Code:
 FileInputStream fis = new FileInputStream("filename.txt");
        StringBuffer sbuf = new StringBuffer();
        while(true){
          int i = fis.read();
          if(i == -1) break;
          sbuf.append((char)i);
        }

Code:

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.io.FileReader;
import java.io.BufferedReader;
public class search extends JFrame                             
  {
    public String Sadrzaj = "" ;
    public String txt = "ovde ispod je sadrzaj fajla boot.ini ?";        
    public JTextField name  = new JTextField(12);             
    public JTextArea message = new JTextArea(txt, 22, 50);
        {
      FileReader Stream;
      BufferedReader File;
      String TextLine;
   try {
        Stream = new FileReader("c:\\boot.ini");
       File = new BufferedReader(Stream);
           TextLine =  File.readLine()  ; 
               while (TextLine != null) 
           {
            TextLine = File.readLine();
       System.out.println(TextLine);
           Sadrzaj = Sadrzaj + TextLine + "\n";
               }
            }
    catch(Exception e)
          {
            System.out.println("fajl je prazan ili ne postoji!" );
        String message =  "fajl je prazan ili ne postoji!";
             };
    System.out.println("ovo radi :)");
    String message = "ovo radi :)"; 
  }
    public search()                                           
          {
        message.setEditable(false);                            
        JButton enter = new JButton("E N T R E E");              
        enter.addActionListener(new action());                 
        JPanel p = new JPanel();                               
        p.setLayout(new FlowLayout());                          
        p.add(new JLabel("unesite trazenu rec"));          
        p.add(name);                                            
        p.add(enter);                                              
        p.add(message);                                           
        this.setContentPane(p);                                   
          }
    public static void main(String[] agruments)  {                
      search sal = new  search();                               
      sal.setSize(650,450);
      sal.show(); 
      sal.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
           }
 public class action implements ActionListener                 
       { 
        public void actionPerformed(ActionEvent a)              
          {
      String last = name.getText();
      int size = last.length();  
    //  message.setText( Sadrzaj );
          try {                                                 
           if (size == 0)                                       
               throw new NullPointerException();                    
              }                                                  
        catch (Exception e)
          {                                   
            message.setText("Nazalost niste uneli ni jednu rec\n\n" + Sadrzaj );  
           return;
          }
message.setText("trazili ste rec \"" + last + "\" koja sadrzi " + size + "slova\n\n" + Sadrzaj);
       }
   } 
  }