如何在java中将月份转换为确切的天数

I have a requirement where I have to compare 2 variables. One is difference between 2 dates i.e., "Purchase Date" and "Date Call Received" which is coming as days. And the other one is Warranty length which is coming from UI as Months. Now, I am not able to compare these 2, as one is in months and other is in days. Could someone please help me how to convert months to days so that I can move forward.I have a requirement where I have to compare 2