方法在Java中没有返回任何东西

Question

我用5种方法在Java中编写了一个类。线性搜索，如果找到该值，则返回true;如果未找到，则返回false。线性搜索2，返回值的位置，如果找到。二进制搜索。它也搜索数组中的值，打印Int数组（每次打印10个数字）以及选择排序，它对数组进行排序，以便我可以执行二分搜索。一切都很好，但由于某种原因，我的方法都没有返回任何东西（void printIntArray方法除外）。

编辑：

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谢谢，伙计们，我没有意识到我需要的。出于某种原因，我认为它会自行返回价值......但另一个问题。 binarySearch方法似乎没有做任何事情。在打印语句“使用二分搜索在随机数组中搜索11”....之后，不会打印任何内容。

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编辑2： 我的binarySearch方法是行不通的，因为我不小心过中旬+ 1两种else语句（否则，如果（键<阵列[MID]）应该是中旬 - 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，我很抱歉main方法中的所有打印语句都让人分心。我想把它们拿出来以方便阅读，但我希望它能像我一直在运行它一样。

Answer 1

它们不会返回任何内容，因为您没有将返回值分配给任何变量。

使此：

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

或

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

等。

Answer 2

linearSearch(array, 30); 

他们确实会返回一些东西。但做一些与返回值！

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

或更简单：

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

在回答您的编辑

您需要启动left到1。你正在执行整数除法，它永远不会达到零。因此right卡在1和left总是比它少。

Answer 3

您必须将的排序/搜索方法调用的println()语句，否则结果将不会被打印！就像这样：

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，将结果存储在一个局部变量 - 但是，你必须将变量传递给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

他们返回他们所应该，只是你选择不对他们返回的东西做任何事情。

您可以通过在System.out.println()中包装函数调用或使用ret = yourfunction(params)存储返回值并稍后显示ret来解决此问题。