问不能覆盖compareTo

EN

public interface Frequency {
    public int increment();
    public int decrement();
    public int freq();
    public Object getTop();
}

public class Child extends IndexedWord implements Frequency{
int freq;
TreeSet<Relation> relations;
public Child() {
    freq=0;
    relations = new TreeSet<Relation>(new FreqCompare<Relation>());
}

public void addRelation(Relation relation) {
    relations.add(relation);
}

public Relation getTop() {
    Relation top=relations.first();
    top.decrement();
    return top;
}

@Override
public int increment() {
    freq++;
    return freq;
}
@Override
public int decrement() {
    freq--;
    return freq;
}

@Override
public int freq() {
    return freq;
}

@Override
public int compareTo(Object obj) {
    return 0;
}
}