HI EVERYONE!!In applets how to take coordinates as input given by user.Also we dont know number of coordinates user enters .In simple,how to take several points as input and present them on a graph as output??

First you need to tell more why you used the word "applets" since you could mean you want a web browser to run this. If so you have an embarrassment of riches to pick from for plotting. Example? https://www.google.com/#q=online+java+data+plotter

As to collecting the items into your array, that's something you should have been coding before you tackle a plotting system. So break that off into it's own piece of work.