How is concatenation of final strings done in Java?

Question

When I compile this snippet.

public class InternTest {
    public static void main(String...strings ){
        final String str1=\"str\";
        final Strin         


        

Answer 1

http://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.28 says that

Simple names (§6.5.6.1) that refer to constant variables (§4.12.4) are constant expressions.

http://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.28 also says:

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)
• [...]
• The additive operators + and - (§15.18)
• [...]
• Simple names (§6.5.6.1) that refer to constant variables (§4.12.4).

Example 15.28-1. Constant Expressions

[...]

"The integer " + Long.MAX_VALUE + " is mighty big."

Since those two variables are constant expressions, the compiler does the concatenation:

String str = str1 + str2;

is compiled the same way as

String str = "str" + "ing";

which is compiled the same way as

String str = "string";