WebParam.Mode.OUT meaning and documentation

Question

I usually create stub to interrogate external web service, It is the first time that after I created the stub of a project, in the Service.class I have this code:

public void getInformation(
    @WebParam(name = "username", targetNamespace = "http://mysite")
    java.lang.String username,
    @WebParam(name = "password", targetNamespace = "http://mysite")
    java.lang.String password,
    @WebParam(mode = WebParam.Mode.OUT, name = "GetInformation", targetNamespace = "http://mysite")
    javax.xml.ws.Holder<MyInformation> getInformation,
    @WebParam(mode = WebParam.Mode.OUT, name = "outPut", targetNamespace = "http://mysite")
    javax.xml.ws.Holder<MyFile> fOutPut
);

In the documentation of this web method there is written that the input parameter is username and password, and the output parameter is Holder getInformation,Holder fOutPut; but when I try to call the method, I have to insert all the paramenter in input, like myClientClass.getInformation(username,password,getInformation,fOutPut);

I try to search online a documentation but I have not found anything, I have understand that It is a way to populate my output value without have It in return, but I want to understand how It really works and If there is any documentation/example to implement a web method like this or how to send value in this way. Thank you