java - 在java中读取流文件

Question

我正在处理逗号分隔值文件。我想从每个原始文件中提取第一个位置 [数组中的“0”位置] 值，并希望对其进行一些数学计算。

csv inputfile is like this
a,b,c,d
12,32,45,76
23,45,77,56
32,34,49,28
73,92,26,68
73,36,77,26

为了获得第一名，它给我这样的错误

Exception in thread "main" java.lang.NumberFormatException: For input string: ""12"
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1268)

at java.lang.Double.parseDouble(Double.java:548)
    at rotation.pkg45.Rotation45.main(Rotation45.java:49)//code line no-49

它在第二个和第三个位置上工作正常，但对于第四个位置它给出与第一个相同的错误。

 package rotation.pkg45;import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.io.FileWriter;
import java.io.*;
import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.ListIterator;
public class Rotation45 {
 public static void main(String[] args)throws IOException {
        String filename = "bank-full2.csv";
        ArrayList<String> namesList = new ArrayList<String>( );
        String[] t1;
       // StringBuilder sb;
        List<Double> list = new ArrayList<Double>();
        File file = new File(filename);
        BufferedWriter writer = null;

        try {
            writer = new BufferedWriter(new FileWriter("bank2test1.csv"));     
               double a1=0.866025;
        double a2=0.5;
        double a3=-0.5;
        double a4=0.866025;
        double b1;
        double b2;
        double c1;
        double c2;          

            Scanner inputStream = new Scanner(file);
            inputStream.next();  
             Scanner inputStreamm = new Scanner(file);
            inputStreamm.next();          

         while (inputStreamm.hasNext()) {   //while loop for find MEAN
            String data = inputStreamm.next();   //read each line and store in data
            String[] values = data.split(",");  //every line splited with " ; " and store each attribute in string list 

            double first = Double.parseDouble(values[1]); 


          /* no suchelementexeption  */  String data1 = inputStreamm.next();   //read each line and store in data
            String[] values1 = data1.split(",");  
            //inputStream.next();          
            double second = Double.parseDouble(values1[1]); 

            c1= ((a2*second)+(a1*first));
    c2= ((a3*first)+(a4*second));
       values1[2] = String.valueOf(c2);
        values[2] = String.valueOf(c1);
       StringBuilder sb = new StringBuilder();
            //  String newData = sb.toString();
            for (int i = 0; i<values.length ; i++) {
                    sb.append(values[i]);
                    if (i < values.length - 1) {
                    sb.append(",");
                }
                    }
             sb.append("\n");
              for (int i = 0; i<values1.length ; i++) {
                    sb.append(values1[i]);
                    if (i < values.length - 1) {
                    sb.append(",");
                }
                    }
            // get the new string
           // System.out.println(sb.toString());

            writer.write(sb.toString()+"\n");
                }
            writer.close();

            inputStreamm.close();


            }
        catch (FileNotFoundException ex)
              {
            Logger.getLogger(Rotation45.class.getName()).log(Level.SEVERE, null, ex);
        }

    }
}              

例如，这里我提取了值[1](表示数组中的第二个位置，如 32,45,34,..)

so result will be..
12,34,45,76
23,46,77,56
32,36,49,28
73,93,26,68
73,38,77,26

此代码适用于 values[1] 和 value[2] 而不是 values[0] 和 value[3]..为什么我不明白请帮助我...

Answer 1

当您阅读该行时，它显然会返回周围的引号，例如:

"12,32,45,76"

所以当你拆分它时，你会得到以下元素:

"12
32
45
76"

如您所见，行中的第一个和最后一个元素不是数字，因此您的 Double.ParseDouble(..) 调用失败。

您应该修改原始字符串(通过对其进行子字符串化或更好地使用 .reaplce("\"", ""))或在拆分后检查每个元素然后替换/修剪引号。