State vs. Strategy Pattern

State and Strategy often look similar because both delegate behavior through an interface. The difference is why the behavior changes.

Strategy

Behavior changes because:

• the caller chooses an algorithm
• configuration selects a policy
• the system wants interchangeable behaviors

State

Behavior changes because:

• the object is now in a different lifecycle state
• the meaning of an operation depends on current internal status

Java Shortcut

Ask:

• “Who chooses the behavior?” If it is the caller or configuration, think Strategy.
• “What changed inside the object?” If it is lifecycle or status, think State.

They can share structure, but they solve different runtime problems.