String and null

[ronnir paterl]

hi,
I'm a bit confused about null. As i understand, null is a reserved keyword, represents a void reference and doesn't have a value.

Here's my question. why does this code fragment give output as "nullhi".

String abc = null;
abc+="hi";
System.out.println(abc);


Why is null considered to be a sting here?



Thank You

[marc weber]

JLS - 15.18.1 String Concatenation Operator +...

If only one operand expression is of type String, then string conversion is performed on the other operand to produce a string at run time.

JLS - 15.18.1.1 String Conversion...

If the reference is null, it is converted to the string "null" (four ASCII characters n, u, l, l).

[Henry Wong]

The key is this line of code:

 abc+="hi";

This is syntactic sugar. The compiler will create a string buffer/builder, append the null (abc reference), append the "hi" string, and assign the resultant string to the abc reference.

A string buffer/builder will convert a null reference to the "null" string, when you try to append it.

Henry