In Java, I'm trying to know whether an Integer is in an ArrayList<Integer>.
I tried using this general solution, which warns that it doesn't work with arrays of primitives. That shouldn't be a problem, since Integers aren't primitives (ints are).
ArrayList<Integer> ary = new ArrayList<Integer>();
ary.add(2);
System.out.println(String.format("%s", Arrays.asList(ary).contains(2)));
Returns false.
Any reason why?
Any help is appreciated, although the less verbose the better.
Any reason why it returns
false?
Simply because Arrays.asList(ary) will return a List<ArrayList<Integer>> and you try to find if it contains an Integer which cannot work.
As remainder here is the Javadoc of Arrays.asList(ary)
public static <T> List<T> asList(T... a)Returns a fixed-size list backed by the specified array.
Here as you provide as argument an ArrayList<Integer>, it will return a List of what you provided so a List<ArrayList<Integer>>.
You need to call List#contains(Object) on your list something like ary.contains(myInteger).
The problem is that you're trying to coerce your ArrayList to a List when it already is. Arrays.asList takes an array or variable number of arguments and adds all of these to a list. All you need to do is call System.out.println(ary.contains(2));
You don't need asList() as ArrayList itself a list. Also you don't need String.format() to print the result. Just do in this way. This returns true :
System.out.println(ary.contains(2));
Arrays.asList(ary)?arywas declared as anArrayList<Integer>?ArrayList<T>inherited fromList<T>and thus already had acontains()method... This was kind of a trivial question, so I'll leave it up to the community to decide whether to keep it or not.