Question

我用Java编写了一个带有5种方法的类。线性搜索，如果找到值则返回true，如果未找到则返回false。线性搜索2，如果找到则返回值的位置。二分搜索。也搜索数组中的值，打印Int数组，一次打印10个数字，选择排序，对数组进行排序，以便我可以进行二进制搜索。一切都编译得很好，但由于某种原因，我的方法都没有返回任何东西（除了void printIntArray方法）。

编辑：

谢谢，伙计们，我没有意识到我需要那个。出于某种原因，我认为它会自行返回价值......但是另一个问题。 binarySearch方法似乎没有做任何事情。在打印语句“使用二进制搜索在随机数组中搜索11”之后....，没有打印任何内容。

编辑2：我的binarySearch方法无法正常工作，因为我偶然为其他两个语句设置了mid + 1（否则if（key＆lt; array [mid]）应该是mid-1）。非常感谢大家！我添加了修复程序。

public class sortingSearching {

  public static boolean linearSearch (int [] array, int key) {
    for (int i = 0; i < array.length; i++) {
       if (array [i] == key)
           return true;
    }// end for
    return false;
}

public static int linearSearch2 (int [] array, int key) {
   for (int i = 0; i < array.length; i++) {
       if (array [i] == key)
        return i;
    }//end for
    return -1;
}//end linearSearch2

public static boolean binarySearch (int [] array, int key) {
  int left = 0;
    int right = array.length - 1;
    int mid = (left + right) /2;
       while (left <= right) {
           if (array[mid] == key)
               return true;
            else if ( key < array[mid])
               right = mid - 1;
            else 
               left = mid + 1;
            mid = (left + right) /2;
        } //end while
    return false;
}//end binarySearch

public static void printIntArray (int [] array) {
   for (int i = 0; i < array.length; i++) {
       if (i%10 == 0)
           System.out.println();
        System.out.print(array[i] + " ");
    } // end for
}

public static void selectionSort (int [] array) {
   for (int start = 0; start < array.length - 1; start ++) {
       int minI = start;
        for (int i = start + 1; i < array.length; i++)
           if (array[i] < array[start])
               minI = i;
       int temp = array[start];
    array[start] = array[minI];
       array[minI] = temp; 
    }//end for
   } //end selectionSort

public static void main (String args []) {
   int [] array = new int [20];
    for (int i =0; i < array.length; i++)
       array[i] = (int)((Math.random() * 100) + 1);

    //print the array using printArray  
    printIntArray(array);
    System.out.println();
  //use linearSearch to search for 30, 86, and 87
    System.out.println("Searching for 30 in the random array. If true is returned, " +
    "the value was found. If false was returned, the value was not found.");
      System.out.println(linearSearch(array, 30));
    System.out.println("Searching for 86 in the random array. If true is returned, " +
    "the value was found. If false was returned, the value was not found.");
       System.out.println(linearSearch(array, 86));
    System.out.println("Searching for 87 in the random array. If true is returned, " +
    "the value was found. If false was returned, the value was not found.");
       System.out.println(linearSearch(array, 87));
    //use linearSearch to locate the first occurrences of 25, 80, and 91
    System.out.println("Searching for the location of 25 in the random array. If -1 is " +
     "returned, the number was not found in the array.");
       System.out.println(linearSearch2(array, 25));
    System.out.println("Searching for the location of 80 in the random array. If -1 is " +
     "returned, the number was not found in the array.");
       System.out.println(linearSearch2(array, 80));
    System.out.println("Searching for the location of 91 in the random array. If -1 is " +
     "returned, the number was not found in the array.");
       System.out.println(linearSearch2(array, 91));
    //use selectionSort to sort the array
  selectionSort(array);
    //use binarySearch to search for 11, 28, 74, and 99
  System.out.println("Searching for 11 in the random array using binary search. If true is returned, " +
    "the value was found. If false was returned, the value was not found.");
       System.out.println(binarySearch (array, 11));
  System.out.println("Searching for 28 in the random array using binary search. If true is returned, " +
    "the value was found. If false was returned, the value was not found.");
       System.out.println(binarySearch (array, 28));
  System.out.println("Searching for 74 in the random array using binary search. If true is returned, " +
    "the value was found. If false was returned, the value was not found.");
       System.out.println(binarySearch (array, 74));
  System.out.println("Searching for 99 in the random array using binary search. If true is returned, " +
    "the value was found. If false was returned, the value was not found.");
       System.out.println(binarySearch (array, 99));
} //end main


} //end sortingSearching

另外，对不起，主方法中的所有打印语句都让人分心。为了方便阅读，我想把它们拿出去，但我希望它和我一直在运行它一样。

Answer 1

linearSearch(array, 30);

他们确实会回报一些东西。但做一些具有回报价值的东西！

boolean value = linearSearch(array, 30);
System.out.println(value);

甚至更简单：

System.out.println(linearSearch(array, 30));

回复您的修改

您需要left启动1。你正在执行整数除法，它永远不会达到零。因此，right卡在1上，left总是小于它。

Answer 2

它们不会返回任何内容，因为您没有将返回值赋给任何变量。

制作本：

boolean foo= linearSearch(array, 86);
System.out.println(foo);

或

System.out.println(linearSearch(array, 86));

等等。

Answer 3

您必须将排序/搜索方法调用在 println()语句中，否则结果将无法打印！像这样：

System.out.println(
    "Searching for 30 in the random array. If true is returned, " +
    "the value was found. If false was returned, the value was not found." + 
    linearSearch(array, 30));

或者，将结果存储在局部变量中 - 但同样，您必须将变量传递给println()：

boolean result = linearSearch(array, 30);
System.out.println(
    "Searching for 30 in the random array. If true is returned, " +
    "the value was found. If false was returned, the value was not found." + 
    result);

Answer 4

他们返回他们应该做的事情，只是你选择不对他们返回的东西做任何事情。

您可以通过将函数调用包装在System.out.println()中，或使用ret = yourfunction(params)存储返回值并稍后显示ret来解决问题。

方法不会在Java中返回任何内容

4 个答案: