$ javac ConcatShapes.java && javap -c -p ConcatShapes   (method one)
  public static java.lang.String one(java.lang.String, int);
    Code:
         0: aload_0
         1: iload_1
         2: invokedynamic #7,  0              // InvokeDynamic #0:makeConcatWithConstants:(Ljava/lang/String;I)Ljava/lang/String;
         7: areturn

$ javac -XDstringConcat=inline ConcatShapes.java && javap -c -p ConcatShapes   (method one)
  public static java.lang.String one(java.lang.String, int);
    Code:
         0: new           #7                  // class java/lang/StringBuilder
         3: dup
         4: invokespecial #9                  // Method java/lang/StringBuilder."<init>":()V
         7: ldc           #10                 // String user=
         9: invokevirtual #12                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
        12: aload_0
        13: invokevirtual #12                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
        16: ldc           #16                 // String  n=
        18: invokevirtual #12                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
        21: iload_1
        22: invokevirtual #18                 // Method java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilder;
        25: invokevirtual #21                 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
        28: areturn