Command Pattern

Command becomes useful when “do this action” should itself become a first-class object.

In Java, that matters when requests need capabilities beyond direct method calls:

• queuing
• retrying
• scheduling
• auditing
• undo and redo

The pattern is strongest when command objects carry meaningful intent and lifecycle. It is weakest when a plain method call is wrapped only because a catalog said to do so.

In this section

• Implementing Command in Java
  Implement Command in Java by separating request intent from invocation timing and receiver details.
• Invoker, Command, and Receiver Roles
  Distinguish the Command roles in Java so request creation, request invocation, and actual work execution stay properly separated.
• Implementing Undo and Redo with the Command Pattern
  Use Command for undo and redo in Java when reversible intent and command history are worth modeling explicitly.
• Command Pattern in Multithreading
  Use Command in Java multithreaded systems when work items must cross thread boundaries cleanly, but keep thread safety and retry semantics explicit.
• Command Pattern Use Cases and Examples in Java
  See where Command genuinely helps in Java systems, from UI actions and job queues to undo stacks, schedulers, and audit trails.