For every time you insert a key-value pair in HashMap , If the key is repeated ,it will replace the previous value with the current one. But if you really need to know more , make use of TreeSet, ArrayList, Vector combinations along with this. Try out all the methods availble in these and learn what you can do more. Understanding the basic requirement where Maps are needed will definetely help you. Just try it out.
"Learning is a Culture where your Eagerness & Curiosity plays a major Role".