行为型模式-状态

结构图






客户端

public static void main(String[] args) {
		// 设置Context的初始状态为ConcreteStateA
		Context ctx = new Context(new ConcreteStateA());
		ctx.request();
		ctx.request();
		ctx.request();
		ctx.request();
}

类设计

public interface State {
	public void handle(Context context);
}
public class Context {
	private State state;


	public Context(State state) {
		this.state = state;
	}


	public State getState() {
		return state;
	}


	public void setState(State state) {
		this.state = state;
	}


	public void request() {
		state.handle(this);
	}
}
public class ConcreteStateA implements State {


	@Override
	public void handle(Context context) {
		System.out.println("change state to B");
		context.setState(new ConcreteStateB());
	}


}
public class ConcreteStateB implements State {


	@Override
	public void handle(Context context) {
		System.out.println("change state to A");
		context.setState(new ConcreteStateA());
	}


}