Java generics casting

Question

How please works following generic casting?

private <T, N> N send(final T request) {
    final String serviceUrl = "someUri"

    try {
        return (N) webServiceTemplate.marshalSendAndReceive(serviceUrl, request);
    } catch (final SoapFaultClientException e) {

    }
}

When I call this private method like this:

MyReq request = new  MyReq();
MyResp response = send(req);

How this method casting this object into MyResp object? What mean this in return type:

< T, N>

<T, N> means, that the method has two type parameters, named T and N. — Smutje
– Smutje, Commented Aug 5, 2014 at 6:35
your return type is only N. <T, N> is a kind of initialization of the generic variables. This is the syntax of generic variables initialization. — Mustafa Celik
– Mustafa Celik, Commented Aug 5, 2014 at 6:39

Konstantin Yovkov · Accepted Answer · 2014-08-05 09:20:21Z

1

< T, N>

Is not a return type. N is.

private <T, N> N send(final T request)
               ↑

You have "choosen" type T by passing MyReq argument. Before returning value of marshalSendAndReceive it is being casted to N type. In your case MyResp.

<T,N>

just declares that this class/method is generic and you may specify generic input type as well ans output.

edited Aug 5, 2014 at 9:20

Konstantin Yovkov

63k9 gold badges107 silver badges152 bronze badges

answered Aug 5, 2014 at 6:37

locohamster

1176 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

user1089362 Over a year ago

Ok, so (N) webServiceTemplate.marshalSendAndReceive just casting object into N (MyResp) ok? And why I can't just return N object? Why I need there <T,N> ?

locohamster Over a year ago

<T,N> allows you to use send method with any T argument type and expect N type of returned value from the method. Consider N and T as "variables" that will be initialized when constructing class/using method. The same method might get String input and return Integer output. But in your case it received MyReq and returns MyResp. That's the point of generics in Java.

locohamster Over a year ago

Non-generic version of this method would be:

private MyResp send(final MyReq request) {     final String serviceUrl = "someUri"      try {         return (MyReq) webServiceTemplate.marshalSendAndReceive(serviceUrl, request);     } catch (final SoapFaultClientException e) {      } }

locohamster Over a year ago

semi-generic:

private <Z> Z send(final MyReq request) {     final String serviceUrl = "someUri"      try {         return (Z) webServiceTemplate.marshalSendAndReceive(serviceUrl, request);     } catch (final SoapFaultClientException e) {      } }

Now it may return any type marked as Z while it can get MyReq as input.

merlin2011 · Accepted Answer · 2014-08-05 06:36:30Z

0

The method is parameterized with the generic parameters T and N. It takes an argument of type T and returns a reference of type N.

The return type is not <T,N>, it is just N.

answered Aug 5, 2014 at 6:36

merlin2011

76.5k49 gold badges218 silver badges364 bronze badges

Comments

Nabin · Accepted Answer · 2014-08-05 06:37:58Z

0

It's about using templates in java similar to templates in C++;

Example:

void add(T x, T y){
System.out.println(x+y);
}

Above function can be called with either of the following...

add(3.0f, 4.5f);
add(2,3);

Means, the function is for any kind of parameters

answered Aug 5, 2014 at 6:37

Nabin

11.8k8 gold badges70 silver badges103 bronze badges

Comments

Deepanshu J bedi · Accepted Answer · 2014-08-05 06:59:49Z

0

Here T and N are Generic parameters.

Here the return type is N not <T,N>.

Collectives™ on Stack Overflow

Java generics casting

4 Answers 4

4 Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

4 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related