ArrayList Retrieve object by Id

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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.

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.

ArrayList get() method, get(int index) method returns the element at the specified position 'index' in the list. 1.1. get() method syntax. indexOf() method. public Object  Retrieve an element from ArrayList in Java Java 8 Object Oriented Programming Programming An element can be retrieved from the ArrayList in Java by using the java.util.ArrayList.get () method. This method has a single parameter i.e. the index of the element that is returned.

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.

How to Find an Element in a List with Java, List<Customer> customers = new ArrayList<>(); implementation of equals, two Customer objects with the same id will be considered equal. Learn how to get the element from an ArrayList. We will be using ArrayList.get () method to get the object at the specified index of the arraylist. 1. ArrayList get () method. ArrayList.get (int index) method returns the element at the specified position 'index' in the list.

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);

How do I know if an ArrayList contains a specified item?, How do I check if an ArrayList contains an object? Java Collection, ArrayList Exercises: Exercise-4 with Solution. Write a Java program to retrieve an element (at a specified index) from a given array list.

ArrayList does not sort the elements contained. If you want to look for a single element in an ArrayList, you're going to need to loop through the list and compare each one to the value you're looking for.

Account foundAccount;
for(Account a : accountList){
  if(a.Id == targetID){
     foundAccount = a;
     break;
  }
}
if(foundAccount != null){
  //handle foundAccount
}
else{
  //not found
}

Alternatively, you can use a more intelligent data structure which does sort and keep information on the data contianed.

You'll want to research the Map interface, specifically the HashMap implementation. This lets you store each element in an order tied to a certain key. So you could place each of your objects in a HashMap with the Id as the key, and then you can directly ask the HashMap if it has an object of a certain key or not.

ArrayList get(index) method in Java with examples, ArrayList get(int index) method is used for fetching an element from the list. We need to specify the index while calling get method and it returns the. First of all it's not working, and I can't see why. I'm while-looping through (potentially) all the objects in the arraylist, for then after the loop is finished, checking whether the loop finished because it ran out of objects to search through, or because it found an object with the given ID.

You must use the Map for example:

private Map<String, int> AccountMap;
for (String account : accounts )
             AccountMap.put(account, numberofid);

Java ArrayList Index, public E get(int index). The ArrayList.get() method is used to get the element of a specified position within the list. Package: java.util. Java  If you use Java 8 and if it is possible that your search returns null, you could try using the Optional class.. To find a carnet: private final Optional<Carnet> findCarnet(Collection<Carnet> yourList, String codeIsin){ // This stream will simply return any carnet that matches the filter.

Java ArrayList get() Method example, The get() method of ArrayList in Java is used to get the element of a specified index within the list. Syntax : get(index). Parameter : index:index of the elements to  If you want to use the plain old javascript you can create a function that iterates over the array and then return the object when the id matches with the one you’re looking for (or return null

Java arraylist get method, The size, isEmpty, get, set, iterator, and listIterator operations run in constant time. The add If no such object exists, the list should be "wrapped" using the  Object.equals is a virtual method defined for all object instances and it means "has the same value", as all class types extend Object, and should be used for all object-equality tests. There are many questions at cover == vs Object.equals and this is a very important concept to understand! For instance, this is false: "hello" == new String

ArrayList, Declaring the ArrayList, note the use of the syntax "<Particle>" to to fill this ArrayList with Particle objects ArrayList<Particle> particles = new pulled out of an ArrayList with get() Particle part = particles.get(0); part.display();  I'm working on some legacy code, so cannot use Generic List here. I have an ArrayList being returned from a data layer method. Each item in the last consists of an ID and a Description field. I want to loop through the ArrayList and search for a match on the Description string - any ideas? Format. ID DESCRIPTION 1 SomeValue I know I can do this:

Comments
  • Use a Map or iterate over all the elements in the ArrayList.
  • use map (HasMap) or set(HashSet) instead
  • Only hash-based maps will give you O(1) lookups.