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Question

我想知道您认为哪一个设计更好。假设我们有

/*
* Created 21 Feb 2014
*/


import java.util.Properties;
import java.util.Random;

/**
*
* @author me
*/

enum EventType{
    TRADE, RISK, SHIPPING, MARGIN, STOP_LOSS, TAKE_PROFIT
}

interface Event{
    EventType getType();
    Properties getProperties();
}


class ShippingEvent implements Event{
    public final static String PROPERTY_KEY1 = "property_ke1";
    public final static String PROPERTY_KEY2 = "property_ke2";
    public final static String PROPERTY_KEY3 = "property_ke3";

    @Override
    public EventType getType() {
        return EventType.SHIPPING;
    }

    @Override
    public Properties getProperties() {
        throw new UnsupportedOperationException("Not supported yet.");
    }
}


class TradeEvent implements Event{
    public final static String PROPERTY_KEY1 = "property_ke1";
    public final static String PROPERTY_KEY2 = "property_ke2";
    public final static String PROPERTY_KEY3 = "property_ke3";

    @Override
    public EventType getType() {
        return EventType.TRADE;
    }

    @Override
    public Properties getProperties() {
        throw new UnsupportedOperationException("Not supported yet.");
    }
}

class RiskEvent implements Event{
    public final static String PROPERTY_KEY1 = "property_ke1";
    public final static String PROPERTY_KEY2 = "property_ke2";
    public final static String PROPERTY_KEY3 = "property_ke3";

    @Override
    public EventType getType() {
        return EventType.RISK;
    }

    @Override
    public Properties getProperties() {
        throw new UnsupportedOperationException("Not supported yet.");
    }
}

class MarginEvent implements Event{
    public final static String PROPERTY_KEY1 = "property_ke1";
    public final static String PROPERTY_KEY2 = "property_ke2";
    public final static String PROPERTY_KEY3 = "property_ke3";

    @Override
    public EventType getType() {
        return EventType.MARGIN;
    }

    @Override
    public Properties getProperties() {
        throw new UnsupportedOperationException("Not supported yet.");
    }
}

class StopLossEvent implements Event{
    public final static String PROPERTY_KEY1 = "property_ke1";
    public final static String PROPERTY_KEY2 = "property_ke2";
    public final static String PROPERTY_KEY3 = "property_ke3";

    @Override
    public EventType getType() {
        return EventType.STOP_LOSS;
    }

    @Override
    public Properties getProperties() {
        throw new UnsupportedOperationException("Not supported yet.");
    }
}

class TakeProfiEvent implements Event{
    public final static String PROPERTY_KEY1 = "property_ke1";
    public final static String PROPERTY_KEY2 = "property_ke2";
    public final static String PROPERTY_KEY3 = "property_ke3";

    @Override
    public EventType getType() {
        return EventType.TAKE_PROFIT;
    }

    @Override
    public Properties getProperties() {
        throw new UnsupportedOperationException("Not supported yet.");
    }
}

public class InstanceOfTest {

    private static void testIfBranch(final Event event){
        if (event instanceof TakeProfiEvent){
            System.out.println("TakeProfiEvent");
        }else if (event instanceof StopLossEvent){
            System.out.println("StopLossEvent");
        }else if (event instanceof MarginEvent){
            System.out.println("MarginEvent");
        }else if (event instanceof RiskEvent){
            System.out.println("RiskEvent");
        }else if (event instanceof TradeEvent){
            System.out.println("TradeEvent");
        }else if (event instanceof ShippingEvent){
            System.out.println("ShippingEvent");
        }
    }




    private static void testSwitchBranch(final Event event){

        switch(event.getType()){
            case TRADE:
                System.out.println("TradeEvent");
                break;
            case RISK:
                System.out.println("RiskEvent");
                break;
            case SHIPPING:
                System.out.println("ShippingEvent");
                break;
            case MARGIN:
                System.out.println("MarginEvent");
                break;
            case STOP_LOSS:
                System.out.println("StopLossEvent");
                break;
            case TAKE_PROFIT:
                System.out.println("TakeProfiEvent");    
                break;
            default:
                break;
        }
    }

    public static void main(String[] args){
        Event[] events = new Event[] {
            new TakeProfiEvent(),
            new StopLossEvent(),
            new MarginEvent(),
            new RiskEvent(),
            new TradeEvent(),
            new ShippingEvent()
        };


        Random random = new Random(System.currentTimeMillis());
        long start = System.currentTimeMillis();
        for(int idx=0; idx<10000000; ++idx){
            int jdx = random.nextInt(events.length-1);
            //testIfBranch(events[jdx]);
            testSwitchBranch(events[jdx]);
        }
        long end = System.currentTimeMillis();

        System.out.println("Time taken: " + (end - start));
    }

}

我进行的测试表明 switch 语句对于所有测试用例都表现得更好，正如 Compiling switch in the JVM 所预期的那样。 。另外，我倾向于不使用 instanceof 运算符，因为我发现在这种情况下它会使扩展软件变得困难。例如，我使用 getType() 方法，我可以轻松使用 IoC 或 DI。另外，我认为使用 instanceof 运算符会创建对类定义的明确依赖。我想听听您对此的想法，特别是在软件工程方面 - 陷阱和/或最佳实践。

结果示例:

Switch Branch: 304916ms
If Branch: 307924ms

Answer 1

毫无疑问，最好的设计是开关设计。有关最佳实践，请参阅 http://www.javapractices.com/topic/TopicAction.do?Id=31