包含所有列表Java

Question

     List<String> a = new ArrayList<String>();
     List<String> b = new ArrayList<String>();

     a.add("apple");
     a.add("orange");

     System.out.println(a.containsAll(b));

The above program prints a True. Dont understand why is it printing True?

Answer 1

Because B is empty. A contains everything in B .

Answer 2

Because b is empty. Therefore there is nothing in b that is not in a .

Answer 3

It's a matter of logic: does A contain all the elements inside B?

This can be seen as for each element in B, does this element belong to A too?

You can understand that the condition is true, since B is empty, there is no element to check: for each element in B, so for no element.

Answer 4

List.ContainsAll will return true if the list contains all of the elements within the target. Because B is empty A contains all the same elements as B.

Answer 5

Obviously a typo. b.add("orange") is what was meant.