CODEWITHSUNDEEP
javasortingcomparablecompareto
corkiiunranked
corkiiunranked

Reputation: 67

java - compareTo method

i have a question about compareTo method in java. So this compareTo method compares CarOwner objects and if the calling object is earlier in chronological time in comparison to the argument returns -1, if the calling object is later in chronological time in comparison to the argument returns 1, if the calling object and argument are the same in chronological time returns 0. if the argument passed in is not a CarOwner object (use instanceof or getClass to determine this) or is null, returns -1.

and i came up with this code, but it doesnt seem like its working, anybody have any suggestion?

public int compareTo(Object o)
{
    if ((o != null ) && (o instanceof CarOwner))
    {
        CarOwner otherOwner = (CarOwner) o;
        if (otherOwner.compareTo(getYear()) > 0)
            return -1;
        else if (otherOwner.compareTo(getYear()) < 0)
            return 1;
        else if (otherOwner.equals(getYear()))
            if (otherOwner.compareTo(getMonth()) > 0)
                return -1;
            else if (otherOwner.compareTo(getMonth()) < 0)
                return 1;
            else if (otherOwner.equals(getMonth()))
                return 0;
    }
    return -1;
}

Upvotes: 0

Views: 1704

Answers (5)

Dmitry
Dmitry

Reputation: 2149

Should work, if getYear() and getMonth() returns the comparable objects

public int compareTo(Object o)
{
    if ((o != null ) && (o instanceof CarOwner))
    {
        CarOwner otherOwner = (CarOwner) o;
        int result = otherOwner.getYear().compareTo(getYear());
        if (result != 0)
            return result;
        return otherOwner.getMonth().compareTo(getMonth());
    }
    return -1;
}

if getYear() and getMonth() returns int, then:

public int compareTo(Object o)
{
    if ((o != null ) && (o instanceof CarOwner))
    {
        CarOwner otherOwner = (CarOwner) o;
        if (otherOwner.getYear() > getYear())
            return -1
         else if (otherOwner.getYear() < getYear())
             return 1
         else if  (otherOwner.getMonth() > getMonth())
             return -1
         else if  (otherOwner.getMonth() < getMonth())
             return 1;
         else 
             return 0;
    }
    return -1;
}

Upvotes: 0

void
void

Reputation: 7890

Implement the Compareable interface on your class (Comparable<CarOwner>) after that use CarOwner for your compareTo method instead of Object (int compareTo(CarOwner otherOwner))

Upvotes: 0

Eran
Eran

Reputation: 394106

You are comparing properties of this instance to the entire otherOwner instance. You should compare to properies of otherOwner.

For example

otherOwner.getYear().compareTo(getYear())

Upvotes: 1

Patrick Chan
Patrick Chan

Reputation: 1029

As you are comparing different fields and digging deeper if year field is the same, I suggest the following

int oy=otherOwner.getYear();
int ty=this.getYear();
int om=otherOwner.getMonth();
int tm=this.getMonth();

if(oy==ty){
    return om-tm;
}else{
    return oy-ty;
}

Upvotes: 0

Pan Long
Pan Long

Reputation: 1032

If you apply the method to some CarOwner, what will happen is:

  1. Yes, it is an instance of CarOwner. We go into your if block.
  2. but when you call otherOwner.compareTo, you are passing "Year" or "Month", which I assume it is an integer or string.
  3. You then goes to compareTo method of otherOwner, your "Year" or "Month" is not an instance of CarOwner, then it always returns -1.

So what you should do is compare "Year" or "Month" with otherOwner's "Year" or "Month" and return the result.

Upvotes: 0

Related Questions