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) { ... } 
     ... 
  }