Editing State pattern (section)

== Structure ==
[[File:State Design Pattern UML Class Diagram.svg|thumb|right|400px|State in UML<ref name="GOF" />]]
In the accompanying [[Unified Modeling Language]] (UML) [[class diagram]], the <code>Context</code> class doesn't implement state-specific behavior directly. Instead, <code>Context</code> refers to the <code>State</code> interface for performing state-specific behavior (<code>state.handle()</code>), which makes <code>Context</code> independent of how state-specific behavior is implemented. The <code>ConcreteStateA</code> and <code>ConcreteStateB</code> classes implement the <code>State</code> interface, that is, implement (encapsulate) the state-specific behavior for each state. The UML [[sequence diagram]] shows the run-time interactions:

The <code>Context</code> object delegates state-specific behavior to different <code>State</code> objects. First, <code>Context</code> calls <code>handle(this)</code> on its current (initial) state object (<code>ConcreteStateA</code>), which performs the operation and calls <code>setState(ConcreteStateB)</code> on <code>Context</code> to change context's current state to <code>ConcreteStateB</code>. The next time, <code>Context</code> again calls <code>handle(this)</code> on its current state object (<code>ConcreteStateB</code>), which performs the operation and changes context's current state to <code>ConcreteStateA</code>.