Possible Duplicate: Concatenating null strings in Java Please find below the code snippet String

Question

Editorial Team

Asked: June 13, 20262026-06-13T20:00:47+00:00 2026-06-13T20:00:47+00:00

Possible Duplicate:
Concatenating null strings in Java

Please find below the code snippet

String str = null;
str = str + "hi";

System.out.println(str)

The output of the above code is nullhi.

I thought the output will be hi, so kind of surprised with the output and not able to find the reason behind it.

Can someone please explain it.

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Editorial Team · Answer 1 · 2026-06-13T20:00:48+00:00

From JLS.

§15.18.1. String Concatenation Operator + (reference)

If only one operand expression is of type String, then string conversion (§5.1.11) is performed on the other operand to produce a string at run-time.

§5.1.11. String Conversion (reference)

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

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