Unable to get random number to be generated every time object is created

I am creating an object with the same parameters multiple times over and over again. The object has a random method (using Math.random()) in it which I know should return a different number every time, but each time within the program I create a new object of that class and call the method on it, it returns the same value. How should I fix this?

place where I call the method contract:

for (int i = 0; i < 212000; i++){
            Contractions c = new Contractions(a, b);
            temp = c.contract();
            if (temp < min){
                min = temp;
            }
            if (i%1000 == 0){
                System.out.println(min);
            }
        }

method:

while (vertices.size() > 2){
        Edge randEdge = edges.get((int) (Math.random()*edges.size())); .....


return edges.size();