Программа сравнения файлов

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;
 
public class SwinDemo implements ActionListener {
    JTextField jtfFirst, jtfSecond;
    
    JLabel jlabFirst, jlabResult;
    
    JButton jbtnComp;
 
     SwinDemo() {
    JFrame jfrm = new JFrame("Compare files");
    
    jfrm.setLayout(new FlowLayout());
    
    jfrm.setSize(200,190);
    
    jfrm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    
    jtfFirst = new JTextField(14); 
    jtfSecond = new JTextField(14);
    
    jtfFirst.setActionCommand("FileA");
    jtfSecond.setActionCommand("FileB");
    
    JButton jbtnComp = new JButton("Compare");
    
    jbtnComp.addActionListener(this);
    
    JLabel jlabFirst = new JLabel("First file: ");
    JLabel jlabSecond = new JLabel("Second file: ");
    JLabel jlabResult = new JLabel("  ");
     
    jfrm.add(jlabFirst);
    jfrm.add(jtfFirst);
    jfrm.add(jlabSecond);
    jfrm.add(jtfSecond);
    jfrm.add(jbtnComp);
    jfrm.add(jlabResult);
    
    jfrm.setVisible(true);   
     }
 
public void actionPerformed(ActionEvent ae) {
    int i, j;  i = j = 0;
    FileInputStream f1, f2;
    
    if(jtfFirst.getText().equals("")) {
        jlabResult.setText("Second file name missing ");
        return;
    }
  
    if(jtfSecond.getText().equals("")) {
        jlabResult.setText("Second file name missing ");
        return;
      }
    
    try {
f1 = new FileInputStream(jtfFirst.getText());   
    } catch(FileNotFoundException exc) {
        jlabResult.setText("First file not found ");
        return;
      }
    
    try {
        f2 = new FileInputStream(jtfSecond.getText());  
        } catch(FileNotFoundException exc) {
            jlabResult.setText("Second file not found ");
    try {
    f1.close();
        } catch(IOException exc2) {
            jlabResult.setText(" close first file ");
        }
     return;
   }
        
  try {
      do {
         i = f1.read();
         j = f2.read();
         if(i!=j) break;
     }while( i!=-1 & j!=-1);
      
      if(i != j) 
          jlabResult.setText("Files are not the same ");
      else
          jlabResult.setText("Files compare equal ");
       } catch(IOException exc) {
            jlabResult.setText("File Error ");
        }
       
       try {
           f1.close();
       } catch(IOException exc) {
           jlabResult.setText("Error closing first file ");
       }
       
       try {
           f2.close();
       } catch(IOException exc) {
           jlabResult.setText("Error closing second file ");
      }
    }
 
public static void main(String[] arqs) {
    SwingUtilities.invokeLater(new Runnable(){
        public void run() {
            new  SwinDemo();
        }
    });
  }
}

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at cl.actionPerformed(cl.java:51)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

JLabel jlabResult = new JLabel("  ");

jlabResult = new JLabel("  ");