Hi, could anybody explain what Vertex and AdaptablePriorityQueue is in this exmaple? or where I can find more information about it? I belive that AdaptablePriorityQueue is a home made class? or where can i find it?

Example adress:
XML Code: 
http://www.cs.cityu.edu.hk/~lwang/cs5302/Textbook/Java/source/datastructures/Dijkstra.java
It would be nice to understand what is happening ;P thanks...