The code example in ScriptEngineFactory.getProgram uses string concatenation is a subopotimal way:

 public String getProgram(String... statements) {
      String retval = "<?\n";
      int len = statements.length;
      for (int i = 0; i < len; i++) {
          retval += statements[i] + ";\n";
      }
      return retval += "?>";
 }

A StringJoiner would yield concise code and likely be more efficient too.