Kruskal's algorithm in Java

Kruskal's algorithm is well known for finding MST or minimum spanning tree. First it sorts all the edges in non-decreasing order. Then, it keeps taking edges from the sorted list given that, at least one of the vertices at two ends of the edge is not discovered before. Current implementation uses java and pretty straight forward approach. It can be further improved by imporving sorting algorithm and using a custom Set data structure for set operations.