Java String Concatenation Performance

decompiled.java

// decompiled with straight javap -c
//Compiled from "TestStrings.java" in JAVA 1.6.... same in newer versions.
public class TestStrings extends java.lang.Object{
public TestStrings();
  Code:
   0:	aload_0
   1:	invokespecial	#1; //Method java/lang/Object."<init>":()V
   4:	return

public static void main(java.lang.String[]);
  Code:
   // Note that "Foo " + "bar"  was replaced (by compiler) with a static string of "Foo bar"
   0:	ldc	#2; //String Foo bar
   2:	astore_1
   // Note that "OMG" + "WTF" + "BBQ" was replaced (by compiler) with a static string of "OMGWTFBBQ"
   3:	ldc	#3; //String OMGWTFBBQ
   5:	astore_2
   // String variable 'foo' + String variable 'omg' is compiler substituted with a StringBuilder construction...
   6:	new	#4; //class java/lang/StringBuilder
   9:	dup
   10:	invokespecial	#5; //Method java/lang/StringBuilder."<init>":()V
   13:	aload_1
   14:	invokevirtual	#6; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
   17:	aload_2
   18:	invokevirtual	#6; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
   21:	invokevirtual	#7; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;
   24:	astore_3
   25:	return

}

TestStrings.java

public class TestStrings {
    public static void main(String[] args) {
        String foo = "Foo " + "bar";
        String omg = "OMG" + "WTF" + "BBQ";
        String test = foo + omg;
    }
}