状态模式（State），当一个对象的内在状态改变时允许改变其行为，这个对象看起来像是改变了其类。代替大量if else if判断分支条件。
PS：其实就通过子类的各种继承来进行逻辑转换，通过定义新的子类可以很容易地增加新的状态和转换。
当一个对象的行为取决于它的状态，并且它必须在运行时刻根据状态改变它的行为时，就可以考虑使用状态模式

主方法

public class main {
    public static void main(String[] args) {
        Work emergencyProjects = new Work();
        emergencyProjects.setHour(9);
        emergencyProjects.writeProgram();
        emergencyProjects.setHour(10);
        emergencyProjects.writeProgram();
        emergencyProjects.setHour(12);
        emergencyProjects.writeProgram();
        emergencyProjects.setHour(13);
        emergencyProjects.writeProgram();
        emergencyProjects.setHour(14);
        emergencyProjects.writeProgram();
        emergencyProjects.setHour(17);

        emergencyProjects.setFinish(true);
//        emergencyProjects.setFinish(false);

        emergencyProjects.writeProgram();
        emergencyProjects.setHour(19);
        emergencyProjects.writeProgram();
        emergencyProjects.setHour(22);
        emergencyProjects.writeProgram();
    }
}

状态抽象类

/**
 * 抽象状态类
 */
public abstract class State {
    public abstract void writeProgram(Work work);
}

工作类

/**
 * 工作类
 */
public class Work {
    public Work() {
        current = new ForenoonState();
    }

    private State current;
    private int hour;//时间属性，状态转换的依据
    private boolean finish = false;//工作任务是否完成的标志位

    public void writeProgram() {
        current.writeProgram(this);
    }

    public State getCurrent() {
        return current;
    }

    public void setCurrent(State current) {
        this.current = current;
    }

    public int getHour() {
        return hour;
    }

    public void setHour(int hour) {
        this.hour = hour;
    }

    public boolean isFinish() {
        return finish;
    }

    public void setFinish(boolean finish) {
        this.finish = finish;
    }
}

多种状态类

public class ForenoonState extends State {
    public void writeProgram(Work work) {
        if (work.getHour() < 12) {
            System.out.println(String.format("当前时间：{%d}点 上午工作，精神百倍", work.getHour()));
        } else {
            work.setCurrent(new NoonState());
            work.writeProgram();
        }
    }
}

public class NoonState extends State {
    public void writeProgram(Work work) {
        if (work.getHour() < 13) {
            System.out.println(String.format("当前时间：{%d}点 饿了，午饭；犯困，午休。", work.getHour()));
        } else {
            work.setCurrent(new AfternoonState());
            work.writeProgram();
        }
    }
}

public class AfternoonState extends State {
    public void writeProgram(Work work) {
        if (work.getHour() < 17) {
            System.out.println(String.format("当前时间：{%d}点 下午状态还不错，继续努力", work.getHour()));
        } else {
            work.setCurrent(new EveningState());
            work.writeProgram();
        }
    }
}

/**
 * 加个finish判断，如果任务完成即下班
 */
public class EveningState extends State {
    public void writeProgram(Work work) {
        if (work.isFinish()) {//如果工作完成了就调用下班休息类
            work.setCurrent(new RestState());
            work.writeProgram();
        } else {
            if (work.getHour() < 21) {
                System.out.println(String.format("当前时间：{%d}点 加班哦，疲累之极", work.getHour()));
            } else {
                work.setCurrent(new SleepingState());//工作未完成
                work.writeProgram();
            }
        }
    }
}

public class RestState extends State {
    public void writeProgram(Work work) {
        System.out.println(String.format("当前时间：{%d}点 下班回家了", work.getHour()));
    }
}

public class SleepingState extends State {
    public void writeProgram(Work work) {
        System.out.println(String.format("当前时间：{%d}点 不行了，睡着了", work.getHour()));
    }
}