How to use SFDCCONTACTID in requestCampaign operation?

Have you checked the documentation/code samples at http://developers.marketo.com/documentation/soap/requestcampaign/?

If using Java, the code will look like this -

1. LeadKey key2 = new LeadKey();
2.             key2.setKeyType(LeadKeyRef.SFDCCONTACTID);
3.             key2.setKeyValue("0035000001sAYZm");

Thanks , I just don't how to check the diff  in marketo side.  You know that  contactis a object in SFDC.
But there is not a mobject named contact_record in marketo side . So  will the marketo merge those contact , account , lead of sfdc to marketo lead_record object?  And just give it one single foreign key named SFDCID?