you need to define object of random Class and generate random number with the help of this object just like below
Random a = new Random();
int b = a.nextInt(5 - 1) + 1;<-------------- generating random number
switch (b) {
case 1:
start.youranimationhere()
break;
case 2:
start.youranimation2here()
break;
break;
case 3:
//do your job for all case that you declare variable b above