Michael ss thinks this is interesting: A class declaration may contain a declaration of another class, which is then called a member class of the outer declaring class. From 3: Classes from Java Programming by Poornachandra Sarang Publisher: McGraw-Hill, Oracle Press Released: January 2012 Note 类中声明类。 Share this highlight http://www.safaribooksonline.com/a/java-programming/25511/ Twitter Facebook Google Plus Email Get Instant Access Now Start a Free Trial Learn about Safari for Business Have an account? Sign in. Minimise Unlock the rest of Java Programming and 30,000 other books and videos By clicking this box, you confirm that you have read and agree to the terms and conditions of our Membership Agreement, and you understand that when your trial period ends, you will be required to provide billing information if you wish to continue using the service. Unlock the rest of this book Start a Free 10-Day Trial loading Learn about Safari for Business Have an account? Sign in.