Question

Below is the method I have. It works fine for comparing Strings. I would like to make it capable of also comparing Dates or possibly any class that has an acceptably defined compareTo method. Looking for an easy way to do this. I was heading down a hacky path. Also open to any other suggestions to improve this method.

protected <E> int compareFields(E o1, E o2,String fieldName){
    String o1Data;
    String o2Data;
    try { 
        o1Data = (String) o1.getClass().getMethod(fieldName).invoke(o1);
        o2Data = (String) o2.getClass().getMethod(fieldName).invoke(o2);
    }
    catch(Exception e) {
        throw new RuntimeException(e);
    }
    if(o1Data == null && o2Data == null){
        return 0;
    } else if (o1Data == null){
        return 1;
    } else if (o2Data == null){
        return -1;
    }
    return o2Data.compareTo(o1Data);
}

Answer 1

Do you mean like the following?

protected <E> int compareFields(E o1, E o2, String fieldName){
    try { 
        Comparable o1Data = (Comparable) o1.getClass().getMethod(fieldName).invoke(o1);
        Comparable o2Data = (Comparable) o2.getClass().getMethod(fieldName).invoke(o2);
        return o1Data == null ? o2Data == null ? 0 : 1 :
               o2Data == null ? -1 : o1Data.compareTo(o2Data);
    } catch(Exception e) {
        throw new RuntimeException(e);
    }
}

I assume you don’t want to reverse sort your data.