An object is only once in memory. Your first addition to list just adds the object references.
anotherList.addAll will also just add the references. So still only 100 objects in memory.
If you change list by adding/removing elements, anotherList won't be changed. But if you change any object in list, then it's content will be also changed, when accessing it from anotherList, because the same reference is being pointed to from both lists.
Top answer 1 of 5
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An object is only once in memory. Your first addition to list just adds the object references.
anotherList.addAll will also just add the references. So still only 100 objects in memory.
If you change list by adding/removing elements, anotherList won't be changed. But if you change any object in list, then it's content will be also changed, when accessing it from anotherList, because the same reference is being pointed to from both lists.
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100, it will hold the same references. Therefore if you make a change to a specific object in the list, it will affect the same object in anotherList.
Adding or removing objects in any of the list will not affect the other.
list and anotherList are two different instances, they only hold the same references of the objects "inside" them.
DigitalOcean
digitalocean.com › community › tutorials › java-list-add-addall-methods
How To Use add() and addAll() Methods for Java List | DigitalOcean
September 10, 2025 - ArrayList: O(1) amortized for add(E), O(n) for add(int, E) due to element shifting · LinkedList: O(1) for both variants, but with higher constant overhead due to node creation · Vector: Similar to ArrayList but with synchronization overhead ... package com.journaldev.examples; import java.util.ArrayList; import java.util.LinkedList; import java.util.List; public class ListAddExamples { public static void main(String[] args) { // Example 1: Basic add() operations List<String> vowels = new ArrayList<>(); vowels.add("A"); // [A] vowels.add("E"); // [A, E] vowels.add("U"); // [A, E, U] System.ou
What is the best way to add items to a list?
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April 22, 2022Add elements of a list to the same list in java - Stack Overflow
But it is not guaranteed to. The Javadoc for addAll says: The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified collection is this list, and this list ... More on stackoverflow.com
Is there a way to add elements to an Array List all at once?
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November 2, 2021How to add gentoo-vm USE flag?
Normally I would add dev-java/openjdk gentoo-vm to /etc/portage/package.use/openjdk but emerging the package again shows me that the flag has not been set. Any difference I miss when using experimental USE flags? ... Thank you very much. That did the trick! ... How great it would have been if the answer was still here... :( ... jbootstrap is enabled. However eselect java-vm list ... More on reddit.com
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April 30, 2020What is a linked list in Java?
A linked list in Java is a data structure that consists of a sequence of elements, each contained in a node. Nodes are chained together using pointers, with each node pointing to the next node in the sequence. The use of pointers allows for efficient insertion and deletion of elements as it does not require shifting elements, which is required when relying on simple arrays.
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Tutorial: Learn how to add elements to a Java List now! 🚚
What is a linked list node in Java?
A linked list (java.util.LinkedList) node in Java is a basic element of a linked list data structure, consisting of two main components:
- The data part that stores the element's value, and
- a reference (or pointer) to the next node in the sequence, facilitating the link in the list.
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Tutorial: Learn how to add elements to a Java List now! 🚚
What are linked lists good for in Java?
Linked lists in Java (java.util.LinkedList) are useful in scenarios where frequent insertion and deletion of elements is required, as these operations can be performed more efficiently than in arrays, because there's no need to shift elements. Linked lists (java.util.LinkedList) are also useful when the size of the data structure needs to be dynamically allocated.
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Tutorial: Learn how to add elements to a Java List now! 🚚
Videos
GeeksforGeeks
geeksforgeeks.org › java › list-add-method-in-java-with-examples
List add() Method in Java with Examples - GeeksforGeeks
July 11, 2025 - How to add an element to a list in Java using the add(Element E) method:
Reddit
reddit.com › r/javahelp › what is the best way to add items to a list?
r/javahelp on Reddit: What is the best way to add items to a list?
