ArrayList Retrieve object by Id

Java Solution:

Account account = accountList.stream().filter(a -> a.getId() == YOUR_ID).collect(Collectors.toList()).get(0);

Kotlin Solution 1:

val index = accountList.indexOfFirst { it.id == YOUR_ID }
val account = accountList[index]

Kotlin Solution 2:

val account = accountList.first { it.id == YOUR_ID }

Assuming that it is an unordered list, you will need to iterate over the list and check each object.

for(int i = 0; i < sizeOfList; i++) {
    list.get(i).equals(/* What you compare against */)
}

There's also the other for syntax:

for(Account a : accountList)

You could put this loop into a helper method that takes an Account and compares it against each item.

For ordered lists, you have more efficient search options, but you will need to implement a search no matter what.

It sounds like what you really want to use is a Map, which allows you to retrieve values based on a key. If you stick to ArrayList, your only option is to iterate through the whole list and search for the object.

Something like:

for(Account account : accountsList) { 
   if(account.getId().equals(someId) { 
       //found it!
   }
}

versus

accountsMap.get(someId)

This sort of operation is O(1) in a Map, vs O(n) in a List.

I was thinking of extending ArrayList but I am sure there must be better way.

Generally speaking, this is poor design. Read Effective Java Item 16 for a better understanding as to why - or check out this article.

A better way to do this would be to use a Map.

In your case, you could implement it in the following way

    Map<account.getId(), account>

you can use the "get" method to retrieve the appropriate account object.

    accountMap.get(id);