question on the working of instanceof

Question

Long l1 = null;
Long l2 = Long.getLong("23");
Long l3 = Long.valueOf(23);

System.out.println(l1 instanceof Long);  // returns false
System.out.println(l2 instanceof Long);  // returns false
System.out.println(l3 instanceof Long);  // returns true

I could not understand the output returned. I was expecting true atleast for 2nd and 3rd syso's. Can someone explain how instanceof works?

Answer 1

This has nothing to do with instanceof. The method Long.getLong() does not parse the string, it returns the contents of a system property with that name, interpreted as long. Since there is no system property with the name 23, it returns null. You want Long.parseLong()

Answer 2

l1 instanceof Long

since l1 is null, instanceof yields false (as specified by the Java languange specs)

l2 instanceof Long

this yields false since you are using the wrong method getLong:

Determines the long value of the system property with the specified name.