public class Receiver {
public static void main(String [] args){
if(args.length < 2) {
System.err.println(“Please invoke with
java Receiver <file> <millis>”);
return;
}

String file = args[0];
Integer millis = Integer.parseInt(args[1]);

LinkedList <Integer> l = new LinkedList<
Integer>();
int conone = 0;
while(true){
int temp = read(file);

if(conone < 8){
if(temp == 1){
conone++;
} else {
conone = 0;
}
} else {
l.add(temp);
if(l.size() == 8){
String c = “”;

while(l.size() > 0){
c += l.getFirst();
l.removeFirst();
}

System.out.print((char) Integer.
parseInt(c, 2));
conone = 0;
}
}

sleep(millis);
}
}

public static void sleep(Integer millis){
try { Thread.sleep(millis); } catch(Exception e){
e.printStackTrace(); }
}

public static int read(String f){
try{
// open a channel
FileChannel channel =
new RandomAccessFile(new File(f), “rw”).getChannel();
FileLock lock = channel.tryLock();
if(lock == null)
return 1;

// give up lock
if(lock != null)
lock.release();

channel.close();
} catch(Exception e){
e.printStackTrace();
}

// no lock
return 0;
}

public class Sender {

public static void main(String [] args){
if(args.length < 3) {
System.err.println(“Please invoke with
java Sender <file> <content file name> <millis>”);
return;
}

String file = args[0];

// load some data
String line=“”;
String total=“”;
try {
BufferedReader b =
new BufferedReader(new FileReader(args[1]));
while((line=b.readLine()) != null){
total += line + “\n”;
}
} catch(Exception e){
e.printStackTrace();}

char [] content = total.toCharArray();
Integer millis = Integer.parseInt(args[2]);

// content
for(char temp : content){

// preamble
for(int i = 0; i < 8; i++){
lock(file, millis);
}

String bits = Integer.toBinaryString((int) temp);

while(bits.length() < 8){
bits = “0″ + bits;
}

for(char bit : bits.toCharArray()){
if(bit == ‘1′){
lock(file, millis);
} else {
sleep(millis);
}

System.out.print(bit);
}
}
}

public static void sleep(Integer millis){
try { Thread.sleep(millis); } catch(Exception e){
e.printStackTrace(); }
}

public static void lock(String file, int millis){
try{
// open a channel
FileChannel channel =
new RandomAccessFile(new File(file), “rw”).getChannel();

// get a lock
FileLock lock = null;
while(lock == null){
lock = channel.lock();
}

// Sleep
sleep(millis);