java update arraylist object

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Learn Java arraylists in 9 minutes! 📃 - YouTube

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Java Code Geeks

javacodegeeks.com › home › core java

Java ArrayList Insert/Replace At Index - Java Code Geeks

January 2, 2022 - We can use the set() for any type of object such as wrapper classes, String or any user-defined custom objects. It is allowed to update the values of the array list based on the condition while iterating it with the help of set() method.

w3resource

w3resource.com › java-exercises › collection › java-collection-exercise-5.php

Java - Update specific array element by given element

May 21, 2025 - Write a Java program to update an array element by the given element. ... import java.util.*; public class Exercise5 { public static void main(String[] args) { // Creae a list and add some colors to the list List<String> list_Strings = new ArrayList<String>(); list_Strings.add("Red"); list_Strings.add("Green"); list_Strings.add("Orange"); list_Strings.add("White"); list_Strings.add("Black"); // Print the list System.out.println(list_Strings); // Update the third element with "Yellow" list_Strings.set(2, "Yellow"); // Print the list again System.out.println(list_Strings); } }

How to do in Java

howtodoinjava.com › home › collections framework › java arraylist › replace an existing item in arraylist

Replace an Existing Item in ArrayList

January 12, 2023 - Once we have the index, we can use set() method to update the replace the old element with a new item. Find the index of an existing item using indexOf() method. Use set(index, object) to update with the new item.

stackoverflow.com › questions › 10053078 › arraylist-how-to-modify-a-member-of-an-object

java - ArrayList - How to modify a member of an object? - Stack Overflow

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You can do this:

myList.get(3).setEmail("new email");

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Fixed. I was wrong: this only applies on element reassignment. I thought that the returned object wasn't referencing the new one.

It can be done.

Q: Why?
A: The get() method returns an object referencing the original one.

So, if you write myArrayList.get(15).itsVariable = 7
or
myArrayList.get(15).myMethod("My Value"),
you are actually assigning a value / using a method from the object referenced by the returned one (this means, the change is applied to the original object)

The only thing you can't do is myArrayList.get(15) = myNewElement. To do this you have to use list.set() method.

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how to update elements in ArrayList in java. - YouTube

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program of update Existing element in arrayList with following steps 1. find intex of element which we want to update in arraylist 2.update element with set ...

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codespeedy.com › home › how to modify element or elements of an arraylist in java

Modify ArrayList Elements Java Program - CodeSpeedy

September 26, 2023 - Java program to change any element in an ArrayList. We will use set() method to modify or replace aJny particular element of an ArrayList

GeeksforGeeks

geeksforgeeks.org › java › update-the-list-items-in-java

Java Program to Update the List Items - GeeksforGeeks

July 23, 2025 - public Object set(int index, Object element) Return Value: The element that is at the specified index · Exception Throws: IndexOutOfBoundsException This occurs when the index is out of range. index < 0 or index >= size() Below is the implementation to Update the List Items in Java: Java · // Java program to update the list items // Importing required classes import java.util.ArrayList; import java.util.List; // Main Class public class UpdateList { // Main driver method public static void main(String[] args) { // Creating a list of courses List<String> courses = new ArrayList<>(); // Adding c

Coderanch

coderanch.com › t › 375852 › java › update-Object-Child-Arraylist

How to update an Object within a Child Arraylist! (Java in General forum at Coderanch)

Great Dave! Thanks alot! Now i'm wondering if it's possible to only update 1 field in that Object? Instead of updating the whole Object back to the ArrayList, can i update just 1 field in that Object possibly? ie ((ArrayList) ara.get(i)).set(j,tarj=>nshr) ? where i would only update the nshr field?

stackoverflow.com › questions › 67184487 › how-do-you-update-an-array-list

java - How do you update an array list - Stack Overflow

Its just like you did in delete method of yours, ArrayList as a static method set(int position, Object obj) this will update the object on that position. ... There is no edit method in interface java.util.List.

stackoverflow.com › questions › 32993540 › update-specific-object-items-inside-arraylist-java

arrays - Update specific object items inside Arraylist java - Stack Overflow

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If you know the position of the element do only the following:

userList.get(index).setUsername("newvalue");

If not, you need to loop all the elements to find the element to update

for (User user : userList) {
    if (user.getUserId().equals(searchedId)) {
        user.setUsername("newvalue");
        break;  
    }
}

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In your case I think it's better using a Map instead of a List:

Map<Integer, User> userMap = new HashMap<Integer, User>();

User user = new User();
user.setUserId(1);
user.setUsername("user1");
userMap.put(user.getUserId(), user);

user = new User();
user.setUserId(2);
user.setUsername("user2");
userMap.put(user.getUserId(), user);

user = new User();
user.setUserId(3);
user.setUsername("user3");
userMap.put(user.getUserId(), user);

In this way, you can search directly for the userId you need:

User userToModify = userMap.remove(idToModify);
userToModify.setUsername("new name");
userToModify.setUserId(54);
userMap.put(user.getUserId(), userToModify);

If you need to find object only by one field (userId, in this case), a Map is far more efficient and easy to use (and to maintain).

stackoverflow.com › questions › 23981008 › how-to-replace-existing-value-of-arraylist-element-in-java