April 22, 2022 -
using stream API
ArrayList<Integer> list= Stream.of(1,2,3).collect(Collectors.toCollection(ArrayList::new));
or without it
ArrayList<Integer> list1=new ArrayList<>(); list1.add(1); list1.add(2); list1.add(3);
Top answer 1 of 7
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If you want to create an unmodifiable list and you know the items to be added to the list, you can create it like the below: List integers = List.of(1, 2, 3); If you want to create a modifiable list with some default values, then you can create it like the below: List integers = new ArrayList<>(List.of(1, 2, 3));
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I think people forget the purpose of Streams, because they allow devs to apply functional programming principles to Java code. To directly answer your question, I wouldn't use a Stream specifically in this case. Initiate a plain ArrayList. Add the numbers. Call it day. Note that it isn't inherently wrong to use the first version, so feel free to do so. Have a look at the Wikipedia article and the JavaDoc on streams to learn where some of these ideas come from. I think that can help inform devs on whether or not (readability withstanding) the Stream API is a good idea.
iO Flood
ioflood.com › blog › java-list-add
Adding Elements to a List in Java: A How-To Guide
February 27, 2024 - In this example, we create a new ArrayList and use the add() method to insert the string ‘Hello’ into the list. The output shows that the list now contains one element: ‘Hello’. This is a basic way to use the add() method in Java, but ...
TutorialsPoint
tutorialspoint.com › article › how-do-i-insert-all-elements-from-one-list-into-another-in-java
How do I insert all elements from one list into another in Java?
June 13, 2025 - We can use a ListIterator to traverse the source list and add each element to the destination list. In the following example, we will create a source list and a destination list, and then use a ListIterator to insert all elements from the source list into the destination list. import java.util.ArrayList; import java.util.List; import java.util.ListIterator; public class InsertAllElements { public static void main(String[] args) { List<Integer> sourceList = new ArrayList<>(); sourceList.add(1); sourceList.add(2); sourceList.add(3); List<Integer> destinationList = new ArrayList<>(); destinationL
Thospfuller
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Tutorial: Learn how to add elements to a Java List now! 🚚
May 27, 2025 - In this Java Code Example, we’ll learn how to add elements to a List in Java via the constructor, by invoking the add and addAll methods, by calling the addFirst and addLast methods, and finally by invoking the push method.
Python Examples
pythonexamples.org › java › how-to-append-a-list-to-another-list
How to Append a List to another List in Java
Finally, we print the updated list1 to standard output. import java.util.ArrayList; import java.util.List; import java.util.stream.Collectors; public class Main { public static void main(String[] args) { List<Integer> list1 = new ArrayList<>(); List<Integer> list2 = List.of(4, 5, 6); list1.addAll(list2.stream().collect(Collectors.toList())); System.out.println("Updated list: " + list1); } }
Jenkov
jenkov.com › tutorials › java-collections › list.html
Java List
By default you can put any Object into a List, but from Java 5, Java Generics makes it possible to limit the types of object you can insert into a List. Here is an example: ... This List can now only have MyObject instances inserted into it. You can then access and iterate its elements without casting them. Here is how it looks: List<MyObject> list = new ArrayList<MyObject>(); list.add(new MyObject("First MyObject")); MyObject myObject = list.get(0); for(MyObject anObject : list){ //do someting to anObject...
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The addAll method of ArrayList happens to work in Oracle's JDK (and OpenJDK). But it is not guaranteed to. The Javadoc for addAll says:
The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified collection is this list, and this list is nonempty.)
The question is actually not as pointless as some of the answers imply. Just "trying it" is not a sufficient test that something works correctly, as this case proves.
In fact, when thinking about whether list.addAll(list) works, you need to ask yourself how it might be implemented. If it was simply iterating over list and adding each element to the end of list, you'd get a ConcurrentModificationException (or else it would go into an infinite loop). That's why the Javadoc doesn't guarantee that such a call works. As it happens, Oracle's implementation copies the passed list to an array first, and then copies each element of the array to the end of the list. This means that calling addAll for a list might not be as efficient as doing it yourself without creating an extra copy.
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The main drawback with myList.add(myList); is that it won't compile, because myList isn't an Integer.
You can, however, use:
myList.addAll(myList);
Ideone demo
or
myList.addAll(new ArrayList<>(myList));
if you want to do it safely.
JavaBeat
javabeat.net › home › list of lists in java: how to create, iterate, and access it
List of Lists in Java: How to Create, Iterate, and Access it
March 20, 2024 - Since, each element of a list of lists is also a list, so we use the asList() method three times to add three lists as elements of the exampleLists. On successful execution, you will get the following output on the console: Alternatively, you ...
