How to get minimum from list of integer in O(1) using stack.

Source Code:
Github: MinimumFinder.java

Output:

MinimumFinder {elementStack=[2, 6, 1, 5, 1, 4, 2], minimumStack=[1, 1, 2]}
Minimum : 1
Pop : 2
Pop : 6
Pop : 1
Pop : 5
MinimumFinder {elementStack=[1, 4, 2], minimumStack=[1, 2]}
Minimum : 1
Pop : 1
MinimumFinder {elementStack=[4, 2], minimumStack=[2]}
Minimum : 2