src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/Target.java

rev 3444 : Only use IndyStringConcat for JDK >= 9

*** 133,138 ****
--- 133,144 ----
       */
      public boolean hasMethodHandles() {
          return hasInvokedynamic();
      }
  
+     /** Does the target JDK contain StringConcatFactory class?
+      */
+     public boolean hasStringConcatFactory() {
+         return compareTo(JDK1_9) >= 0;
+     }
+ 
  }