My doubt is in line 4 how can a TaxCalculator class be declared as field calculator

[karthikreddy]

[Paul]

So, every variable (or field) must have a certain type. it could be int, String or whatever and you declare it as follows;

String myString;
int number;

In the same way calculator is declared as a variable of type TaxCalculator and you declare it as

TaxCalculator calculator;

[karthikreddy]

Thanks Paul but if we declare datatype as a String we can only give " sentences" for int only numbers. what we can only declare as TaxCalculator

[Paul]

You can do all the things with calculator that the TaxCalculator class allows you to do. So if it has eg a calculateTax method you can call it using calculator.calculateTax().