public static int sumUpValuesInArray(int[] arr)
{
 // TODO: Complete the body of this method so that all of the tests say
  // Passed! in the console.
  return 42;
  // Integer array1 = null;
  // return Integer int[] array4;
 }
  /**
 * Given a non-null array, count the number of elements that are 42.
 * 
* @param theArray
 *          != null
 * @return number of elements that are 42.
 */
public static int count42s(int[] theArray)
   {
    // TODO: Complete the body of this method so that all of the tests 
 say
    // Passed! in the console.
    return 42;
  }
/**
 * Given a non-null array, return the index of the first location of 
value
 * found from the beginning of the array. If the item is not in the 
array,
 * return -1.
 * 
 * @param arr
 *          != null
* @param value
 *          may or may not be in the array.
 * @return
 */
public static int findFirstLocation(int[] arr, int value)
     {
      // TODO: Complete the body of this method so that all of the tests 
say
    // Passed! in the console.
  return 42;
}
/**
 * Removes the negative signs from all values in the array. This 
mutates the
   * original array and changes the values in it.
 * 
 * @param arr
 *          !=null
 */
public static void makeThemAllPostive(int[] arr)
{
    // TODO: Complete the body of this method so that all of the tests 
say
    // Passed! in the console.
   int[] array2 * != null;

 //   int[] array2 = new int[] {4, 1, 3, 0, 8, 4, 2};
   // int[] array3 = new int[] {8, 42, 1, 42, 1, 1, 2, 42, 5, 0, 2, 42};
}
}

Answer 1

您在

中看到的@param arr != null

/**
 * Removes the negative signs from all values in the array. This mutates the
 * original array and changes the values in it.
 * 
 * @param arr
 *          !=null
 */

实际上是JavaDoc评论的一部分（另见维基百科）

@param 标签描述一个参数（下一个单词，在你的情况下arr），描述的其余部分（!= null）只是 JavaDoc 注释的作者添加为参数描述的内容。

此描述似乎是作者的暗示，即您的代码不应期望null作为该参数的有效参数，并且如果仍然传递null值而不是数组，则可以执行任何它喜欢的操作。