StarUML画InteractionOperation的方法：http://*.com/questions/16152278/using-alt-in-sequence-diagrams-for-staruml
I had just found the steps as following.Please refer how to set "alt combinedFragment at starUML due to I have no10 reputation to post image.
1.create a sequence diagram.
2.add a CombinedFragment1 into diagram.
3.change the "seq CombinedFragment1" to "alt CombinedFragment1 "
4.select the "InteractionOperand"
5.left-click at the "atlCombinedFragment1 ",you will found the one "InteractionOperand1"added into the "alt CombinedFragment1 ".
6.add the 2nd"InteractionOperand", same with step 4,step5, there will a partingline like the following.
7.set the InteractionOperand's Guarddata,my is "isInit",you will found it at the alt frame.
8.add the 2nd Guard data,same with thestep7.
9.move the diagram to the proper location.