狀態模式是行為模式的一種，狀態模式允許改變物件內部狀態來改變物件的行為。

角色和職責：

1.上下文（Context）-Order：

   擁有內部的狀態

2.狀態介面（Status）-State:

    一個所有具體狀態的共同介面；任何狀態都實現這個相同的介面，這樣一來狀態之間可以互相替換

3.具體狀態（Concrete State）-:

UML圖：

具體原始碼：

/**
 * 狀態介面類
 */
public abstract class State {
    
 
protected int owner_order_status = 0;//當前狀態物件的具體狀態
    protected State next_state;//當前狀態的下一個狀態
    public State(int owner_order_status,State next_state){
        this.owner_order_status = owner_order_status;
        this.next_state = next_state;
    }

    /**
     * 處理
     * @param orderStatus
     */
    protected
 
  void handler(int orderStatus){
        if(!isOwner(owner_order_status,orderStatus)){
            if(next_state != null){
                //非當前物件，繼續到下一個物件中查詢
                next_state.handler(orderStatus);
                return;
            }
            System.out.println("當前訂單狀態未定義");
            
 
return;
        }
        diaplay();
    }

    /**
     * 是否當前物件
     * @return
     */
    public boolean isOwner(int owner_order_status,int orderStatus){
        if(owner_order_status == orderStatus){
            return true;
        }
        return false;
    }

    abstract void diaplay();
}

/**
 * 訂單建立
 */
public class OrderCreateState extends State
{
    public OrderCreateState(int owner_order_status, State next_state) {
        super(owner_order_status, next_state);
    }

    @Override
    void diaplay() {
        System.out.println("訂單建立");
    }
}

/**
 * 訂單支付
 */
public class OrderPayState extends State {

    public OrderPayState(int owner_order_status, State next_state) {
        super(owner_order_status, next_state);
    }

    @Override
    void diaplay() {
        System.out.println("訂單支付");
    }
}

/**
 * 訂單完成
 */
public class OrderSuccessState extends State{
    public OrderSuccessState(int owner_order_status, State next_state) {
        super(owner_order_status, next_state);
    }

    @Override
    void diaplay() {
        System.out.println("訂單完成");
    }
}

/**
 * 訂單狀態關閉
 */
public class OrderCloseState extends State{
    public OrderCloseState(int owner_order_status, State next_state) {
        super(owner_order_status, next_state);
    }

    @Override
    void diaplay() {
        System.out.println("訂單狀態關閉");
    }
}

/**
 * 訂單
 */
public class Order {
    private State orderState;
    public Order(){
        orderState = new OrderCreateState(1,
                new OrderPayState(2,
                        new OrderSuccessState(3,
                                new OrderPayState(4,null))));
    }

    public State getOrderState() {
        return orderState;
    }
}

public class Main {
    public static void main(String[] args) {
        Order order = new Order();
        State orderState = order.getOrderState();
        orderState.handler(1);//訂單建立
        orderState.handler(2);//訂單支付
        orderState.handler(3);//訂單完成
        orderState.handler(4);//訂單關閉
        orderState.handler(5);//訂單未定義
    }
}

結果：

訂單建立
訂單支付
訂單完成
訂單支付
當前訂單狀態未定義

原始碼地址：https://github.com/qjm201000/design_pattern_state.git