SE450: Horstmann Chapter 3: Cohesion

Class describes a single abstraction
Methods should be related to the single abstraction

Bad example:

public class Mailbox 
{ 
   public addMessage(Message aMessage) { ... } 
   public Message getCurrentMessage() { ... } 
   public Message removeCurrentMessage() { ... } 
   public void processCommand(String command) { ... } 
   ... 
}