爲什麼我會將「null」作爲輸出字符串？ Java

我想要做的是從文件中讀取（在這種情況下，文件包含超過100,000行）並將值存儲在數組中，然後打印出前10行。但是，當我運行程序時，我得到第一行，然後是9行「null」，這顯然不是我想要的！這是代碼和任何提示將不勝感激。爲什麼我會將「null」作爲輸出字符串？ Java

import java.io.*; 
import java.util.Scanner; 

public class DawsonZachA5Q2{ 
    public static void main(String[] args){ 

Scanner keyboard = new Scanner(System.in); 

System.out.println("Enter a size for the number of letters for words: "); 
int size = keyboard.nextInt();//prompts user for input 
String[] array = new String[27000]; 

    try { 
     File file = new File("big-word-list.txt"); 
     Scanner scanner = new Scanner(file); 


     // Start a line count and declare a string to hold our current line. 
     int linecount=0; 

     // Tells user what we're doing 
     System.out.println("Searching for words with " + size + " letters in file..."); 
     int wordCount=0; 

     while (scanner.hasNext()){ 
      int i = 0; 
      String word = scanner.next(); 

      if(size == word.length()){ 
      wordCount++; 
      array[i]=word; 
      i++; 
      //add word to array 
      // increase the count and find the place of the word 
     } 
     } 

     linecount++; 






      System.out.println(wordCount); 

      System.out.println(wordCount+" words were found that have "+size+ " letters.");//final output 


      for(int o = 0; o<10; o++){ 
      System.out.println(array[o]); 
      } 


     scanner.close(); 
    }// our catch just in case of error 
    catch (IOException e) { 
     System.out.println("Sorry! File not found!"); 
    } 



    } // main 


} // class

來源

2015-04-07 Zhdawson

我會讓你自己想出這一個。就在'array [i] = word;'之前，添加這一行：'System.out.println（「關於在索引處設置數組」+ i）;'。然後看看會發生什麼。 – ajb

啊，是的，我明白你在說什麼了，謝謝！ – Zhdawson

定義int i = 0;外while循環。每次循環運行時它都被設置爲零。這是這裏的問題。

來源

2015-04-07 03:58:51 Ozgen

您誤入while循環。你必須在while循環之前定義'int i = 0'。在你的情況下，發生什麼是每當while循環執行，我被初始化爲0.即每次，找到所需長度的單詞，該單詞將存儲在數組[0]（因爲我每次迭代初始化爲0 while循環）替換之前存儲的值。結果，你只能得到第一個值並且其餘顯示爲空，因爲在array [1]之後沒有任何東西被存儲。因此，實際流量應該是這樣的。

// i is initialized outside of loop. 
int i = 0; 
while (scanner.hasNext()){ 
    //int i = 0; this is your error 
    String word = scanner.next(); 
    if(size == word.length()){ 
     wordCount++; 
     array[i]=word; 
     i++; 
     //add word to array 
     // increase the count and find the place of the word 
    } 
}

來源

2015-04-07 04:26:26

爲什麼我會將「null」作爲輸出字符串？ Java

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