流式传输不同的数据

Question

I'm getting my head around Streams API.

What is happening with the 2 in the first line? What data type is it treated as? Why doesn't this print true ?

System.out.println(Stream.of("hi", "there",2).anyMatch(i->i=="2"));

The second part of this question is why doesn't the below code compile ( 2 is not in quotes )?

System.out.println(Stream.of("hi", "there",2).anyMatch(i->i==2));

Answer 1

In the first snippet, you are creating a Stream of Object s. The 2 element is an Integer , so comparing it to the String "2" returns false.

In the second snippet, you can't compare an arbitrary Object to the int 2, since there is no conversion from Object to 2 .

For the first snippet to return true, you have to change the last element of the Stream to a String (and also use equals instead of == in order not to rely on the String pool):

System.out.println(Stream.of("hi", "there", "2").anyMatch(i->i.equals("2")));

The second snippet can be fixed by using equals instead of == , since equals exists for any Object :

System.out.println(Stream.of("hi", "there",2).anyMatch(i->i.equals(2)));

Answer 2

You should instead make use of:

System.out.println(Stream.of("hi", "there",2).anyMatch(i->i.equals(2)));

The reason for that is the comparison within the anyMatch you're doing is for i which is an Object (from the stream) and is incompatible with an int .

Also, note that the first part compiles successfully since you are comparing an integer(object) with an object string "2" in there and hence returns false.