Counts the number of "1" bits in a file.

BitCount.java

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.nio.ByteBuffer;
import java.text.MessageFormat;
import javax.swing.JFileChooser;


public class BitCount {
  public static void main(String[] args) {
    while (true) {
      JFileChooser chooser = new JFileChooser();
      int retVal = chooser.showOpenDialog(null);
      if (retVal == JFileChooser.CANCEL_OPTION) {
        break;
      }
      
      File file = chooser.getSelectedFile();
      long length = file.length();      
      System.out.println("File: " + file.getName());
      System.out.println(MessageFormat.format("Reading {0} bytes", length));
      
      byte[] buffer = new byte[4];
      long count = 0;
      try {
        InputStream input = new BufferedInputStream(new FileInputStream(file));
        
        while (input.read(buffer) > 0) {
          int i = ByteBuffer.wrap(buffer).getInt();
          count += Integer.bitCount(i);
        }
        
        long totalBits = length * 8;
        double percentage = ((double)count / (double)totalBits);
        System.out.println(MessageFormat.format(
                "Counted {0} 1s out of {1} bits ({2,number,#.##%})",
                count, totalBits, percentage
        ));
      }
      catch (Exception ex) {
        System.out.println("Error");
      }
    }
  }
}