Difference between casting to int and intValue() method in Java

Question

I have a long value that needed to be converted to an integer. When I use casting, time to time integer value gives a minus value, which is not expected. But when I use the intValue() method in Long, the expected results comes.

I want to know the difference of casting and using intValue() method

1. Casting Example

   int days = (int) ((toDate.getTime() - fromDate.getTime()) / (1000 * 60 * 60 * 24));

2. intValue Example

   int days = ((Long) ((toDate.getTime() - fromDate.getTime()) / (1000 * 60 * 60 * 24))).intValue();

Edit: More Elaborate Example to show minus values without overflow as suggested in comments. Before casting the result is 27. When casting, the value becomes -22. But if intValue method is used, the result is 27.

Code

            System.out.println("nextDeliveryDate = " + nextDeliveryDate);
            System.out.println("nextDeliveryDate.getTime() = " + nextDeliveryDate.getTime());
            System.out.println("expectedDeliveryDate = " + expectedDeliveryDate);
            System.out.println("expectedDeliveryDate.getTime() = " + expectedDeliveryDate.getTime());
            System.out.println("nextDeliveryDate.getTime() - expectedDeliveryDate.getTime() = " + (nextDeliveryDate.getTime() - expectedDeliveryDate.getTime()));
            System.out.println("(nextDeliveryDate.getTime() - expectedDeliveryDate.getTime()) / (1000 * 60 * 60 * 24) = " + (nextDeliveryDate.getTime() - expectedDeliveryDate.getTime()) / (1000 * 60 * 60 * 24));
            System.out.println("((int) (nextDeliveryDate.getTime() - expectedDeliveryDate.getTime()) / (1000 * 60 * 60 * 24)) = " + ((int) (nextDeliveryDate.getTime() - expectedDeliveryDate.getTime()) / (1000 * 60 * 60 * 24)));
            System.out.println("((Long) ((nextDeliveryDate.getTime() - expectedDeliveryDate.getTime()) / (1000 * 60 * 60 * 24))).intValue() = " + ((Long) ((nextDeliveryDate.getTime() - expectedDeliveryDate.getTime()) / (1000 * 60 * 60 * 24))).intValue());

Results

Info: nextDeliveryDate = Thu May 14 00:00:00 IST 2015
Info: nextDeliveryDate.getTime() = 1431541800000
Info: expectedDeliveryDate = Fri Apr 17 00:00:00 IST 2015
Info: expectedDeliveryDate.getTime() = 1429209000000
Info: nextDeliveryDate.getTime() - expectedDeliveryDate.getTime() = 2332800000
Info: (nextDeliveryDate.getTime() - expectedDeliveryDate.getTime()) / (1000 * 60 * 60 * 24) = 27
Info: ((int) (nextDeliveryDate.getTime() - expectedDeliveryDate.getTime()) / (1000 * 60 * 60 * 24)) = -22
Info: ((Long) ((nextDeliveryDate.getTime() - expectedDeliveryDate.getTime()) / (1000 * 60 * 60 * 24))).intValue() = 27

Answer 1

I don't think your results should be different, because here is what the Long.intValue() method does:

public int intValue() {
    return (int)value;
}

Something isn't right with your control flow between those two lines.

You can try this test below:

Calendar now = Calendar.getInstance();
Date fromDate = now.getTime();
now.add(Calendar.YEAR, 10);
Date toDate = now.getTime();

System.out.println("line 0: " + (toDate.getTime() - fromDate.getTime()));
System.out.println("line 1: " + (int)(toDate.getTime() - fromDate.getTime()));
System.out.println("line 2: " + new Long((toDate.getTime() - fromDate.getTime())).intValue());

int days = (int) ((toDate.getTime() - fromDate.getTime()) / (1000 * 60 * 60 * 24));

System.out.println("line 3: " + days);

days = ((Long) ((toDate.getTime() - fromDate.getTime()) / (1000 * 60 * 60 * 24))).intValue();

System.out.println("line 4: " + days);