Coderanch
coderanch.com › t › 676345 › java › access-add-element-list-lists
How to access and add an element to a list of lists [Solved] (Beginning Java forum at Coderanch)
February 19, 2017 - I aim to print a list of lists containing entry and exit times in the 24 hour decimal format from the "AM"-"PM" String format input by the user as a String array like this: 6AM#8AM 11AM#1PM 7AM#8PM 7AM#8AM 10AM#12PM 12PM#4PM 1PM#4PM 8AM#9AM I declared the individual lists inside the for loop and assigned them values inside the loop but again got the following run time exception from my code: java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
Runestone Academy
runestone.academy › runestone › static › JavaReview › ListBasics › listAdd.html
9.11. Adding Values to a List — AP CSA Java Review - Obsolete
This would be true if the add(2, new Integer(4)) replaced what was at index 2, but it actually moves the value currently at index 2 to index 3. You can step through the code above by clicking on the following Example-8-5-1. 8-5-5: What will print when the following code executes? List<String> list1 = new ArrayList<String>(); list1.add("Anaya"); list1.add("Layla"); list1.add("Sharrie"); list1.add(1, "Sarah"); System.out.println(list1);
Baeldung
baeldung.com › home › java › java list › working with a list of lists in java
Working With a List of Lists in Java | Baeldung
April 3, 2025 - Then, we add the new list to listOfLists in the position with index=2. Again, after the assertions, we print the content of listOfLists: List of Lists ------------------------------------- Linux, Microsoft Windows, Mac OS, Delete Me Kotlin, Delete Me, Java, Python Slack, Zoom, Microsoft Teams, Telegram Delete Me, Mercurial, Git, Subversion
Reddit
reddit.com › r/javahelp › is there a way to add elements to an array list all at once?
r/javahelp on Reddit: Is there a way to add elements to an Array List all at once?
November 2, 2021 -
For example I can do this with a basic integer array:
int[] test1 = new int[]{2, 1, 5, 1, 3, 2};But with an Array list I have to add them one at a time like this
List<Integer> test1 = new ArrayList<Integer>(); test1.add(2); test1.add(1); test1.add(3);
?
Top answer 1 of 4
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If you know your values before hand you can do List.of(x, y, z,...); Note that this will give you an immutable list
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There are many ways, here are some I find most elegant: List list1 = new ArrayList<>(List.of(1, 2, 3, 4)); // or List list2 = new ArrayList<>(Arrays.asList(1, 2, 3, 4));
W3Schools
w3schools.com › java › ref_arraylist_add.asp
Java ArrayList add() Method
Java Data Structures Java Collections ... Java List Sorting Java Set Java HashSet Java TreeSet Java LinkedHashSet Java Map Java HashMap Java TreeMap Java LinkedHashMap Java Iterator Java Algorithms · Java Wrapper Classes Java Generics Java Annotations Java RegEx Java Threads Java Lambda Java Advanced Sorting ... How Tos Add Two Numbers ...
Coderanch
coderanch.com › t › 682316 › java › adding-List
adding to a List (Beginning Java forum at Coderanch)
July 19, 2017 - Instead, it returns a special implementation of interface List that reflects what is in the array that you created the list from. This special implementation of List does not allow elements to be added to it - that's why you get an UnsupportedOperationException when you try to call the add(...) method on it.
Baeldung
baeldung.com › home › java › java collections › add multiple items to an java arraylist
Add Multiple Items to an Java ArrayList | Baeldung
January 8, 2024 - One of them is addAll, which needs a destination list and the items to be added may be specified individually or as an array.
How to do in Java
howtodoinjava.com › home › collections framework › java arraylist › java arraylist add() – add a single element to list
Java ArrayList add() - Add a Single Element to List
August 7, 2023 - The ArrayList.add() in Java adds a single element to the list, either at the end of the list or at the specified index position. Always use generics for compile-time type safety while adding the element to the arraylist.
How to do in Java
howtodoinjava.com › home › collections framework › java arraylist › java arraylist.addall() – add multiple items to a list
Java ArrayList.addAll() - Add Multiple Items to a List
August 7, 2023 - The addAll() is one such method to add multiple elements in a single statement. Although, if generics are not used, it is the programmer’s responsibility to ensure that the argument collection has the same type of elements as in the current arraylist. Happy Learning !! ... A fun-loving family man, passionate about computers and problem-solving, with over 15 years of experience in Java and related technologies.