Say you've declared a BufferedReader called "source".

The standard way to read through the lines is something like:

String curLine = source.readLine();

while ( curLine != null ) {
   System.out.println( curLine );
   curLine = source.readLine();

}

Many Java learners are bothered by the fact that this approach requires two distinct readLines.  Below are three attempts to reduce it down to a single readLine.  Explain what would go wrong if we used this loop instead of the one above:

a. 

String curLine;

while ( curLine != null ) {
   String curLine = source.readLine();
   System.out.println( curLine );
}

b. 
String curLine = "";

while ( curLine != null ) {
   String curLine = source.readLine();
   System.out.println( curLine );
}

c.
String curLine;

do {
   curLine = source.readLine();
   System.out.println( curLine );
} while ( curLine != null );

In addition to the while statement, Java also has a do-while statement.  This statement *ALWAYS* executes an iteration of the loop and then checks the while condition.  Put another way, the do-while evaluates the while at the end of the loop instead of the beginning.