Question

需要帮助修复此错误。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)

我正在读取一个cvs文件，我一直收到上面的错误。以下是我的代码：

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;
}

以下是我的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文件如下所示：这是一个摘要，因为我不想打印出整个252个国家/地区。基本上我接收252个国家并将其存储在一个字符串数组中，这些年份将它们存储在一个int数组中，并将每个国家的蜂窝数据存储在一个2d双数组中。我是编程的新手，想知道我是否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命名国家，在int中的年份。和2d双数组中的统计数据。

cvs文件如下所示：

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)尝试从文件中读取单独的行，直到input变为null。但如果没有更多可用行，nextLine()将抛出异常。

要避免这种情况，请将代码更改为以下

//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

线程中提出的问题已经解决了

while(scan.hasNextLine()) {

但是您可以在代码中找到另一个问题。在循环内部，您创建了一个局部变量countryNames []，它与类中声明的String [] countryNames无关。

我建议你改变声明：

public class CSVReader {     
    List<String> countryNames;

并在类的构造函数中初始化它：

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

ArrayList允许您动态添加值。因此，在循环内部，必须将每个国家/地区名称添加到此ArrayList：

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

Answer 3

也许是这样，你有一个特定的方法来测试扫描是否有更多元素可供阅读

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

我认为countryNames数组为null。尝试在添加数据之前初始化它。调试你的代码并检查countryNames ......

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

如果您不知道阵列的长度，最好使用Arraylist。（当使用Arraylist时，你不必先进行初始化。）

从java中的文件读取错误

4 个答案: