Print uppercase/lowercase and reverse from input to output using a Thread

Question

I'm trying to read each line from input.txt and print each line so each letter in the input line turns uppercase if it is lowercase, and turns lowercase if it is uppercase. Additionally, I'd like to use a Thread to do this, as I'd also like to print the reverse of each line also.

I get an error for printUppLow uppLow = new printUppLow(); and printRev rev = new printRev();

non-static variable this cannot be referenced from a static context.

Code

public static void main(String args[])
{
    String inputfileName="input.txt";     // A file with some text in it
    String outputfileName="output.txt";   // File created by this program
    String oneLine;

    try {
        // Open the input file
        FileReader fr = new FileReader(inputfileName);
        BufferedReader br = new BufferedReader(fr);

        // Create the output file
        FileWriter fw = new FileWriter(outputfileName);
        BufferedWriter bw = new BufferedWriter(fw);

        printRev rev = new printRev();
        printUppLow uppLow = new printUppLow();
        rev.start();
        uppLow.start();

        // Read the first line
        oneLine = br.readLine();
        while (oneLine != null) { // Until the line is not empty (will be when you reach End of file)

            // Print characters from input file
            System.out.println(oneLine);  

            bw.newLine();
            // Read next line
            oneLine = br.readLine(); 
        }

        // Close the streams
        br.close();
        bw.close();
    } catch (Exception e) {
        System.err.println("Error: " + e.getMessage());
    }
}


public class printUppLow extends Thread 
{
    public void run(String str)
    {
        String result = ""; 
        for (char c : str.toCharArray()) 
        { 
            if (Character.isUpperCase(c)){ 
                result += Character.toLowerCase(c); // Convert uppercase to lowercase
            } 
            else{ 
                result += Character.toUpperCase(c); // Convert lowercase to uppercase
            } 
        } 
        return result;  // Return the result
    }
}

public class printRev extends Thread
{
    public void run()
    {
        StringBuffer a = new StringBuffer("input.txt");
        System.out.println(a.reverse());
    }
}

Answer 1

That is because the nested classes printUppLow and printRev are not declared static, and therefore are instance-relative.

To solve this, declare them out of your main class, or declare add the static keyword in their declaration.

(By the way, you'll probably get complaints that you don't name your classes with an uppercase.)

Answer 2

This is an example using nested Classes for Runnable interface.

package co.edu.unbosque.jn.in2outtext;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

/**
 * @author Alejandro
 */
public class FileManager {

    private File toRead;

    BufferedReader br;

    public FileManager(String fileIN) throws FileNotFoundException {
        this.toRead = new File(fileIN);
        if (!this.toRead.exists()) {
            throw new IllegalArgumentException("File doesn't exist");
        }
        br = new BufferedReader(new FileReader(toRead));
    }

    public String reverseUpLowReadLine() throws IOException {
        String line = br.readLine();
        StringBuilder newSt = new StringBuilder();
        if (line != null) {
            for (Character c : line.toCharArray()) {
                if (Character.isLowerCase(c)) {
                    newSt.append(Character.toUpperCase(c));
                } else {
                    newSt.append(Character.toLowerCase(c));
                }
            }
        } else {
            br.close();
            return null;
        }
        return newSt.toString();
    }

    public String reverseLine() throws IOException {
        String line = br.readLine();
        if (line != null) {
            StringBuilder sb = new StringBuilder(line);
            return sb.reverse().toString();
        } else {
            br.close();
            return null;
        }
    }
}

=============================================================

package co.edu.unbosque.jn.in2outtext;

        import java.io.FileNotFoundException;
        import java.io.IOException;
        import java.util.logging.Level;
        import java.util.logging.Logger;

/**
 * @author Alejandro Leon
 */
public class In2Out {
    public static void main(String[] args) {
        String inFile = "In.txt";
        try {
            final FileManager fm = new FileManager(inFile);
            Thread t = new Thread(new Runnable() {
                @Override
                public void run() {
                    String s = null;
                    do {
                        try {
                            s = fm.reverseLine();
                            if (s != null) {
                                System.out.println(s);
                            }
                        } catch (IOException ex) {
                            Logger.getLogger(In2Out.class.getName()).log(Level.SEVERE, null, ex);
                        }
                    } while (s != null);
                }
            });
            final FileManager fm2 = new FileManager(inFile);
            Thread t2 = new Thread(new Runnable() {
                @Override
                public void run() {
                    String s = null;
                    do {
                        try {
                            s = fm2.reverseUpLowReadLine();
                            if (s != null) {
                                System.out.println(s);
                            }
                        } catch (IOException ex) {
                            Logger.getLogger(In2Out.class.getName()).log(Level.SEVERE, null, ex);
                        }
                    } while (s != null);
                }
            });
            t.start();
            t2.start();
        } catch (FileNotFoundException ex) {
            Logger.getLogger(In2Out.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}