java如何实现状态机

在Java中实现状态机可以通过以下几种方法：

1. 使用枚举和接口：

public enum State {
    STATE_A, STATE_B, STATE_C;
}

public interface StateMachine {
    void setState(State state);
    State getState();
    void onEntry(State state);
    void onExit(State state);
}

public class MyStateMachine implements StateMachine {
    private State state;

    @Override
    public void setState(State state) {
        this.state = state;
        onExit(this.state);
        onEntry(state);
    }

    @Override
    public State getState() {
        return state;
    }

    @Override
    public void onEntry(State state) {
        // 处理进入状态的逻辑
    }

    @Override
    public void onExit(State state) {
        // 处理退出状态的逻辑
    }
}

2. 使用状态模式：

public interface State {
    void handle(Context context);
}

public class StateA implements State {
    @Override
    public void handle(Context context) {
        // 处理StateA的逻辑
        context.setState(new StateB());
    }
}

public class StateB implements State {
    @Override
    public void handle(Context context) {
        // 处理StateB的逻辑
        context.setState(new StateC());
    }
}

public class StateC implements State {
    @Override
    public void handle(Context context) {
        // 处理StateC的逻辑
        context.setState(new StateA());
    }
}

public class Context {
    private State state;

    public Context() {
        state = new StateA();
    }

    public void setState(State state) {
        this.state = state;
    }

    public void request() {
        state.handle(this);
    }
}

3. 使用第三方库，如Apache Commons State或状态机库（如：jsr310-state）：

Apache Commons State: https://commons.apache.org/proper/commons-state/

JSR 310 State: https://www.jcp.org/en/jsr/detail?id=310

这些方法都可以实现状态机，你可以根据项目需求选择合适的方法。