Design Patterns Java™ Workbook

Chapter 8. Singleton

Objects can usually act responsibly just by performing their own work on their own attributes, without incurring obligations beyond self-consistency. Some objects, though, take on further responsibilities, such as modeling real-world entities, coordinating work, or modeling the overall state of a system. When a particular object in a system bears a responsibility on which other objects rely, you need a way of finding the responsible object. For example, you might need to find an object that represents a particular machine or a customer object that can construct itself from data in a database or an object that initiates system memory recovery.

When you need to find a responsible object, the object that you need will, in some ...