Help with accessing a get method without causing a stackoverflow error

Question

First I just did arrObj[countOne].getExtended, but it says getExtended does not exist in the
Stock class and suggests me to make one ( but it has to be in the Etf class ). So I created an object etf in the Stock class (Etf etf = new Etf()) and did
etf.getExtended() . but this causes a stackoverflow error.

https://code.sololearn.com/WvtIjxxs6A5o/#js