hi Indu, what ever i know regarding vector,set and Map. to my knowlede, hope so they are almost correct. vector - this is class implementing from list interface,and can increase size dynamically ,this is safe in use of threads as it supports for synchronization.this will give U in order(not soreted).allows duplicate of elements. Set is an interface extending from Collection interface,doesnot allow duplicacy of elements.and this was not ordered.(it allow a null value i think this is not sure). Map is an interface ,which has both keys and values . keys are not allowed for duplication,but values are allowed. (null key and null value are allowed i think ).this is not ordered.but this is mainly used for fast retrival of data. hope this can understand u, a litle more knowledge is reqired that is also i was looking for. for a specific key U get corresponding value.