Question

I have an ArrayList of objects, which I need to sort using two attributes (using Comparators). I need to save the sorted output to a text file with a different name, depending on the attribute used to sort. For example, if the list is sorted by attribute1 then file will be attribute1.txt, if attribute2 the file will be attribute2.txt.

How I want it to work (pseudocode):

if(sortedByAtr1){
    FileWriter fwstream = new FileWriter(sortedByAtribute1.getName()+".txt");   
}
else(sortedByAtr2){
    FileWriter fwstream = new FileWriter(sortedByAtribute2.getName()+".txt");
}

Is this possible?
I appreciate any advice.
Thanks.

Servo

Answer 1

Here’s an object-oriented approach to solving this requirement.

Use a wrapper for the List and its sorting attribute:

public class ListSorter<V> {

    private final List<V> values;
    private String sortingAttribute;

    public ListSorter(List<V> values) {
        this.values = values;
    }

    public void sort(AttributeComparator<V> comparator) {
        Collections.sort(values, comparator);
        sortingAttribute = comparator.getSortingAttribute();
    }

    public String getSortingAttribute() {
        return sortingAttribute;
    }
}

Extend the Comparator interface so you can get your attribute name:

public interface AttributeComparator<T> extends Comparator<T> {
    public String getSortingAttribute();
}

Create custom AttributeComparators like this:

public class FooBarComparator implements AttributeComparator<Foo> {

    public int compare(Foo foo1, Foo foo2) {
        // skipped nullchecks for brevity
        return foo1.getBar().compare(foo2.getBar());
    }

    public String getSortingAttribute() {
        return "bar";
    }

}

Use:

List<Foo> yourList = new ArrayList<Foo>();
ListSorter<Foo> example = new ListSorter<Foo>(yourList);
AttributeComparator comparator1 = new FooBarComparator();
example.sort(comparator1);
FileWriter fwstream = new FileWriter(example.getSortingAttribute() +".txt");