How to reduce one month from current date and stored in date variable using java?

Use Calendar:

Calendar cal = Calendar.getInstance();
cal.add(Calendar.MONTH, -1);
Date result = cal.getTime();

Starting from Java 8, the suggested way is to use the Date-Time API rather than Calendar.

If you want a Date object to be returned:

Date date = Date.from(ZonedDateTime.now().minusMonths(1).toInstant());

If you don't need exactly a Date object, you can use the classes directly, provided by the package, even to get dates in other time-zones:

ZonedDateTime dateInUTC = ZonedDateTime.now(ZoneId.of("Pacific/Auckland")).minusMonths(1);

Calendar calNow = Calendar.getInstance()

// adding -1 month
calNow.add(Calendar.MONTH, -1);

// fetching updated time
Date dateBeforeAMonth = calNow.getTime();