状态模式详解

解决的问题：无限的if elseif else

基本版：

package state;
 
public class V1 {
    public static void main(String[] args) {
        SayHi sayhi = new SayHi();
        sayhi.setTime(1);
        sayhi.doAction();
        sayhi.setTime(9);
        sayhi.doAction();
        sayhi.setTime(16);
        sayhi.doAction();
        sayhi.setTime(20);
        sayhi.doAction();
 
    }
}
 
//打招呼的类
class SayHi {
    Integer time;
 
    public Integer getTime() {
        return time;
    }
 
    public void setTime(Integer time) {
        this.time = time;
    }
 
    public void doAction() {
        if((time >= 0 && time < 4) ||  (time >= 19 && time <= 24)) {
            System.out.println("晚上好！");
        }else if(time >= 4 && time < 12) {
            System.out.println("上午好！");
        }else if(time >= 12 && time < 19) {
            System.out.println("下午好！");
        }
    }
}
 
 

状态模式版本：

package state;
 
public class V2 {
    public static void main(String[] args) {
        SayHi2 sayhi = new SayHi2();
        sayhi.setTime(1);
        sayhi.doAction();
        sayhi.setTime(9);
        sayhi.doAction();
        sayhi.setTime(16);
        sayhi.doAction();
        sayhi.setTime(20);
        sayhi.doAction();
    }
}
//环境类 也就是存放状态的类
class SayHi2 {
    private Integer time;
    private State state;
 
    public SayHi2() {
        state = new EveningState();
    }
 
    public State getState() {
        return state;
    }
 
    public void setState(State state) {
        this.state = state;
    }
 
    public Integer getTime() {
        return time;
    }
 
    public void setTime(Integer time) {
        this.time = time;
        this.setState(new EveningState());
    }
 
    public void doAction() {
        state.doAction(this);
    }
}
 
interface State {
    void doAction(SayHi2 sayHi2);
}
 
class EveningState implements State {
 
    @Override
    public void doAction(SayHi2 sayHi2) {
        if((sayHi2.getTime() >= 0 && sayHi2.getTime() < 4) ||  (sayHi2.getTime() >= 19 && sayHi2.getTime() <= 24)) {
            System.out.println("晚上好！");
        }else {
            sayHi2.setState(new MorningState());
            sayHi2.doAction();
        }
    }
}
 
class MorningState implements State {
 
    @Override
    public void doAction(SayHi2 sayHi2) {
        if(sayHi2.getTime() >= 4 && sayHi2.getTime() < 12) {
            System.out.println("上午好！");
        }else {
            sayHi2.setState(new AfternoonState());
            sayHi2.doAction();
        }
    }
}
 
class AfternoonState implements State {
 
    @Override
    public void doAction(SayHi2 sayHi2) {
        if(sayHi2.getTime() >= 12 && sayHi2.getTime() < 19) {
            System.out.println("下午好！");
        }else {
            System.out.println("我与您有时间差，不知道怎么向你打招呼");
        }
    }
}

状态接口uml图：