数组元素搜索

Question

我是java新手，一直在试图编写如何搜索多维数组。我的代码适用于找到的元素，但是当我输入不匹配的元素时，它不打印任何内容。请告诉我我的代码有什么问题。

import java.util.Scanner; 
public class ArraySearch { 
public static void main (String[] args){ 
    Scanner input = new Scanner(System.in); 

    //lets create the array 
    int [] [] arrayOfInts = {{1, 2,3,4}, {5,6,7,8},{9,10,11,12}}; 

    //create search variables 
    System.out.println("Enter the key number to search for in the array: "); 
    int key = input.nextInt(); 
    boolean foundIt; 

    //perform search using a for loop 
    for (int i = 0; i <arrayOfInts.length; i++){ 
     for (int j = 0; j <arrayOfInts[i].length; j++){ 
      if (arrayOfInts[i][j] == key) { 
       foundIt = true; 

       if (foundIt) { 
        System.out.println("found " + key + " at row " +i+ " column " +j); 

       } else { 
        System.out.println(key + "is not in the array"); 
       } 
      } 
     } 
    } 
} 
} 

Answer 1

你应该初始化布尔为假，因为局部变量必须在使用前进行初始化：

boolean foundIt = false; 

否则，如果没有找到钥匙，foundIt会当你访问它是未初始化在你的条件。

不初始化foundIt应该给你一个compliation错误（The local variable foundIt may not have been initialized），但是你有另一个隐藏这个错误的错误。您打印输出的if语句应该在for循环之外。现在它处于找到匹配的条件之内，所以只有在找到匹配的情况下才会对其进行评估。

Answer 2

您的包围是错误的。 if - else语句

if (foundIt) { 
    System.out.println("found " + key + " at row " +i+ " column " +j); 

} else 
     {System.out.println(key + "is not in the array"); 
} 

在for循环的检查中。

if (arrayOfInts[i][j] == key) { 

您可能希望将其放在for循环中以显示每个匹配的消息。但你应该只是把一个println消息if语句内的for循环

if (arrayOfInts[i][j] == key) { 
    System.out.println("found " + key + " at row " +i+ " column " +j); 

当从来没有发现的键打印其他消息，但是这在年底完成。确保你在开始时初始化布尔值！

boolean foundIt = false; 
... 
//at the end 
if(!foundIt) { 
    System.out.println("found " + key + " at row " +i+ " column " +j); 
} 

Answer 3

您可以将您的代码更改为以下内容。你的代码有很多问题。你必须做出的{}正确的顺序，如果你这样做，你需要初始化foundIt

Scanner input = new Scanner(System.in); 
    //lets create the array 
    int[][] arrayOfInts = {{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}}; 
    //create search variables 
    System.out.println("Enter the key number to search for in the array: "); 
    int key = input.nextInt(); 
    boolean foundIt = false; 
    for (int i = 0; i < arrayOfInts.length; i++) { 
     for (int j = 0; j < arrayOfInts[i].length; j++) { 
      if (arrayOfInts[i][j] == key) { 
      System.out.println("found " + key + " at row " + i + " column " + j); 
      // if found it will change the foundIt to true 
      foundIt = true; 
      } 
     } 
    } 
    if (!foundIt) { 
     System.out.println(key + "is not in the array"); 
    } 

Answer 4

// perform search using a for loop 
    for (int i = 0; i < arrayOfInts.length; i++) { 
     for (int j = 0; j < arrayOfInts[i].length; j++) { 
      if (arrayOfInts[i][j] == key) { 
        System.out.println("found " + key + " at row " + i + " column " 
          + j); 
        return;   
      } 
     } 
    } 
    System.out.println(key + "is not in the array"); 

我只是说上查找所需元素的回报，剪切/ else分支粘贴到的结束循环。

Answer 5

你的System.out只是这里面如果块

if (arrayOfInts[i][j] == key) 

，所以如果你没有找到的东西不打印

我会做这样：

... 
for (int i = 0; i <arrayOfInts.length; i++){ 
    for (int j = 0; j <arrayOfInts[i].length; j++){ 
     if (arrayOfInts[i][j] == key) { 
      foundIt = true; 
      // Tell where you found it 
      System.out.println("found " + key + " at row " +i+ " column " +j); 
     } 
    } 
} 
// After all check whether you found something anytime 
if(!foundIt){ 
    System.out.println(key + "is not in the array"); 
} 
... 

Answer 6

这是因为您的打印语句if（foundIt）... else块位于if（arrayOfInts [i] [j] == key）块内。这意味着如果找不到int，那么如果检查打印的位置，代码就不会进入内部。 您可以将“找不到”移动到最后。 例如：

boolean foundIt = false; 
    // perform search using a for loop 
    for (int i = 0; i < arrayOfInts.length; i++) 
    { 
     for (int j = 0; j < arrayOfInts[i].length; j++) 
     { 
      if (arrayOfInts[i][j] == key) 
      { 
       foundIt = true; 
       System.out.println("found " + key + " at row " + i + " column " + j); 
      } 

     } 
    } 
    if (!foundIt) 
    { 
     System.out.println(key + "is not in the array"); 
    } 

不要忘了首先将foundIt初始化为false。

Answer 7

我建议的解决方案是：

bool foundit=false; 

for (int i = 0; i <arrayOfInts.length; i++){ 
     for (int j = 0; j <arrayOfInts[i].length; j++){ 
      if (arrayOfInts[i][j] == key) 
      { 
      foundIt = true; 
      break; 
      System.out.println("found " + key + " at row " +i+ " column " +j); 
      } 
     } 
} 

if(!foundit) 
{ 
system.out.println("Key not found in the array.") 
} 

Answer 8

这工作：

import java.util.Scanner; 
public class ArraySearch { 
public static void main (String[] args){ 
    Scanner input = new Scanner(System.in); 

    //lets create the array 
    int [] [] arrayOfInts = {{1, 2,3,4}, {5,6,7,8},{9,10,11,12}}; 

    //create search variables 
    System.out.println("Enter the key number to search for in the array: "); 
    int key = input.nextInt(); 

    //perform search using a for loop 
    for (int i = 0; i <arrayOfInts.length; i++){ 
     for (int j = 0; j <arrayOfInts[i].length; j++){ 
      if (arrayOfInts[i][j] == key) { 
       System.out.println("found " + key + " at row " +i+ " column " +j); 
       return; 
      } 
     } 
    } 
    System.out.println(key + " is not in the array"); 
} 
} 

为什么： 命令在操作if (arrayOfInts[i][j] == key) {}只有当元素在阵列中运行，所以它是没有必要使用您的boolean foundIt;。使用return结束执行类，因为我们已经找到了我们想要的东西。行System.out.println(key + " is not in the array");应该在两个周期之后，所以它只有在我们检查过二维数组的每个元素之后才能工作。