When you need to add elements to a set, you can either add a
single element or a group of elements.
1) Adding Single elements
To add a single element, you can call the add() method:
public boolean add (Object element)
The add() method takes a single argument of the element to
add. If the element is not in the set, it is added and true is returned. If the
element happens to be in the set already, because element.equals(oldElement)
returns true, then the new element replaces the old element in the collection
and false is returned. If the old element has no other references, it becomes
eligible for garbage collection.
If the set is read only, then adding an element will throw
UnsupportedOperationException.
Note:- If you need
to modify an element in a set, you should remove it, modify it and then re-add
it. If you don’t, you can consider the object lost as there is no way of
finding the object without manually traversing through all the elements. The is
true because change affects the results of hashcode().
2) Adding Another Collection
You can add a group of elements from another collection to
the set with the addAll() method:
public boolean addAll (Collection c)
element in the collection passed in will be added to current
set via the subsequent call to add() method on each element. If the underlying
set changes, true is returned. If no elements are added, false is returned. As
with add(), if equal elements are in both sets, true is returned with the new
elements replacing the old elements in the set.
If set is read-only , then it will throw
UnsupportedOperationException.
Happy LearningJ
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