1

Im stuck with the following problem,

I've two classes, the first is readFromFile and the second class is newClass

readFromFile.java -

  • This reads a text file
  • Parses the lines of text into seperate strings
  • The values of these strings are stored in a String [ ] called dArray
  • For testing I've printed all values out and it works

newClass.java

  • This class is intended to copy the value of the string [ ] dArray into a new string and from there use the values ( for simplicity all I've included in the newClass is the code relating to copying the array)
  • What I'm doing wrong is that I'm returning dArray but its returning an array with nothing stored in it, so I either need a way to call main method from readFromFile.class / help creating a method in readFromFile that would do the same which I call from main

please help

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

public class readFromFile
{
static String[] dArray = new String [30];

   public static void main (String[] args) throws IOException
   {
      String part;
      Scanner fileScan, partScan;
      int i = 0;
      int x = 0;

     fileScan = new Scanner (new File("C:\\stuff.txt"));

     // Read and process each line of the file
      while (fileScan.hasNext())
      {
         part = fileScan.nextLine();

         partScan = new Scanner (part);
         partScan.useDelimiter(":");

         while ( partScan.hasNext()){
         dArray[i] = partScan.next();
         i++;
         }
      }
        for (x = 0;x<i;x++)
       { System.out.println(dArray[x]);
   }


   }   
        public String[] getArray()
  {
  return dArray;
           }}

newClass.java

public class newClass {

  readFromFile results = new readFromFile();// creating object from class readFromFile


 public void copyArray() { 

       String[] dArray = results.getArray();  // Trying to return the values of String [] dArray from rr classs  
                         //Method getArray in rr class is  
                         //  public String[] getArray()
                         // { return dArray; } 

        String[] arrayCopy = new String[dArray.length];

        System.arraycopy(dArray, 0, arrayCopy, 0, dArray.length);

        for (int i = 0; i < arrayCopy.length; i++)
            System.out.println(arrayCopy[i]);

    }


    public static void main(String[] args) {
       newClass.copyArray();
    }
}
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3 Answers 3

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1

Your results generation is in readFromFile.main(), but you're expecting to call it in your readFromFile(). You need to make a constructor for readFromFile, and call that in your main method, as well.

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0

The problem is that both classes have a main method. Only the class that you intend to run should have a main method, the other classes need only constructors. Assuming you want to run a unshown class it would be written like this.

public class ThirdClass{
public static void main(String[] args) {
   readFromFile reader = new ReadFromFile();
   newClass copy = new newClass();

   reader.readFromFile();
   String[] strings = reader.getArray();

   copy.copyArray(strings)

}

For this to work you need to put all of the code in the main of readFromFile in a method called "readFromFile". and you need a method in newClass that accepts a string array as an argument. Or a constructor that accepts a string array.

Make sure that neither of them have main methods or it won't work.

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3 Comments

Doesn#t the getArray() method that is in readFromFile accept a string array, only problem is when i call it it doesnt have values cause the string [] values are assigned in main method ?
I'm just saying that they can't both have main methods. Java doesn't work that way, only the program that you actually hit run on can have a main method, otherwise you have to have constructors and methods
ok i get you, so for example if i use the example you posted do i need to change public void copyArray to something else, and include Strin[] in the brackets or am I thinking about this completely wrong, thanks for you help
0
  1. Remove the static keyword before your dArray variable
  2. Change public static void main(String[] args) throws IOException in your first class to public readFromFile() throws IOException. Keep the code inside it the same.
  3. Change the line newClass.copyArray(); in your second class to (new newClass()).copyArray();
  4. Move the line in your second class readFromFile results = new readFromFile(); into the public void copyArray() method.
  5. Change public void copyArray() in your second class to public void copyArray() throws IOException
  6. Put a try..catch block around your code in the second class's main method. i.e. change (new newClass()).copyArray(); to something like try { (new newClass()).copyArray(); } catch (IOException e) { e.printStackTrace(); }

The above should get your thing working, but a friendly note would be to experiment with the code (once it works) since it's an excellent example to understand how static keywords are used, how Exceptions are handled or thrown, and how IO is used. ;)

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3 Comments

The problems are: 1. your 'dArray' variable is static. This means that only one instance of the array will ever be created and shared between ALL instances of your first class. 2. your first class has a public static void main(), instead of a constructor. This is a problem because the main() method is only called if you run the first class from the commandline, which you don't. You're calling the constructor. 3. newClass.copyArray() is a syntax error, it just won't work. copyArray() is a normal method (without the static keyword), and hence can only be called from instances of the class.
when i do as you've said ' fileScan = new Scanner (new File("C:\\stuff.txt"));' gives an error saying it must be caught or declared to be thrown. ive tried throws IOException, this only causes the same error instead to third line of newClass ' readFromFile results = new readFromFile();' if anyone could help I would be grateful ,thanks
I've updated the answer to include fixes for the cases that failed for you.

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