How to make the user choose file.

Question

I am making a program in which a file is read using RandomAcessFile. I wamt the user to choose the file from its location. I am giving the code. Just help me in knowing where the error is.
import java.awt.*;
import java.awt.event.*;
public class ChooseFiles{
     public static void main(String[] args){
          getFiles();
     public static String getFiles(){
          DialogFrames df = new DialogFrames("MedInfo");
          df.setSize(800,555);
          df.addWindowListener(new WindowAdapter(){
               public void windowClosing(WindowEvent we){
                    System.exit(0);
          df.show();
          return df.getFile();
class DialogFrames extends Frame implements ActionListener{
     Menu m = new Menu("File");
     MenuBar mb = new MenuBar();
     MenuItem mi = new MenuItem("Open");
     FileDialog fd;
     DialogFrames(String title){
          super(title);
          setLayout(new GridLayout(1,1));
          m.add(mi);
          mi.addActionListener(this);
          mb.add(m);
          setMenuBar(mb);
          fd = new FileDialog(this,"Open");
     public void actionPerformed(ActionEvent ae){
          if (ae.getSource()==mi){
               fd.setVisible(true);
     public String getFile(){
          return fd.getFile();
import java.io.*;
public class Plot{
     boolean flag = true;
     ChooseFiles cf = new ChooseFiles();
     public static void main(String[] args){
          try{
               String ftr = cf.getFiles();
               RandomAccessFile raf = new RandomAccessFile(ftr,"r");
               long l = 0;
               while (l < raf.length()){
                    String str = raf.readLine().toString();
                    l = raf.getFilePointer();
                    if (str != null){
                         System.out.println("This line is " str" at l = "+l);
               raf.close();
          }catch (Exception e){
               System.out.println("Caught Exception " + e.toString());
I get the following compilation error. Please help me to sort it out.
Plot.java:7: Can't make a static reference to nonstatic variable cf in class Plot.
String ftr = cf.getFiles();
^

Answer 1

I made the changes to Plot.java.
This is the first one.
import java.io.*;
public class Plot{
     boolean flag = true;
     public static void main(String[] args){
          Plot plot = new Plot();
     Plot(){
          try{
               String ftr = "";
               ChooseFiles cf = new ChooseFiles();
               ftr += cf.getFiles();
               RandomAccessFile raf = new RandomAccessFile(ftr,"r");
               long l = 0;
               while (l < raf.length()){
                    String str = raf.readLine().toString();
                    l = raf.getFilePointer();
                    if (str != null){
                         System.out.println("This line is " str" at l = "+l);
               raf.close();
          }catch (Exception e){
               System.out.println("Caught Exception " + e.toString());
It gives the following exception.
Caught Exception java.io.FileNotFoundException: null (The system cannot find the file specified)
This is the second one.
import java.io.*;
public class Plot{
     boolean flag = true;
     public static void main(String[] args){
          Plot plot = new Plot();
     Plot(){
          try{
               ChooseFiles cf = new ChooseFiles();
               String ftr = cf.getFiles();
               RandomAccessFile raf = new RandomAccessFile(ftr,"r");
               long l = 0;
               while (l < raf.length()){
                    String str = raf.readLine().toString();
                    l = raf.getFilePointer();
                    if (str != null){
                         System.out.println("This line is " str" at l = "+l);
               raf.close();
          }catch (Exception e){
               System.out.println("Caught Exception " + e.toString());
Caught Exception java.lang.NullPointerException