在java中有文件读取错误

Question

需要帮助解决这个错误。我正在尝试打印字符串countryNames的数组长度。

Exception in thread "main" java.util.NoSuchElementException: No line found 
at java.util.Scanner.nextLine(Scanner.java:1516) 
at CSVReader.setUp(CSVReader.java:25) 
at CSVReader.<init>(CSVReader.java:16) 
at TestCSVReader.main(TestCSVReader.java:16) 

我正在阅读一个cvs文件，我不断收到上面的错误。下面是我的代码：

import java.io.*; 
import java.util.Scanner; 
public class CSVReader { 
//String countryNames; 
String[] countryNames; 
int yearLabels; 
int[] yearNum; 
double cellularDataTable; 
double[][] tables; 
Scanner scan; 

public CSVReader(String filename)// throws FileNotFoundException 
{ 
    setUp(filename); 
} 
private void setUp(String filename) //throws FileNotFoundException 
{ 
    File file = new File(filename); 
    try{ 
     String input=""; 
     scan = new Scanner(file); 
     scan.nextLine(); 
     while((input=scan.nextLine())!=null) 
     { 
      String[] countryNames = input.split(","); 
      //int a = Integer.parseInt(countryNames[1]); 
      System.out.println(countryNames[0]); 
      //System.out.println(a); 
     } 
     scan.close(); 
    } 
    catch(FileNotFoundException e) 
    { 
     System.out.println(e); 
    } 
} 
    public String[] getCountryNames() 
{ 
    return countryNames; 
} 

下面是我的TestCSV类文件：

public class TestCSVReader { 

/** 
* Includes test examples for class CSVReader. 
*/ 
public static void main(String[] args) 
{ 
    final String FILENAME = "data/cellular.csv"; // Directory path for Mac OS X 
    //final String FILENAME = "data\cellular.csv"; // Directory path for Windows OS (i.e. Operating System) 


    CSVReader parser = new CSVReader(FILENAME); 

    String [] countryNames = parser.getCountryNames(); 
    System.out.println(countryNames.length); 
    } 

我的CSV文件看起来像下面这样：这是因为我不希望打印出整个252个国家的汇总。基本上我接纳252个国家并将它存储在一个字符串数组中，并将它们存储在一个int数组中，并将它们存储在每个国家的蜂窝数据统计信息中。我是编程新手，想知道我是否正朝着正确的方向前进，如果不是，你将如何在一个字符串数组中输入国家名称，年代是int。并在2d双数组中统计。

CVS文件看起来像这样：

World Development Indicators 
Number of countries,252 
Country Name,1960,1961,1962,1963,1964,1965,1966,1967,1968,1969,1970,1971,1972,1973,1974,1975,1976,1977,1978,1979,1980,1981,1982,1983,1984,1985,1986,1987,1988,1989,1990,1991,1992,1993,1994,1995,1996,1997,1998,1999,2000,2001,2002,2003,2004,2005,2006,2007,2008,2009,2010,2011,2012 
Aruba,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0.029310471,0,0,2.138784453,3.605985937,3.98141538,6.16435217,13.48254011,16.50927821,57.05427692,65.05605558,72.10431377,99.64250268,103.3849507,108.1325002,112.2180618,119.2038996,126.2103374,129.72824,0,131.8565401 
Andorra,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1.307211734,1.278625641,1.250259142,4.424155104,8.538444783,13.44671556,22.12730607,32.14530928,35.99902139,43.27794118,45.77115817,68.60251444,73.82494308,79.48487497,84.27763597,78.1171579,80.2836099,82.06181111,84.06818386,83.53432222,81.50204186 
Afghanistan,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0.112598381,0.865196277,2.498055472,4.826865367,9.833164022,17.71624331,29.22037376,37.89493697,45.77817474,60.32631999,60.35299258 

Answer 1

此行while((input=scan.nextLine())!=null)尝试直到input变为null。但如果没有更多行可用，则nextLine()将引发异常。

为了避免这种情况，你的代码更改为以下

//String input=""; // this line is obsolete 
scan = new Scanner(file); 
scan.nextLine(); 
while(scan.hasNextLine()) { 
    final String input = scan.nextLine(); // read the line after the check (to make sure there is a line available) 
    String[] countryNames = input.split(","); 
    //int a = Integer.parseInt(countryNames[1]); 
    System.out.println(countryNames[0]); 
    //System.out.println(a); 
} 

Answer 2

我觉得countryNames数组为null。尝试在添加数据之前初始化它。 调试代码，并检查countryNames ...

String[] countryNames = new String[...] 

，如果你不知道数组长度，你最好使用ArrayList。 （使用ArrayList的时候，你不必先初始化。）

Answer 3

也许这样，你有一个特定的方法来测试是否扫描有更多的元素来读取

String input=""; 
scan = new Scanner(file); 
scan.nextLine(); 
while(scan.hasNext()) 
{ 
    input=scan.nextLine(); 
    String[] countryNames = input.split(","); 
    //int a = Integer.parseInt(countryNames[1]); 
    System.out.println(countryNames[0]); 
    //System.out.println(a); 
} 
scan.close(); 

Answer 4

的问题在线程提出已经解决了

while(scan.hasNextLine()) { 

但是，还有，你会在你的代码中找到了另一个问题。在循环内部，你已经创建了一个局部变量countryNames []，它与类中声明的String [] countryNames无关。

我建议你更改宣言书就是这样：

public class CSVReader {  
    List<String> countryNames; 

而且在类的构造函数初始化：

public CSVReader(String filename)// throws FileNotFoundException 
{ 
    countryNames = new ArrayList<String>(); 
    setUp(filename); 
} 

的ArrayList允许你动态添加值。因此，在循环中，您必须将每个国家/地区的名称添加到此ArrayList中：

String[] countryValues = input.split(","); 
countryNames.add(countryValues[0]);