ContainsAll List Java

     List<String> a = new ArrayList<String>();
     List<Str开发者_如何学JAVAing> 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?

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Because B is empty. A contains everything in B.

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

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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.

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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.

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