Coding Question in Hadoop

[Sush Bathin]

Hi, I have been reading a book called pro hadoop. There is a line of code I don't understand. Can someone please help me to understand the below method what it actually means.


//Sort ascending my month and descending my day of the week

public int compareTo(MonthDoWWritable second) {
        if(this.month.get()==second.month.get()){
            return -1*this.dayOfWeek.compareTo(second.dayOfWeek);
        }
        else{
            return 1*this.month.compareTo(second.month);
        }
    }

The above code is in github and Im sharing that here : https://github.com/augusto/hadoop-sandbox/blob/master/src/main/java/org/apress/prohadoop/c6/MonthDoWWritable.java

Thank you!

[Junilu Lacar]

The comment pretty much summarizes the intent. The -1* inverts the logic of the compareTo() method and essentially causes a descending sort order. The 1* part is redundant but I suspect it was just added to emphasize the ascending sort order.

[Campbell Ritchie]

Junilu Lacar wrote:. . . . The -1* inverts the logic of the compareTo() method . . .

I don't know whether it is any different from Java®, but in Java® a simple negation of the result of a comparison method is error‑prone. You will find an explanation in this Java™ Tutorials page.

[Sush Bathin]

So, if I understand correctly. The month is 1 and week is 4
.. if this.month =1 and passed month is 2 as 1==2(which is not equal) it goes to else part which is

return 1*this.month.compareTo(second.month);

so 1* (1=this.month).compareTo(?) where does second.month goes?
-----------------------------------------
case 2:
lets say the passed value is equal (1==1)

return -1*this.dayOfWeek.compareTo(second.dayOfWeek)

return -1*4.compareTo(?) I dont get that part.

[Monica Shiralkar]

I think instead of relating this to hadoop, if we understand it simply as core Java coding ,then it is easier to understand. Infact , it has nothing to do with Hadoop and all with code Java.

[Mike Simmons]

This is old now, but...

I would also add that the variable name "second" is confusing here.  It's apparently intended as the name of the other object being compared to, the second object.  But since we see the name "second" next to "month" and "day of week", it can easily sound like it refers to seconds as a measure of time.  Bad choice of name - if they'd just called the other object "other", it would have been much clearer.