Question

I’m converting an application to use Java 1.5 and have found the following method:

  /**    * Compare two Comparables, treat nulls as -infinity.    * @param o1    * @param o2    * @return -1 if o1<o2, 0 if o1==o2, 1 if o1>o2    */   protected static int nullCompare(Comparable o1, Comparable o2) {     if (o1 == null) {       if (o2 == null) {         return 0;       } else {         return -1;       }     } else if (o2 == null) {       return 1;     } else {       return o1.compareTo(o2);     }   } 

Ideally I would like to make the method take two Comparables of the same type, is it possible to convert this and how?

I thought the following would do the trick:

protected static <T extends Comparable> int nullCompare(T o1, T o2) { 

but it has failed to get rid of a warning in IntelliJ ‘Unchecked call to ‘compareTo(T)’ as a member of raw type ‘java.lang.Comparable” on the line:

return o1.compareTo(o2); 

Answer 1

Change it to:

protected static <T extends Comparable<T>> int nullCompare(T o1, T o2) { 

You need that because Comparable is itself a generic type.