collections - addAll() implementation -- Java -

addall() of abstractcollection implemented follows:

public boolean addall(collection<? extends e> c) {      boolean modified = false;     (e e : c) if (add(e)) modified = true;      return modified; } 

so, if c in parameter collection of, 3 elements, may case first 2 of these elements added, 3rd isn't added reason can't think of right now.

in case, addall() operation-- addition of of these 3 elements underlying collection isn't carried , addall() returning false should. however, first 2 elements there-- , developer expect shouldn't be(?)

hashset using addall() in constructor-with-a-single-param of type collection.

so, developer end hashset instance contains part of collection while he`s looking entire collection. , happens without warnings.

the methods involved-- put() of hashmap , add() of hashset seem straightforward enough-- doesn`t seem can go wrong during these operations-- still.

am missing here?

so, developer end hashset instance contains part of collection while he`s looking entire collection. , happens without warnings.

not true. fact set.add returns false means there. exceptions bounded collections have size limits, @ point developer should know it's bounded collection anyway , won't contain elements. collections in collections api, calling addall guarantees containsall return true if call same collection. i.e. print true:

set<t> set1 = new hashset<>(); set<t> set2 = new hashset<>(); // add stuff sets set1.addall(set2); system.out.println(set1.containsall(set2));