设计模式（命令模式）

命令行把请求和操作封装起来，坦白的讲，我现在还不是特别理解，也没有再具体的项目中使用过，感觉有点过于复杂。

本文参考一些材料，给出一个简单的例子。如下：

• Trade

public class Trade {
    public void doSell(){
        System.out.println("doSell");
    }

    public void doBuy(){
        System.out.println("doBuy");
    }
}

• TradeCommand

public abstract class TradeCommand {
    protected Trade trade;

    public TradeCommand(Trade trade){
        this.trade = trade;
    }

    public abstract void execute();
}

• BuyTradeCommand

public class BuyTradeCommand extends TradeCommand {

    public BuyTradeCommand(Trade trade) {
        super(trade);
    }

    @Override
    public void execute() {
        this.trade.doBuy();
    }
}

• SellTradeCommand

public class SellTradeCommand extends TradeCommand {

    public SellTradeCommand(Trade trade) {
        super(trade);
    }

    @Override
    public void execute() {
        this.trade.doSell();
    }
}

• Invoke

public class Invoke {
    public TradeCommand command;

    public void setCommand(TradeCommand command){
        this.command = command;
    }

    public void execute(){
        command.execute();
    }
}

• APP 测试类

public class App {

    public static void main(String[] args) {
        Trade trade = new Trade();
        Invoke invoke = new Invoke();
        invoke.setCommand(new SellTradeCommand(trade));
        invoke.execute();
        invoke.setCommand(new BuyTradeCommand(trade));
        invoke.execute();
    }
}