Sorting an Arrylist<MyType>

[Martin Vietor]

Me again, hi y'all,

I now have the problem that I would like to sort a list. It is an Arraylist<PatientInfo> with the class PatientInfo looking like this:

public class PatientInfo {
	String name;
	String firstName;
	String patNumber;
	String versNumber;;
	String birthdate;
	String doctor;
}

I would like to sort the list by name. Is that possible? Collection.sort doesn"t work, because PateitnInfo is not per se sortable. I could write a method that sorts by name, I just want to know if there is an easier way, thanks.

M

[Greg Charles]

Yes, you can, you just need to tell Java how MyType should be ordered. That's done by implementing the Comparable interface.

[Christophe Verré]

Greg Charles wrote:Yes, you can, you just need to tell Java how MyType should be ordered. That's done by implementing the Comparable interface.

Or by making a custom Comparator<PatientInfo>.

[Martin Vietor]

Riiiight. That. Um. How?

public class PatientInfo() implements Comparable {
...
}

Ok. And a comparTo method. But I just don't get at all how to. Pointers will be fine, my (brief() internet search didn't really help.
M

[Christophe Verré]

The compareTo API says :
Compares this object with the specified object for order. Returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.

You want to sort by the name of the patient. The name is a String. String is Comparable, so you can use its compareTo method to compare the name of two patients. Try to figure out how.

[Rob Spoor]

Martin Vietor wrote:public class PatientInfo() implements Comparable

That should be

public class PatientInfo implements Comparable<PatientInfo>

You want its instances to be comparable to other instances, and that's what the generic part does. It then requires you to have the following method:

public int compareTo(PatientInfo info)
{
    ...
}

Without the generics the parameter type would be Object and you would need to cast it to PatientInfo.

As for the implementation, Christophe has already told you how to do it. Simply delegate the comparison to name comparison. Just one thing to think about: do you want to search case insensitively or not? If so, String has a second comparison method for this.

[Martin Vietor]

Well thanks, here we go. I'll try to figure it out. I'm sort of a self taught "programmer", so some terms are very abstract to me. But it's always better to read up on that oneself than getting the code done by someone else, I think.

[Rob Spoor]