菜鸟硕枫设计模式系列之21 状态模式

避免了复杂的条件；取而代之以状态对象。优势在于允许对象改变内部状态。和策略优势有很多相似之处。状态模式也是一种行为模式。

状态模式类图：
                               


具体代码示例：

package statePattern;

public interface State {

	void handle(Object a);
	State changeState();
}

package statePattern;

public class ConcreteStateA implements State{

	@Override
	public void handle(Object a) {
		System.out.println("hello,it's ConcreteStateA object working");
	}

	@Override
	public State changeState() {
		// TODO Auto-generated method stub
		return new ConcreteStateB();
	}

}

package statePattern;

public class ConcreteStateB implements State{

	@Override
	public void handle(Object a) {
		System.out.println("hello,it's ConcreteStateB object working");
	}

	@Override
	public State changeState() {
		// TODO Auto-generated method stub
		return new ConcreteStateA();
	}

}

package statePattern;

public class Context {

	private State state;

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

}

package statePattern;

public class testStatePattern {

	public static void main(String[]args){
		Context context = new Context();
		State concreteState = new ConcreteStateA();
		context.setState(concreteState);
		//起始状态
		context.doSomething();
		//对象改变自身状态之后
		context.doSomething();
	}
}