Is this a good and simple example for Singleton Pattern
For explaining the Singleton pattern the ABC naming is confusing. Just come up with some real name, e.g. Database, Logger etc. Something that might need access to a common config. Instead of System.out the config, you might want to add some mock code to init the database connection or get the logging directory.

Please keep in mind that Java classes usually are starting with a capital letter.

The static instance variable is usually called only instance.

In which context do you want to explain the pattern. Maybe we find a more suitable example?

Check http://www.oodesign.com/singleton-pattern.html for a nice explanation and some examples and drawbacks.

Please be aware that a Singleton might seem to help you sometimes in production code, but it definitely makes your life harder in testing your code. See "Dependency Injection" for an alternate approach.