Not only in Java , You have to use graph in every programming language as like as java. When you want to solve route based , map based or co-ordinate based problem , most of the time you need to use graph algorithms depends on problem.
Charts are utilized to speak to some genuine applications: Graphs are utilized to speak to systems. The systems may incorporate ways in a city or phone system or circuit organize. Diagrams are likewise utilized as a part of informal communities like linkedIn, Facebook. For instance, in Facebook, every individual is spoken to with a vertex(or hub).