大话设计模式——17.状态模式（State Pattern）

简介

对象的行为依赖于它的状态（属性），可以根据状态的改变而改变相关行为。

UML图：

在这里插入图片描述

应用场景：

对象的行为取决于其状态，并且必须要在运行时刻根据状态而改变行为
代码中包含大量与对象状态有关的条件语句

示例

上午、下午、晚上工作的状态

上下文对象：

public class Work {/*** 工作状态*/private State state;/*** 当前时间*/private int hour;/*** 工作是否完成*/private boolean isFinished;public Work() {// 初始化操作this.state = new MorningState();}public void writeProgram() {state.writeProgram(this);}public State getState() {return state;}public void setState(State state) {this.state = state;}public int getHour() {return hour;}public void setHour(int hour) {this.hour = hour;}public boolean isFinished() {return isFinished;}public void setFinished(boolean finished) {isFinished = finished;}
}

状态

public interface State {void writeProgram(Work work);
}

public class MorningState implements State {@Overridepublic void writeProgram(Work work) {if (work.getHour() < 12) {System.out.println("当前时间：" + work.getHour() + "，干劲十足！");} else {work.setState(new NoonState());work.writeProgram();}}
}

public class NoonState implements State {@Overridepublic void writeProgram(Work work) {if (work.getHour() < 13) {System.out.println("当前时间：" + work.getHour() + "，好饿，开始干饭!");} else {work.setState(new AfternoonState());work.writeProgram();}}
}

public class AfternoonState implements State {@Overridepublic void writeProgram(Work work) {if (work.getHour() < 18) {System.out.println("当前时间：" + work.getHour() + "，开始上班，有点疲惫！");} else {work.setState(new EveningState());work.writeProgram();}}
}

public class EveningState implements State {@Overridepublic void writeProgram(Work work) {if (!work.isFinished()) {System.out.println("当前时间：" + work.getHour() + "，又要加班");} else {System.out.println("当前时间：" + work.getHour() + "，下班啦！");}}
}

运行

public class Main {public static void main(String[] args) {Work work = new Work();// 上午work.setHour(9);work.writeProgram();// 中午work.setHour(12);work.writeProgram();// 下午work.setHour(16);work.writeProgram();// 晚上work.setHour(18);
//        work.setFinished(true);work.writeProgram();}
}