ArrayList Retrieve object by Id

Question

Suppose I have an ArrayList<Account> of my custom Objects which is very simple. For example:

class Account { public String Name; public Integer Id; } 

I want to retrieve the particular Account object based on an Id parameter in many parts of my application. What would be best way of going about this ?

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

Answer 1

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.

Answer 2

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 }