How to merge two ArrayLists without duplicates? [duplicate]

Answer 1

you can do something like this:

ArrayList<Object> result = new ArrayList<>();
result.addAll(one);

for(Object e: two){
    if(!result.contains(e))
        result.add(e);
}

Answer 2

for (Object x : two){
   if (!one.contains(x))
      one.add(x);
}

assuming you don't want to use the set suggested in the comment. If you are looking for something fancier than this please clarify your question.

Answer 3

Try this kind of thing. As Set doesn't allow duplicates you can add only the changes

ArrayList<String> a=new ArrayList<>();
a.add("a");
a.add("b");
ArrayList<String> b=new ArrayList<>();
a.add("a");
a.add("c");
Set<String> s=new HashSet<String>();
s.addAll(a);
s.addAll(b);
a=new ArrayList<>(s);
for(String r:a){
    System.out.println(r);
}

Answer 4

Either:

Set<Foo> fooSet = new LinkedHashSet<>(one);
fooSet.addAll(two);
List<Foo> finalFoo = new ArrayList<>(fooSet);

or

List<Foo> twoCopy = new ArrayList<>(two);
twoCopy.removeAll(one);
one.addAll(twoCopy);