Not implementing all the methods of an interface

Question

I tried reproducing the code below on eclipse. I get an error telling me that I have to implement all the inherited methods (because Comparator is an interface).

The type new Comparator(){} must implement the inherited abstract method Comparator.reversed().

There are many of these methods and the only one I want to overwrite is compare. Do I have to implement all the other methods or is there a way to specify I don't need to implement them? I understand that I will have to do it because of the contractual nature of an interface, but what if I just need to change one method?

static Map sortByValue(Map map) {
     List list = new LinkedList(map.entrySet());
     Collections.sort(list, new Comparator() {
          public int compare(Object o1, Object o2) {
               return ((Comparable) ((Map.Entry) (o1)).getValue())
              .compareTo(((Map.Entry) (o2)).getValue());
          }
     });

    Map result = new LinkedHashMap();
    for (Iterator it = list.iterator(); it.hasNext();) {
        Map.Entry entry = (Map.Entry)it.next();
        result.put(entry.getKey(), entry.getValue());
    }
    return result;
} 

EDIT Solved by changing the compliance level to java8 in eclipse luna. Thanks!

Answer 1

The type new Comparator(){} must implement the inherited abstract method Comparator.reversed() then if I apply the fix, I have many functions added

Comparator.reversed was introduced in Java 1.8 and it's a default method i.e. a method that you don't have to override.

It seems like you have your compliance level set to pre Java 1.8 (since Eclipse asks you to override reversed), while using Java 1.8 API (since Comparator has a reversed method).

Make sure you either change your API to 1.7 or change your compliance level to 1.8. (The latter option requires Eclipse Luna or better.)

More on Eclipse compliance level: What is "compiler compliance level" in Eclipse?