How to replace existing value of ArrayList element in Java - Stack Overflow

coderanch.com › t › 439819 › java › Updating-modifying-elements-ArrayList

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318

Use the set method to replace the old value with a new one.

list.set( 2, "New" );

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If you are unaware of the position to replace, use list iterator to find and replace element ListIterator.set(E e)

ListIterator<String> iterator = list.listIterator();
while (iterator.hasNext()) {
     String next = iterator.next();
     if (next.equals("Two")) {
         //Replace element
         iterator.set("New");
     }
 }

Coderanch

Updating/modifying elements in ArrayList (Beginning Java forum at Coderanch)

June 4, 2009 - The HashMap takes a unique key (your player name), and a value (your player Object). This way you can just code like this (pseudo): Get Player from HashMap with name="My name" if Player is null then create new Player and add to HashMap else if Player is not null then update Player stats That's a condensed version but changing your code from an ArrayList to a HashMap is not hard at all and will save you lots of time/energy.

stackoverflow.com › questions › 42658202 › how-can-i-update-my-array-list-data-values

java - How can i update my array list data values? - Stack Overflow

import java.util.ArrayList; import java.util.Random; public class Theatre { private ArrayList<Room> theatres; public Theatre(){ theatres = new ArrayList<Room>(); theatres.add(new Room("Theatre 1", 120)); theatres.add(new Room("Theatre 2", 180)); theatres.add(new Room("Theatre 3", 100)); theatres.add(new Room("Theatre 4", 120)); theatres.add(new Room("Theatre 5", 200)); theatres.add(new Room("Theatre 6", 180)); theatres.add(new Room("Theatre 7", 80)); theatres.add(new Room("Theatre 8", 50)); theatres.add(new Room("Theatre 9", 120)); theatres.add(new Room("Theatre 10", 150)); } public void addTh

reddit.com › r/javahelp › how do you update elements of an array list that are processed from other methods?

r/javahelp on Reddit: How do you update elements of an Array List that are processed from other methods?

March 19, 2022 -

This is a continuation of this post.

I created a constructor employeePayReport. In that constructor I made an Array List whose each elements contain different methods of the Employee Class. My Employee Class is parent class and I have 3 child classes for it. I created an object, employeePayReport, in my main method, then I call different methods that would update the elements of ArrayList. I am getting an error while updating them and I am also struggling with how to store them.

Here is the code.

Question 1 (from your code): You have a member variable called console. This is available everywhere in your employeePayReport class. You don't have to pass it. The function already knows about it. Just go ahead and use it. This is because console is inside the class's scope. For the other questions, did you want to go with the idea I had in the previous post of putting more functionality in the Employee class and letting them handle their own details? If not, then I'll try to help you with the approach that you are choosing. Please let me know.

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reddit.com › r/javahelp › how to change the object in an arraylist ?

r/javahelp on Reddit: How to change the object in an arraylist ?

December 6, 2022 -

Hi, I'm not at all familiar with ArrayLists in java but I need to use them for this code and really need help. There's my code, I only translated the comments so that's what it does :

fill the terrain with ressources (sprout) : adds m (set at 10) sprouts into an arraylist. They are defined through the class Ressource that takes a name (set at the sprout emoji) and an amount set at 0 for the sprout because there's nothing to collect yet. Then they get randomly placed it an 10*10 tab (the println just say whether or not the object was successfully placed) then t.affiche displays the tab
make ressources grow (roses) : now that's the one I need help with, from what I researched list.set seemed to be the way to go about changing the elements but their ids are changing and therefore they don't appear in tab. I'm going to put some kind of randomizer on it but if it keeps the id it should just appear in the tab without me having to manually set it's position right ? Could anyone tell me how I could do that ?

ArrayList<Ressource> list= new ArrayList<Ressource> ();
		int m = 10; //nb of Ressource

//********************* fill the terrain with ressources (sprout)*******************

		 for (int i=0; i<m; i++){
		 	list.add(new Ressource(" 🌱 ",0));
		 	if (t.setCase((int)(Math.random()*(9)),(int)(Math.random()*(9)),list.get(i)))
			System.out.println("Ajout de " + list.get(i) +" valide !");
			else
			System.out.println("Ajout incorrect: problème de coordonnées !");
			
		}
		System.out.println(list);
		t.affiche(5);
		
		System.out.println("Informations sur le terrain:\n"+t);


//********************* make ressources grow (roses)*******************************

		for (int i=0; i<m; i++){
			list.set(i, new Ressource(" 🌹 ",(int)(Math.random()*(3)));
		}
		t.affiche(5);

As usual, your problem most likely lies outside the snippet you posted. You have the affiche method that you call - show its contents. Snippets of code are always problematic. In a very high percentage, the problem lies outside the posted snippet.

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From what I read the ArrayList serves no purpose in your code. It seems like you are adding a ressource into your t object via the setCase method. This object holds the resources used when calling the affiche method. Your second for loop just modify your ArrayList, but it has no link to the tobject, which still contains the resources set from the previous loop. Edit: if you want you can PM me the homework instructions, maybe this will make it more clear why you should use an ArrayList. I can speak French so no need to translate.

stackoverflow.com › questions › 54416960 › updating-specific-attribute-of-an-arraylist-item › 54417059

java - Updating specific attribute of an ArrayList item - Stack Overflow