How many Strings are created in memory?

Question

Say I have this String expression

String hi = "Tom" + "Brady" + "Goat"

I know that the String pool "allows a runtime to save memory by preserving immutable strings in a pool" String Pool

How many strings will be created in the string pool?

My initial guess was 5 - "Tom", "Brady", "Goat", "TomBrady","TomBradyGoat", because of the order of operations of String concatenation (left to right?) or is it only the final result, "TomBradyGoat", that is stored in the String pool?

Answer 1

What you have here is a constant expression, as defined by the JLS, Section 15.28.

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 and literals of type String (§3.10.1, §3.10.2, §3.10.3, §3.10.4, §3.10.5)

• Casts to primitive types and casts to type String (§15.16)

• The unary operators +, -, ~, and ! (but not ++ or --) (§15.15.3, §15.15.4, §15.15.5, §15.15.6)

• The multiplicative operators *, /, and % (§15.17)

• The additive operators + and - (§15.18)

(other possibilities)

The compiler determines that the expression "Tom" + "Brady" + "Goat" is a constant expression, so it will evaluate the expression itself to "TomBradyGoat".

The JVM will have only one string in the string pool, "TomBradyGoat".

Answer 2

At runtime, that piece of code will translate into a single String object. The compiler will take care of concatenation at compile time and add a single value in the constants pool.