java23种设计模式-状态模式

定义

允许一个对象在其内部状态改变时改变它的行为，对象看起来似乎修改了它的类。状态模式是一种对象行为型模式。

角色

状态模式角色分类如下

• 抽象状态接口。定义状态的抽象行为。使用抽象类或者接口（interface）实现。
• 具体状态接口。实现了抽象状态。
• 环境类。聚合了一个状态引用，环境类可以根据环境的变化，动态改变状态引用所指向的具体状态对象。环境对象改变内部状态的特性，使该模式被定义为行为型设计模式。

UML

实现

以电热水器为例实现，热水器包括了加热和停止加热两个状态。

package design.patten.state;

/**
 * desc : 热水器状态接口
 * Created by tiantian on 2018/9/1
 */
public interface WaterHeaterState {

    void showTemperature();

    void setTemperature(int temperature);
}

/**
 * desc : 加热状态具体实现
 * Created by tiantian on 2018/9/1
 */
public class Heating implements WaterHeaterState {

    private int temperature;

    @Override
    public void showTemperature() {
        System.out.println(String.format("Water is heating and temperature is %d now", temperature));
    }

    public void setTemperature(int temperature) {
        this.temperature = temperature;
    }
}

/**
 * desc : 停止加热状态
 * Created by tiantian on 2018/9/1
 */
public class StopHeating implements WaterHeaterState{
    private int temperature;

    @Override
    public void showTemperature() {
        System.out.println(String.format("Water is heating and temperature is %d now", temperature));
    }

    public void setTemperature(int temperature) {
        this.temperature = temperature;
    }
}

/**
 * desc : 热水器（状态模式中的环境类）
 * Created by tiantian on 2018/9/1
 */
public class WaterHeater {
    private WaterHeaterState state;
    private int temperature = 0;

    public void open() { 
        setState(new Heating());
        Thread t = new Thread(() -> {
            while (true) {
                this.heating();
                state.setTemperature(temperature);
                try {
                    // 休眠若干时间，模拟加热过程
                    Thread.sleep(1000);
                    showTemper();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                if (temperature == 100) {
                    setState(new StopHeating());
                    System.out.println("Heating done! temperature is "+ temperature);
                    break;
                }
            }
        });
        t.start();
    }

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

    public WaterHeaterState getState() {
        return state;
    }

    public void heating() {
        temperature += 10;
    }

    public void showTemper() {
        state.showTemperature();
    }
}

/**
 * desc : 热水器测试
 * Created by tiantian on 2018/9/1
 */
public class WaterHeaterTest {
    public static void main(String[] args) throws InterruptedException {
        WaterHeater wh = new WaterHeater();
        wh.open();
    }
}
// output: 程序陆续输出如下
// Water is heating and temperature is 10 now
// Water is heating and temperature is 20 now
// Water is heating and temperature is 30 now
// Water is heating and temperature is 40 now
// Water is heating and temperature is 50 now
// Water is heating and temperature is 60 now
// Water is heating and temperature is 70 now
// Water is heating and temperature is 80 now
// Water is heating and temperature is 90 now
// Water is heating and temperature is 100 now
// Heating done! temperature is 100

总结

状态模式与策略模式及其相似，从UML结构也可以看出来。但两者又是有区别的。策略模式封装了若干算法族，让使用算法的用户自己选择具体的算法（策略)，用户要知晓具体算法的作用。而状态模式对用户完全透明，状态的转换完全由环境对象控制。