java.util.calendar set month to 1 happens error on 2022-06-30

ADDITIONAL SYSTEM INFORMATION :
Os: Windows10 ; Java Runtime Information: java version "1.8.0_91"

A DESCRIPTION OF THE PROBLEM :
function code:
public static String acquireMonth(Integer month) throws Exception{
        SimpleDateFormat monthSdf = new SimpleDateFormat("yyyy-MM");
        SimpleDateFormat dateSdf = new SimpleDateFormat("yyyy-MM-dd");
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.MONTH,month);
        log.error(dateSdf.format(calendar.getTime()));
        return monthSdf.format(calendar.getTime());
    }

test code:
public static void main(String[] args) {
        try{
           String month = acquireMonth(1);
           System.out.println(month);
        }catch (Exception e){
            e.printStackTrace();
        }
    }

I want acquire February DateTime，I user
Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.MONTH,1);

but compiler execution result is : 2022-03
I observe JDK execution result : calendar.getTime() => 2022-03-02
I want to know why.