Interface Segregation Principle (ISP)

Overview

Clients should not be forced to depend on interfaces they don't use.

Many small, focused interfaces are better than one large "fat" interface. If an implementer must throw exceptions or provide no-ops for interface methods, the interface is too large.

When to Use

• Designing a new interface
• Implementing an interface with unused methods
• Forced to implement methods that don't apply
• Interface has more than 5-7 methods
• Different implementers use different subsets of methods

The Iron Rule