stringConcatenationBytecode

   0:	ldc	#2; //String select u from
   2:	astore_1
   3:	new	#3; //class java/lang/StringBuilder
   6:	dup
   7:	invokespecial	#4; //Method java/lang/StringBuilder."<init>":()V
   10:	aload_1
   11:	invokevirtual	#5; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
   14:	ldc	#6; //String  User as u
   16:	invokevirtual	#5; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
   19:	invokevirtual	#7; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;
   22:	astore_1
   23:	getstatic	#8; //Field java/lang/System.out:Ljava/io/PrintStream;
   26:	aload_1
   27:	invokevirtual	#9; //Method java/io/PrintStream.println:(Ljava/lang/String;)V

Boa tarde, Paulo. Me interessei muito por essa visão do byteCode.
Ela é feita com o javap -c? Eu tentei com esse comando, mas não tive um retorno parecido.

eu vi a "explicação" aqui https://blog.caelum.com.br/revisitando-a-concatenacao-de-strings-stringbuilder-e-stringbuffer/