java - Is this a valid case to use instanceof operator? -

i beginner in java , oop in general, , have question regarding inheritance in java.

in project, have class order represents order placed asset. intend have several classes extend order including limitbuyorder , limitsellorder & likewise market orders.

i have class position, consists of pair of orders. in order determine kind of position, must know type of order entered first. although instanceof operator work in situation, feel not appropriate solution. below stripped-down snippet, may illustrate problem:

class position {     //other fields , methods omitted clarity     public void open(order o) {         if(o instanceof limitbuyorder)             //set position type long         if(o instanceof limitsellorder)             //set position type short     } } 

or should define methods in order such islimitbuy() & etc, return false , override them return true based on subclass order extended by?

class position {     //other fields , methods omitted clarity     public void open(order o) {         if(o.islimitbuyorder())             //set position type long         if(o.islimitsellorder())             //set position type short     } } 

basically, question how determine type of subclass properly? in advance!

you should aim encapsulate behaviour within types of orders rather using types externally switch behaviour.

add method 'order' class work , not have know type @ all:

order.openposition(...); 

let 'order' whatever needs according type.

a significant benefit encapsulation end having order-type-specific behaviour in 1 place. abstract parent classes come naturally provide common order characteristics. code in 1 place (or @ least in small hierarchy of classes) can change behaviour without having visit code on application.