Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.
Participants
- Context: defines the interface of interest to clients Maintains an instance of a ConcreteState subclass that defines the current state.
- State: defines an interface for encapsulating the behavior associated with a particular state of the Context.
- Concrete State: each subclass implements a behavior associated with a state of Context
Code
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public class Main { public static void main(String[] args) { Context c = new Context(new ConcreteStateA()); c.request(); c.request(); c.request(); c.request(); }}public interface State { void handle(Context context);}public class ConcreteStateA implements State { @Override public void handle(Context context) { context.setState(new ConcreteStateB()); }}public class ConcreteStateB implements State { @Override public void handle(Context context) { context.setState(new ConcreteStateA()); }}public class Context { private State state; public Context(State state) { setState(state); } public State getState() { return state; } public void setState(State state) { this.state = state; System.out.println("State: " + state.getClass().getSimpleName()); } public void request() { state.handle(this); }} |
Output
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State: ConcreteStateAState: ConcreteStateBState: ConcreteStateAState: ConcreteStateBState: ConcreteStateA |
eidherjulian61 / design-patterns
| Published on Java Code Geeks with permission by Eidher Julian, partner at our JCG program. See the original article here: State Pattern
Opinions expressed by Java Code Geeks contributors are their own. |
