从 ArrayList 中删除重复项<jsonjavaobject>或者如何找出 arraylist 中是否已经存在类似的项目？</jsonjavaobject>

Question

I have a ArrayList collection of JsonJavaObject (derived from com.ibm.commons.util.io.json.*). When adding more items I would like to check if a similar JSsonObject already exists in the arraylist. How must I do this?

Alternatively I can think of just filling the arraylist with more JsonJavaObject and before returning the result merge the duplicates.

However when I try this eg via

TreeSet<JsonJavaObject> uniqueHits = new TreeSet<JsonJavaObject>(JSONObjects);
ArrayList<JsonJavaObject> finalHits = new ArrayList<>(uniqueHits);

I get an exception: java.lang.ClassCastException: com.ibm.commons.util.io.json.JsonJavaObject incompatible with java.lang.Comparable

at

TreeSet uniqueHits = new TreeSet(JSONObjects);

Who can help me?

Answer 1

TreeSet needs the class to implement Comparable since it wants to sort the elements according to some defined order.
Since this is unnecessary for duplicate elimination you can simply use a HashSet ie

Set<JsonJavaObject> uniqueHits = new HashSet<>(JSONObjects);
List<JsonJavaObject> finalHits = new ArrayList<>(uniqueHits);