Why I get a compiler error (cannot cast from long to Long) on a TimeUnit to a date, while if i change the java compiler i don't get it anymore

Question

I have this code, and on the last line compiler gives me error: Cannot cast from long to Long. If i change my java compiler, i uncheck the checkbox "Use compliance from execution enviroment CDC-1.1/Foundation.1-1 on the java BUild path" and i select a compliance compiler level 1.7 I don't get the error anymore? And there is a way to don't get that error don't changing java compiler compliance?

package data;

import java.util.Date;
import java.util.Calendar;
import java.util.concurrent.TimeUnit;

public class DataProva {

    public static void main(String[] args) {


        Calendar cal1 = Calendar.getInstance(); 
        Calendar cal2 = Calendar.getInstance();  

        cal2.set(2010,0,1,12,0);

        Date date1 = cal2.getTime();

        System.out.println(date1);  

        long mill = Math.abs(cal1.getTimeInMillis() - date1.getTime());


        long hours = TimeUnit.MILLISECONDS.toHours(mill);


        Long dayss = TimeUnit.HOURS.toDays(hours); // here i get compiler error cannot cast from long to Long

Thank you so much!

EDIT: I changed long dayss to Long because java changed it. I have still 2 question: 1) Why my java use such old version to compile. 2) Why the if i cast it like this: Long dayss = (Long) TimeUnit.HOURS.toDays(hours); doesn't work the same. How can i build a wrapper then in java 1.4

Each project i do start like this:

Answer 1

Java 1.5 adds a feature called auto-boxing, which implicitly converts between primitive types (like long ) and boxed wrapper types (like Long ).

Earlier versions do not have this feature, so you need to construct the wrapper types yourself.

Answer 2

if you want to continue to use Java 1.4 then replace this

Long dayss = TimeUnit.HOURS.toDays(hours); // here i get compiler error cannot cast from long to Long

to this

Long dayss = Long.valueOf(TimeUnit.HOURS.toDays(hours)); // here i get compiler error cannot cast from long to Long

Actually that is better coding practice no matter which version of java your using.