设计模式—行为型模式之状态模式

本文介绍: 本文介绍了行为型设计模式中的状态模式，讲解了它的特点和相关构成，并结合案例使用Java代码进行演示。

状态（State）模式：对有状态的对象，把复杂的“判断逻辑”提取到不同的状态对象中，允许状态对象在其内部状态发生改变时改变其行为。

状态模式包含以下主要角色：

比如我们的会议有以下状态：待创建、待开始、进行中、已结束状态；我们的代码如下：

/**
 * 状态接口
 */
public interface MeetingStateInterface {
    //当前状态
    void state();

    //下一个状态
    MeetingStateInterface next();
}

public class WaitCreateMeetingState implements MeetingStateInterface{
    @Override
    public void state() {
        System.out.println("当前在待创建状态");
    }

    @Override
    public MeetingStateInterface next() {
        return new WaitStartMeetingState();
    }
}

public class WaitStartMeetingState implements MeetingStateInterface{
    @Override
    public void state() {
        System.out.println("待开始状态");
    }

    @Override
    public MeetingStateInterface next() {
        return new ProcessingMeetingState();
    }
}

public class ProcessingMeetingState implements MeetingStateInterface{
    @Override
    public void state() {
        System.out.println("会议进行中状态");
    }

    @Override
    public MeetingStateInterface next() {
        return new EndMeetingState();
    }
}

public class EndMeetingState implements MeetingStateInterface{
    @Override
    public void state() {
        System.out.println("已结束会议状态");
    }

    @Override
    public MeetingStateInterface next() {
        return null;
    }
}

会议类如下：

public class Meeting {
    
    private MeetingStateInterface meetingState;

    public void setMeetingState(MeetingStateInterface meetingState) {
        this.meetingState = meetingState;
    }
    
    //会议当前状态
    public void state(){
        meetingState.state();
    }
    
    //下一个状态
    public void nextState(){
        if(this.meetingState != null){
			this.meetingState = this.meetingState.next();
        }
    }
}

public class StateTest {
    public static void main(String[] args) {
        Meeting meeting = new Meeting();
        meeting.setMeetingState(new WaitCreateMeetingState());
        meeting.state();
        meeting.nextState();
        meeting.state();
        meeting.nextState();
        meeting.state();
        meeting.nextState();
        meeting.state();
        meeting.nextState();
    }
}