i have read wiki for quite a while but still not clear about that and this is my code,can someone please tell me where is bug
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private IOrder submitOrder(OrderCommand orderCmd) throws JFException {
        long goodTillTime =  System.currentTimeMillis() + 60*1000*15*30;
        double stopLossPrice, takeProfitPrice;
        double k=0;
        for (int i=1;i<=55;i++) 
         
        {
         double Bar_length=history.getBar(instrument, selectedPeriod, OfferSide.BID, i).getHigh()-history.getBar(instrument, selectedPeriod, OfferSide.BID, i).getLow();
         k=k+Bar_length;
         }
         k=k/27;
        // Calculating stop loss and take profit prices
        if (orderCmd == OrderCommand.PLACE_BID) {
            stopLossPrice = history.getLastTick(this.instrument).getBid() - getPipPrice(this.stopLossPips)-k;
            takeProfitPrice = history.getLastTick(this.instrument).getBid() + getPipPrice(this.takeProfitPips);
            console.getOut().println(k);
    return engine.submitOrder(getLabel(instrument), this.instrument, orderCmd, this.amount, history.getLastTick(this.instrument).getBid()-k, 2, stopLossPrice, takeProfitPrice,goodTillTime);  //this one really submit orders!!!
        } 
        if (orderCmd == OrderCommand.PLACE_OFFER){
            stopLossPrice = history.getLastTick(this.instrument).getAsk() + getPipPrice(this.stopLossPips)+k;
            takeProfitPrice = history.getLastTick(this.instrument).getAsk() - getPipPrice(this.takeProfitPips);
            console.getOut().println(k);
    return engine.submitOrder(getLabel(instrument), this.instrument, orderCmd, this.amount, history.getLastTick(this.instrument).getBid()+k, 2, stopLossPrice, takeProfitPrice,goodTillTime);  //this one really submit orders!!!
        }

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after compiled ,error message is : This method must return a result of type IOrder

all execution paths of the method need to return an IOrder object. Adding return null should solve the compilation problem, however, you need to check if this is correct from you strategy logic perspective.
In order to avoid such compile-time errors, consider using an IDE, e.g. Eclipse or NetBeans.