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9.11. Adding Values to a List¶
You can add values to a list. If you use
add(obj) it will add the passed object to the end of the list. Run the code below to see how the list changes as each object is added.
Notice that we added the same string to the list more than once. Lists can hold duplicate objects.
There are actually two different
add methods in the
List interface. The
add(obj) method adds the passed object to the end of the list.
add(index,obj) method adds the passed object at the passed index, but first moves over any existing values to higher indicies to make room for the new object.
Lists can only hold objects, not primitive values. This means that
int values must be wrapped into
Integer objects to be stored in a list. You can do this using
new Integer(value) as shown above. You can also just put an
int value in a list and it will be changed into an
Integer object automatically. This is called autoboxing. When you pull an
int value out of a list of
Integers that is called unboxing.
The code below has the same result as the code above. The compiler will automatically wrap the
int values in
Check your understanding
You can step through the code above by clicking on the following Example-8-5-1.
You can step through the code above by clicking on the following Example-8-5-2.
You can step through the code above by clicking on the following Example-8-5-3.