How does abstraction helps in hiding the implementation details in Java?

Question

Abstraction is a process of hiding the implementation details and showing only functionality to the user.

Another way, it shows only important things to the user and hid

Answer 1

The abstraction in your code is the abstract class itself:

abstract class Bank {    
   abstract int getRateOfInterest();    
} 

and the rest is the implementation (and the implementation details), specifically: classes PNB and SBI

But the thing i didn't understand is how it is hiding the implementation details?

Imagine you have a bank comparison engine, which is represented by the BankComparisonEngine class. It will just take a Bank (abstract class) as an argument, then get its interest rate and save it to its internal database, like so:

class BankComparisonEngine {
  public void saveInterestRateOf(Bank bank) {
    int rate = bank.getRateOfInterest();
    // Save it somwehere to reuse later 
  }
}

How are the implementation details hidden exactly? Well, BankComparisonEngine does not know how getRateOfInterest() method of a concrete implementation of Bank works (that is: PNB.getRateOfInterest() or SBI.getRateOfInterest() is implemented). It only knows it is a method that returns an int (and that it should return an interest rate). The implementation details are hidden inside the concrete classes that extend abstract class Bank.