Days between two dates

Given two dates in AD, find number of days between these 2 dates
https://github.com/mission-peace/interview/blob/master/src/com/interview/misc/DayDifferenceBetweenTwoDates.java
    private static final int days[] = {31,28,31,30,31,30,31,31,30,31,30,31};
 
    public int diff(int year1,int month1, int day1,int year2, int month2,int day2){
        int days1 = year1*365 + day1;
        int days2 = year2*365 + day2;
     
        for(int i=0; i < month1-1; i++){
            days1 = days1 + days[i];
        }
 
        for(int i=0; i < month2-1; i++){
            days2 = days2 + days[i];
        }
     
        days1 = days1 + (year1-1)/4  - (year1 -1)/100 + (year1 -1 )/400;
        days2 = days2 + (year2-1)/4  - (year2 -1)/100 + (year2 -1 )/400;
     
        if(isLeapYear(year1) && month1 > 2){
            days1++;
        }
        if(isLeapYear(year2) && month2 > 2){
            days2++;
        }
     
        return days2 - days1;
    }
 
 
    public boolean isLeapYear(int year){
        if(year % 400 == 0){
            return true;
        }
        if(year % 4 == 0 && year % 100 != 0){
            return true;
        }
        return false;
    }
https://github.com/mission-peace/interview/blob/master/src/com/interview/misc/DifferenceBetweenTwoTime.java
* Given two times in four digits number e.g 10:10 is 1010 find difference between them
* Test cases
* Time 1 better be less than equal to time 2
* First 2 digits better be between 0 and 23
* Last 2 digits of number better be between 0 to 59
   public int diff(int time1, int time2){
       if(time2 < time1){
           throw new IllegalArgumentException();
       }
     
       int hourDiff = time2/100 - time1/100 -1;
       int minDiff = time2%100 + (60 - time1%100);
       if(minDiff >= 60){
           hourDiff++;
           minDiff = minDiff - 60;
       }
       return hourDiff*100 + minDiff;
   }