Naveen Bachu

It's still mislabeled as "the best way" at best, falsely advertised at worst. Don't use that method, even with synchronization. There are better ways.

I didn't get what is wrong with the code, except synchronization, Can you guide us to any best example to compare and improve our knowledge?

This will still work by adding synchronized block

This implementation seems to be very poor, we create Singleton class so that no one should be able to create two instances Note: this rule is also applicable for the person who is writing this class

Here is the example which explains about implementation of Singleton class: Best Way to Create Singleton Class

Ishan Pandya is correct, either you can use normal for loop or foreach to iterate all the elements of the arraylist.

Here is the example for your reference How to Use ( Java ) For Loop with ArrayList