CODEWITHSUNDEEP
java
olaf
olaf

Reputation: 347

Are string literal concatenation using + in log parameter store in compiler constant pool?

Consider the following

log.info("very long string  {}, " + " another string {}", a, b)

vs

log.info("very long string {}, another string {}", a, b)

In java specification https://docs.oracle.com/javase/specs/jls/se7/html/jls-3.html#jls-3.10.5

String literals are stored in compiler constant and create in compile time

String x = "very long string " + "another string"

is equal to

String y = "very long string another string"

Both x and y share the same reference because they are literals that are evaluated at compile time.

But is that true if the string are part of perameter calls?

Upvotes: 0

Views: 40

Answers (1)

rgettman
rgettman

Reputation: 178303

Yes, you have a constant expression, according to the JLS, Section 15.29.

Constant expressions of type String are always "interned" so as to share unique instances, using the method String.intern.

Your expression is made of string literals and the + operator, which are in the list of things allowed in constant expressions.

A constant expression is an expression denoting a value of primitive type or a String that does not complete abruptly and is composed using only the following:

  • Literals of primitive type (§3.10.1, §3.10.2, §3.10.3, §3.10.4), string literals (§3.10.5), and text blocks (§3.10.6)

(snip)

  • The additive operators + and - (§15.18)

There is no mention of any limitations based on context as to whether it's a constant expression, so even it's being passed to a method, it's still a constant expression, and it's still stored in the interned string pool.

Upvotes: 1

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