OPT.INSOF

Test "instanceof" to an interface

Description

This rule flags code that performs "instanceof" tests to a class rather than to an interface.

Because interface-based design allows for the flexible inclusion of different implementations, it is generally beneficial. Whenever possible, perform "instanceof" tests to an interface rather than a class.

Example

 package OPT;
 
 public class INSOF {
     private void method (Object o) {
         if (o instanceof InterfaceBase) { }  // better
         if (o instanceof ClassBase) { }   // worse.
     }
 }
 
 class ClassBase {}
 interface InterfaceBase {}

Reference

Graig Larman, Rhett Guthrie. Java 2 Performance and Idiom Guide. Prentice Hall, 2000, p.207.