String.valueOf(null) & String.valueOf(s)

Question

This is not working (Throwing Nullpointer Exception)

String s =  null; 
System.out.println(s); 
System.out.println(String.valueOf(null));

But this is

String s =  null; 
System.out.println(s); 
System.out.println(String.valueOf(s));

why ?? unable to getting. I want understand logic behind.

s is variable its type is String, null is a constant it does not have a type. — SPlatten, Jan 18 '19 at 10:54

score 5 · Answer 1 · answered Jan 18 '19 at 10:53

String.valueOf(null) calls valueOf(char data[]) which in turn calls new String(data) which accesses value.length -> NPE.

String.valueOf(someString) calls valueOf(Object obj) which does return (obj == null) ? "null" : obj.toString();

General note: please use a proper IDE. This was not my "knowledge" writing this question but just me using my IDE for ~1 minute to see which methods will actually be called, I did not even run the code.

String.valueOf(null) & String.valueOf(s)

1 Answers1