java comparator on multidimensional array

Question

Is there a better way to write this comparator? I have an equivalent of multidimensional array where columns are Object's. The actual objects are String and BigDecimal 99% of the time. I am sorting "rows" on a given column index.

I want to avoid instanceof.

protected static class MyComparator implements Comparator<DataRow> {
    private int idx;

    public MyComparator(int idx) {
        this.idx = idx;
    }

    @Override
    public int compare(DataRow r1, DataRow r2) {
        Object o1 = r1.getColumns()[idx];   
        Object o2 = r2.getColumns()[idx];
        if (o1 instanceof String){
            return ((String)o1).compareTo((String)o2);
        }else if (o1 instanceof BigDecimal){
            return ((BigDecimal)o1).compareTo((BigDecimal)o2);
        }else{
            throw new UnsupportedOperationException("comparison cannot be performed");
        }
    }

Bhesh Gurung · Accepted Answer · 2011-12-16 19:22:09Z

2

Since both String and BigDecimal are Comparables:

return ((Comparable)o1).compareTo(o2);

answered Dec 16, 2011 at 19:22

Bhesh Gurung

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stacker · Accepted Answer · 2011-12-16 19:21:40Z

1

I think since you only depend on the type Comparable you could rewrite it as:

public int compare(DataRow r1, DataRow r2) {
        Comparable o1 = (Comparable) r1.getColumns()[idx];   
        Comparable o2 = (Comparable) r2.getColumns()[idx];
        return o1.compareTo(o2);
}

If you carefully populate the table you shouldn't face the UnsupportedOperationException situation.

answered Dec 16, 2011 at 19:21

stacker

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1 Comment

Elijah Over a year ago

I will have to run my app thru many tests to see if data is compatible. So far unit tests are holding steady using this approach :)) I threw in an Integer and that worked as well.

Egor · Accepted Answer · 2011-12-16 19:29:16Z

0

If the colum types are not comparable, I would implement separate comparators and make the Column class a factory for the correct comparator that should be used.

edited Dec 16, 2011 at 19:29

answered Dec 16, 2011 at 19:23

Egor

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