Java.io and java.swing help

Question

i'm writing a program that write the byte representation of numbers and outputs them to a joptionpane window
it keeps telling me that void functions are not allowed
is there any way that i can use void functions in my output? or would i need to change to a method that returns a value?
here is my code, please help me, it will be greatly appreciated :)
GUI Part
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class zero2nineTest extends JFrame{
     zero2nine show;
     public static void main(String[] args){
          zero2nineTest x = new zero2nineTest();
          x.setVisible(true);
     public zero2nineTest(){
          super("File IO and Byte Representation Tests");
          Container cp = getContentPane();
          cp.setLayout(new FlowLayout());
          JButton readFile1 = new JButton("Create and Read 1st Byte Representations");
          readFile1.addActionListener(new ActionListener(){
               public void actionPerformed(ActionEvent e){
                    zero2nine.writeFile(out);
                    JOptionPane.showMessageDialog(
                         zero2nineTest.this,
                         "Odd numbers: " + zero2nine.readFile(), "Byte Representation of Odd Numbers",
                         JOptionPane.PLAIN_MESSAGE);
               cp.add(readFile1);
          JButton readFile2 = new JButton("Create and Read 2nd Byte Representations");
          readFile1.addActionListener(new ActionListener(){
               public void actionPerformed(ActionEvent e){
                    zero2nine.writeFile2(out);
                    JOptionPane.showMessageDialog(
                         zero2nineTest.this,
                         "Even numbers: " + zero2nine.readFile2(), "Byte Representation of Even Numbers",
                         JOptionPane.PLAIN_MESSAGE);
               cp.add(readFile2);
          JButton quit = new JButton("Quit Program");
          quit.addActionListener(new ActionListener(){
               public void actionPerformed(ActionEvent e){
                    int decision;
                    decision = JOptionPane.showConfirmDialog(
                         null, "Are you sure?", "Are you sure?", JOptionPane.YES_NO_OPTION);
                         if(decision == 0){
                              System.exit(0);
               cp.add(quit);
               pack();
Class Part
import java.io.*;
class zero2nine{
     static String fileName = "zero2nine.txt";
//     public static void main(String[] args){
//          try{
//               FileOutputStream out = createFile();
//               writeFile(out);
//               writeFile2(out);
//               readFile();
//               readFile2();
//          }catch(IOException io){
//               System.out.println("closing program");
     static FileOutputStream createFile() throws IOException{
          File f = new File(fileName);
          FileOutputStream out = new FileOutputStream(f);
          return out;
     static void writeFile(FileOutputStream out) throws IOException{
          DataOutputStream ds = null;
          try{
               ds = new DataOutputStream(out);
               int x = 0;
               for(int i = 0; i < 10; i++){
                    x = i * i;
                    ds.writeInt(x);
          }finally{
               System.out.println("File written this far");
     static void writeFile2(FileOutputStream out) throws IOException{
          DataOutputStream ds = null;
          try{
               ds = new DataOutputStream(out);
               int x = 0;
               for(int i = 10; i < 20; i++){
                    x = i * i;
                    ds.writeInt(x);
          }finally{
               System.out.println("File written this far again");
     public int readFile() throws IOException{
          DataInputStream dataIn = null;
          try{
               FileInputStream in = new FileInputStream("zero2nine.txt");
               dataIn = new DataInputStream(in);
               //Output odd numbers
               for(int i = 0; i < 10; i++){
                    if(dataIn.readInt() % 2 == 0){
                         int b = dataIn.readInt();
                         System.out.println(b);
          }finally{
               System.out.println("File read this far");
               return(b);
     static void readFile2() throws IOException{
          DataInputStream dataIn = null;
          try{
               FileInputStream in = new FileInputStream("zero2nine.txt");
               dataIn = new DataInputStream(in);
               //Output even numbers
               for(int i = 10; i < 20; i++){
                    if(dataIn.readInt() % 2 == 1){
                         int b = dataIn.readInt();
                         System.out.println(b);
          }finally{
               System.out.println("File read this far again");
}

Answer 1

F:\Computer Science\Java\zero2nineTest.java:28: cannot resolve symbol
symbol: variable out
                    zero2nine.writeFile(out);
^
               public void actionPerformed(ActionEvent e){
                    zero2nine.writeFile(out);
                    JOptionPane.showMessageDialog(
F:\Computer Science\Java\zero2nineTest.java:31: 'void' type not allowed here
                         "Odd numbers: " + zero2nine.readFile(), "Byte Representation of Odd Numbers",
^
                         zero2nineTest.this,
                         "Odd numbers: " + zero2nine.readFile(), "Byte Representation of Odd Numbers",
                         JOptionPane.PLAIN_MESSAGE);
F:\Computer Science\Java\zero2nineTest.java:41: cannot resolve symbol
symbol: variable out
                    zero2nine.writeFile2(out);
^
                    zero2nine.writeFile2(out);
                    JOptionPane.showMessageDialog(
                         zero2nineTest.this,
F:\Computer Science\Java\zero2nineTest.java:44: 'void' type not allowed here
                         "Even numbers: " + zero2nine.readFile2(), "Byte Representation of Even Numbers",
^
                         zero2nineTest.this,
                         "Even numbers: " + zero2nine.readFile2(), "Byte Representation of Even Numbers",
                         JOptionPane.PLAIN_MESSAGE);
4 errors
Tool completed with exit code 1