Question

I want to use an interface like this :

public interface ResultItem {
    public int getConfidence();
    public boolean equals(ResultItem item);
    public ResultItem cloneWithConfidence(int newConfidence);
}

I have it implemented by different kind of objects representing a voice recognition result.

The idea is, I wish to compare only results of the same kind. That is, if I create a class IntResult implementing ResultItem, I want that the method signatures become :

public boolean equals(IntResult item);
public IntResult cloneWithConfidence(int newConfidence);

I feel that there is a design flaw in my interface, because for now I am using pretty ugly casts on the results of cloneWithConfidence and of other methods returning a ResultItem.

Is there a better way?

Answer 1

There is a frequently-seen idiom that goes as follows:

public interface ResultItem<T extends ResultItem<T>> {
    public int getConfidence();
    public boolean equals(T item);
    public T cloneWithConfidence(int newConfidence);
}

public class IntResult implements ResultItem<IntResult> {
  //...
}