REGEX

I am having problems creating a simple regex pattern that would match the
string
'books' followed by a backslash '\'.

In other words 'books\' without the ticks.  This appears to be a simple
pattern but I am having problems.  I've tried to create a simpler pattern
that would match a single backslash but had no luck.

linePattern1 = lineCompiler.compile ("books\\");
String test = linePattern1.getPattern();  # line 25

# Runtime Error #
Exception in thread "main" java.lang.NullPointerException
        at ModifyRegistry.main(ModifyRegistry.java:25)

Any suggestions on creating patterns with backslashes.

Thank you,

Neil