C-style Input Loop

Here is the loop from the copyFile() method.

  line = source.readLine();
  while ( line != null )
  {
   dest.write(line);
   dest.newLine();
   line = source.readLine();
  }

Here is the same loop written in a style that is commonly used with the C programming language. This style also works for Java:

  while ( (line = source.readLine()) != null )
  {
   dest.write(line);
   dest.newLine();
  }

The key to understanding this is to understand that an assignment statement is an expression and has a value. That value is the value that is assigned to the variable. So this:

(line = source.readLine())

has a value that is non-null after a successful readLine() and null upon end-of-file. Say that the file has data in it:

This may be more bother than it is worth, but programmers familiar with C are likely to use this style, so you will see it often.