状态模式

public interface State {
    public void doJob(Washing washing);
}

public class Start implements State {
    @Override
    public void doJob(Washing washing) {
        System.out.println("Start Washing Clothes!");
        washing.setState(new Work());
        washing.request();
    }
}

public class Work implements State{
    @Override
    public void doJob(Washing washing) {
        System.out.println("Working Now!");
        washing.setState(new End());
        washing.request();
    }
}

public class End implements State{
    @Override
    public void doJob(Washing washing) {
        System.out.println("All Finished!");
        washing.setState(null);
    }
}

public class Washing {
    private State state = null;
    
    public void setState(State state) {
        this.state = state;
        if (state == null) {
            System.out.println("Current state: null!");
        }
        else {
            System.out.println("Current state: " + state.getClass().getName());
        }
    }
    
    public void request() {
        if (state != null) {
            state.doJob(this);
        }
    }
}

public class Demo {
    public static void main(String[] args) {
        Washing washing = new Washing();
        washing.setState(new Start());
        washing.request();
    }
}

Current state: state.Start
Start Washing Clothes!
Current state: state.Work
Working Now!
Current state: state.End
All Finished!
Current state: null!