Unique Java Objects in a LinkedHashSet

Question

I want to create a top 5 list of unique key value pairs sorted according to a value.

I have tried creating a Hashmap but since the original list that i read from JSON is sorted Hashmap overwrites the last value so they key will have the smallest value instead of the largest.

The solution was to use LinkedHashSet, to ensure uniqueness and keep the order. But since i am storing a key, value pairs i decided to create a new class and save them as objects.

I know that i had to implement comparable but apparently there is no comparison happening and the LinkedHashSet is not unique.

My Code is:

public class cellType implements Comparable<Object> {

private String type;
private double confidence;

@Override
public String toString() {
    return "type=" + type + " - confidence=" + confidence ;
}

public cellType(String type, double confidence) {
    super();
    this.type = type;
    this.confidence = confidence;
}
public String getType() {
    return type;
}
public void setType(String type) {
    this.type = type;
}
public double getConfidence() {
    return confidence;
}
public void setConfidence(double confidence) {
    this.confidence = confidence;
}
@Override
public boolean equals(Object obj) {
    if (!(obj instanceof cellType)) {
          return false;
        }
    cellType ct = (cellType) obj;
    return type.equals(ct.getType());
}
@Override
public int compareTo(Object o) {
    cellType ct = (cellType) o;
    return type.compareTo(ct.getType());
}

}

    public static void main(String args[]) throws IOException, JSONException {
    String freebaseAddress = "https://www.googleapis.com/freebase/v1/search?query=";
    System.setProperty("https.proxyHost", "proxy");
    System.setProperty("https.proxyPort", "8080");
    JSONObject json = readJsonFromUrl(freebaseAddress + "apple");
    LinkedHashSet<cellType> rich_types = new LinkedHashSet<cellType>();
    JSONArray array = json.getJSONArray("result");
    for (int i = 0; i < array.length(); i++) {
        if (array.getJSONObject(i).has("notable")) {
            JSONObject notable = new JSONObject(array.getJSONObject(i)
                    .getString("notable"));
            if (rich_types.size() <= 5)
                rich_types.add(new cellType(notable.getString("name"), (Double) array.getJSONObject(i).get("score")));
        }
    }
    System.out.println(rich_types);
}

The output is:

[type=Monarch - confidence=79.447838, type=Monarch - confidence=58.911613, type=Monarch - confidence=56.614368, type=Founding Figure - confidence=48.796387, type=Politician - confidence=38.921349, type=Queen consort - confidence=36.142864]

Answer 1

I think you mean you want to use TreeMap (Map not Set) to use Comparable keys to sort them. LinkedHashSet is a collection of elements which keep the order they were added.

It sounds like what you want is

if (rich_types.size() <= 5) {
    cellType ct = new cellType(notable.getString("name"), (Double) array.getJSONObject(i).get("score"));
    if(!rich_type.contains(ct))
        rich_types.add(ct);
}

Answer 2

You need to implement hashCode() too.
Anyone who even considers implementing equals() and hashCode() needs to read at least this chapter of Effective Java or better yet the whole book.