Question

I know a similar problem may have been presented here before, but i cannot find the answer on my own. To preface this, I have already found a workaround but would like to know why calling a constructor is failing. I will show the failed code and then working.

This code is a simple file analyzer, it reports the first last and ~middle (not exact) entries in a txt file. One of the requirements is recieving an argument from commandline.

Thanks for your time.

FAILED:

$ javac DataAnalyzerTester.java    
DataAnalyzerTester.java:11: cannot find symbol   
symbol  : constructor DataAnalyzer(java.lang.String)   
location: class DataAnalyzer   
analyze  = new DataAnalyzer(args[0]);    
-----------^


//DataAnalyzerTester.java

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

public class DataAnalyzerTester
{
    public static void main(String[] args)
    {
            DataAnalyzer analyze;
            analyze  = new DataAnalyzer(args[0]);
            //analyze.setFile(args[0]);
            System.out.println(analyze.min());
            System.out.println(analyze.max());
            System.out.println(analyze.avg());
    }
}


//DataAnalyzer.java
import java.util.*;
import java.io.*;

public class DataAnalyzer
{   
    public void DataAnalyzer(String fileN)
    {
        try
        {
            reader = new FileReader(fileN);
            Scanner in = new Scanner(reader);
            while(in.hasNextLine())
            {
                fileContent.add(in.nextLine());
            }
        }
        catch(IOException exception)
        {
            System.out.println("File not found. Try again Dumbass.");
        }
    }

    public void setFile(String fileN)
    {
        try
        {
            reader = new FileReader(fileN);
            Scanner in = new Scanner(reader);
            while(in.hasNextLine())
            {
                fileContent.add(in.nextLine());
            }
        }
        catch(IOException exception)
        {
            System.out.println("File not found. Try again Dumbass.");
        }
    }

    public  String min()
    {
        return fileContent.get(0);
    }

    public String max()
    {
        return fileContent.get(fileContent.size() - 1);
    }

    public String avg()
    {
        return fileContent.get((int) fileContent.size() / 2);
    }

    private FileReader reader;
    private ArrayList<String> fileContent = new ArrayList<String>();
}

---

Basically the above version does not work, but I added a setFile method to do the same thing as the constructor. My question then is why can i not call the constructor in this way? Thanks again.

Answer 1

A constructor should not specify a return type – this combined with a name matching the class is how the compiler recognizes it as a constructor. So instead of:

public void DataAnalyzer(String fileN)

write:

public DataAnalyzer(String fileN)

More information: http://download.oracle.com/javase/tutorial/java/javaOO/constructors.html