Java 8 Stream distinct is not working -


this doing: 

list scores = stream.concat(oldentries.stream(), newentries.stream())                     .sorted()                     .distinct()                     .limit(maxsize)                     .collect(collectors.tolist());

i expecting sorted list without duplicates, times there duplicate in list.

i have override hashcode , equals method, have observed these methods returning correct value every time. can 1 see wrong stream?

this equals() , hashcode() auto generated idea :

.. private int userid; private int levelid; private int score;  @override public boolean equals(object o) {      if (this == o) return true;     if (o == null || getclass() != o.getclass()) return false;      score score = (score) o;      if (userid != score.userid) return false;     return levelid == score.levelid;  }  @override public int hashcode() {     int result = userid;     result = 31 * result + levelid;     return result; }  public int compareto(score other) {      if (other == null) {         return 1;     } else {         return integer.compare(other.score, this.score);     } }   ..

your stream first ordered according compareto, i.e. using score.

it's "distinctified" using equals(), i.e. using userid , levelid. according javadoc:

for ordered streams, selection of distinct elements stable (for duplicated elements, element appearing first in encounter order preserved.) unordered streams, no stability guarantees made.

example:

score 1, user 2, level 3 score 3, user 2, level 3 score 1, user 3, level 1

after sorting...

score 1, user 2, level 3 score 1, user 3, level 1 score 3, user 2, level 3

distinct nothing, because elements not equal according user/level. can result in "duplicate" elements, because you're ordering stream based on 1 thing, determining equality entirely different thing.


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