collections addAll method !!!!

[amit patidar]

Hi All,

public static void main(String[] args) {

List<Integer> listA = new ArrayList<Integer>();
List<Integer> listB = new ArrayList<Integer>();

listA.add(1);
listA.add(2);
listA.add(3);
listA.add(4);

listB.add(1);
listB.add(2);


listA.addAll(listB);

for(Integer ele : listA){
System.out.print(ele);
}

}


Program prints values from both the list (listA and listB) (1,2,3,4,1,2).

or the result should be union of listA and listB ie listA Union listB ie (1,2,3,4)

Please Help.

[Rob Spoor]

If you want unique values only use a Set: HashSet, LinkedHashSet or TreeSet.

[Ankit Garg]

Looking at your requirement, you can do this

listA.removeAll(listB); //this will remove all the elements in listA which are also in listB
listA.addAll(listB); 

Also please Use Code Tags when posting a source code...

[amit patidar]

so this is not the implementation of addAll() method which helps in union of the result , these are the property of Set implementation classes which maintains unique elements

so this is clear that only Set: HashSet, LinkedHashSet or TreeSet have this case , all other collections implementing addAll() will give complete result ie listone +listtwo+..................listn

[Rob Spoor]

It determines on the Collection type whether or not it will contain duplicates.

For List, yes, you will get all elements from all lists, with duplicates. In the end, result.size() == list1.size() + list2.size() + ... + listn.size().
Set will only contain one copy of each value, so it will really be the union.
Queue and Deque behave a bit like List I believe.
Other collection types, who knows. Check the API of the type to see what it tells you.

[amit patidar]

i will have a look on other collection types

but now the view is clear

Thank you Rob