Java Venkat

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ArrayList Vs LinkedList In Java.

Sorting Array of String or objects

Solution with Collections.sort

If you are forced to use that List, or if your program has a structure like

Create List
Add some country names
sort them once
never change that list again

then Thilos answer will be the best way to do it. If you combine it with the advice from Tom Hawtin - tackline, you get:

java.util.Collections.sort(listOfCountryNames, Collator.getInstance());

Solution with a TreeSet

If you are free to decide, and if your application might get more complex, then you might change your code to use a TreeSet instead. This kind of collection sorts your entries just when they are inserted. No need to call sort().


Collection<String> countryNames = 

    new TreeSet<String>(Collator.getInstance());

countryNames.add("UK");

countryNames.add("Germany");

countryNames.add("Australia");

// Tada... sorted.

Side note on why I prefer the TreeSet

This has some subtle, but important advantages:

It's simply shorter. Only one line shorter, though.
Never worry about is this list really sorted right now becaude a TreeSet is always sorted, no matter what you do.
You cannot have duplicate entries. Depending on your situation this may be a pro or a con. If you need duplicates, stick to your List.
An experienced programmer looks at TreeSet countyNames and instantly knows: this is a sorted collection of Strings without duplicates, and I can be sure that this is true at every moment. So much information in a short declaration.
Real performance win in some cases. If you use a List, and insert values very often, and the list may be read between those insertions, then you have to sort the list after every insertion. The set does the same, but does it much faster.

accepted

Use the function taking as second parameter a Comparator.

Il allows you to pass an instance of Comparator to sort according to your needs. Note that thejavadoc of Comparator contains guidelines regarding the building of comparators.

You may define the comparator as an anonymous class if it's only locally used. Here's an example where I sort objects regarding to one of their fields which is a String :

Collections.sort(groupResults, new Comparator<ProductSearchResult>() {
    public int compare(ProductSearchResult result1, ProductSearchResult result2) {
        return result1.product.getRsId().compareTo(result2.product.getRsId());
    }
});

Alternatively, you might also make your class implement the Comparable interface but this makes sense only if you can define a natural (obvious) order.

I would create an inner class implementing the Comparator interface:

public class Car {
public double horsePower;

class CarHorsePowerComparator implements Comparator<Car> {
    @Override
    public int compare(Car car1, Car car2) {
        return Integer.valueOf(car.horsePower).compareTo(Integer.valueOf(car2.horsePower))          }
    }
}

Now when you want to sort your Car list by horsePower:

List<Car> list = new ArrayList<Car>(myCars); //your Car list
Collections.sort(list, new CarHorsePowerComparator());

Java Venkat

Thursday, January 14, 2010

Spring with XFire Quartz

Java Technology

Sorting Array of String or objects

Solution with Collections.sort

Solution with a TreeSet

Side note on why I prefer the TreeSet