錯誤解析文件 - 運行時錯誤

Question

import java.io.File; 
import java.util.Scanner; 
import java.io.FileNotFoundException; 
import java.lang.IllegalStateException; 
import java.util.NoSuchElementException; 
import java.util.List; 
import java.util.ArrayList; 
import java.util.StringTokenizer; 

public class database { 
    String fileName; 
    Scanner input; 
    String data[][]; 
    List<String> records; 

    public database(String fileName) { 
     fileName = "C:/Users/lucifer/Desktop/input.txt"; 
    } 

    public void openFile() { 
     try { 
      input = new Scanner(new File("C:/Users/lucifer/Desktop/input.txt")); 
     } catch (FileNotFoundException e) { 
      // TODO Auto-generated catch block 
      e.printStackTrace(); 
     } 
    } 

    public void readRecords() { 
     // Read all lines (records) from the file into an ArrayList 
     records = new ArrayList<String>(); 
     try { 
      while (input.hasNext()) 
       records.add(input.nextLine()); 
      System.out.println(records); 

     } catch (Exception e) { 
      // TODO: handle exception 
     } 

    } 

    public void parseFields() { 
     String delimiter = ",\n"; 

     // Create two-dimensional array to hold data (see Deitel, p 313-315) 
     int rows = records.size(); // #rows for array = #lines in file 
     data = new String[rows][]; // create the rows for the array 
     int row = 0; 

     for (String record : records) { 
      StringTokenizer tokens = new StringTokenizer(record, delimiter); 
      int cols = tokens.countTokens(); 
      data[row] = new String[cols]; // create columns for current row 
      int col = 0; 
      while (tokens.hasMoreTokens()) { 
       data[row][col] = tokens.nextToken().trim(); 
       // System.out.print(data[row][col] + " "); 
       col++; 
      } 



     } 

    } 

    public static void main(String[] args) { 

     database file1 = new database(null); 
     file1.openFile(); 
     file1.readRecords(); 

     file1.parseFields(); 
      printMatrix(file1.data); 

    } 

    static void printMatrix(String[][] grid) { 
     for (int r = 0; r < grid.length; r++) { 
      for (int c = 0; c < grid[r].length; c++) 
       System.out.print(grid[r][c] + " "); 
      System.out.println(); 
     } 
    } 

} 

在這裏我解析逗號分隔的文件使用掃描儀。 爲什麼這段代碼在打印數據數組時拋出異常？？

Answer 1

我花了一段時間，但我發現它：

在parseFields您發起INT行= 0;但不要在每個循環中執行row++，以便覆蓋同一行。當您到達printMatrix時，您嘗試打印未初始化的行。那麼你會得到例外。

變化parseFields到：

public void parseFields() { 
    String delimiter = ",\n"; 

    // Create two-dimensional array to hold data (see Deitel, p 313-315) 
    int rows = records.size(); // #rows for array = #lines in file 
    data = new String[rows][]; // create the rows for the array 
    int row = 0; 

    for (String record : records) { 
     StringTokenizer tokens = new StringTokenizer(record, delimiter); 
     int cols = tokens.countTokens(); 
     data[row] = new String[cols]; // create columns for current row 
     int col = 0; 
     while (tokens.hasMoreTokens()) { 
      data[row][col] = tokens.nextToken().trim(); 
      // System.out.print(data[row][col] + " "); 
      col++; 
     } 

     row++; 
    } 
} 

Answer 2

您還沒有parsefield更新row，嘗試用

public void parseFields() { 
     String delimiter = ",\n"; 

     // Create two-dimensional array to hold data (see Deitel, p 313-315) 
     int rows = records.size(); // #rows for array = #lines in file 
     data = new String[rows][]; // create the rows for the array 
     int row = 0; 

     for (String record : records) { 
      StringTokenizer tokens = new StringTokenizer(record, delimiter); 
      int cols = tokens.countTokens(); 
      data[row] = new String[cols]; // create columns for current row 
      int col = 0; 
      while (tokens.hasMoreTokens()) { 
       data[row][col] = tokens.nextToken().trim(); 
       // System.out.print(data[row][col] + " "); 
       col++; 
      } 
      row++; 
     } 

    } 

Answer 3

在方法parseFields（），你需要添加行++;

public void parseFields() { 
    String delimiter = ",\n"; 

    // Create two-dimensional array to hold data (see Deitel, p 313-315) 
    int rows = records.size(); // #rows for array = #lines in file 
    data = new String[rows][]; // create the rows for the array 
    int row = 0; 

    for (String record : records) { 
     StringTokenizer tokens = new StringTokenizer(record, delimiter); 
     int cols = tokens.countTokens(); 
     data[row] = new String[cols]; // create columns for current row 
     int col = 0; 
     while (tokens.hasMoreTokens()) { 
      data[row][col] = tokens.nextToken().trim(); 
      // System.out.print(data[row][col] + " "); 
      col++; 
     } 

    row++; //////////////Here 

    } 

}