Sybex Java OCP 8 Study Guide Chapter 1 page 63 small typo
It's an example about polymorphism.
Lemur lemur = new Lemur();
HasTail hasTail = lemur;
System.out.println(hasTail.age);// DOES NOT COMPILE
Typo: In this example, the reference hasTail has direct access only to methods defined "with" the HasTail interface;
Also on page 94 in the last paragraph.
The singleton and immutable object patterns are both types of creational patterns, which are design patterns that facilitate the creation of objects WITH an application.