How can I initialize List<List<Integer>>
in Java?
I know List
is an interface and I can use ArrayList
or LinkedList
to implement List<Integer> list = new ArrayList<Integer>()
, but when I initialize List<List<Integer>> list = new ArrayList<ArrayList<Integer>>();
I get error incompatible types:
ArrayList<ArrayList<Integer>> cannot be converted to List<List<Integer>>.
So how can I proceed?
Use
List<List<Integer>> list = new ArrayList<List<Integer>>();
or since Java 1.7
List<List<Integer>> list = new ArrayList<>();
You can define it as List<List<Integer>> list = new ArrayList<List<Integer>>();
.
Then while defining the inner List
you can take care of initialising it as ArrayList<Integer>
.
您可以将其定义为List<List<Integer>> list = new LinkedList();
You can initialize this as
List<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();
Note that the inner List has to be an implementation of the List interface, eg, ArrayList.
Since List is an interface, one can't have objects of the type List itself.
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