[JAVA] I was addicted to the roll method

The roll method of the Calendar class specifies which part of the date to change in the first argument and the change value in the second argument.

If there is a variable with 4/1 set, what happens to the value of the variable when it is executed with "day" as the first argument and "-1" as the second argument of the roll method?

It is likely to be 3/31 because the day goes back one day, but it will actually be 4/30.

With the add method, it seems to be 3/31.

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