How to iterate and modify list in java. removeAll(Collections.

How to iterate and modify list in java Possible Duplicate: Best way to iterate through a directory in java? I want to process each file in a certain directory using Java. Iterate ArrayList. Iterate, instead, on the list with the items that have the criteria to be removed: lis = Can't believe that there is no more simple and secured solution instead of using an iterator in this answers JSONObject names method returns a JSONArray of the JSONObject keys, so you can simply walk though it in loop:. I have started iterate original list [1, 4, 5], I am between 1 and 4. ListIterator is an iterator for list that can traverse the list in either Fortunately, Java provides a variety of ways to loop through a list, from classic loops to more modern and functional approaches. ArrayList; import java. servers); and use that as the list for the foreach-loop. I need to be able to first filter out the keys with even numbers then iterate the map values and modify the content of map values. There is no break-condition. Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. First you need to understand why it doesn't change the value of item. The Overflow Blog “Data is the key”: Twilio’s Head of R&D on the need for good data Possible Duplicates: Java: Efficient Equivalent to Removing while Iterating a Collection Removing items from a collection in java while iterating over it I'm trying to loop through HashMap: Iterator. spliterator(), false) . What I would like to know is to modify the elements containing in the Set. The stream pipeline will not be invoked unless you attach a terminal operation to it. Update element in You use the Iterator to remove entries as you come upon them. Map<Integer, Emp> empData = emp. [They] let you manipulate their underlying counterparts reflectively. Modifying original List throws CMEx : While iterating List/ArrayList, if we try to modify original List like adding/removing elements then program throws How to iterate over Array List and modify elements inside the object in Java? Ask Question Asked 3 years, To iterate the list I can by following: Modifying each item of a List in java. Could you help me out I'm new to Java and I want to ask how this could be done and if this is the right approach. Follow edited May 15, 2011 at 8:51. xssf. public class LargeDTO extends CoreDTO { private List<BigDecimal> prices; public LargeDTO() { prices = new ArrayList<BigDecimal>(); } //getter and setter for your prices } //in I need to iterate over this Hash Map object, while iterating we need to check the condition i. list*() functions. @Bob. 707Explanation: Here, we Java ListIterator::remove which documents "This call can only be made once per call to next or previous" To put in a simpler way: do not iterate on the list you're trying to change. This returns null, because you've not setup mockito to Assuming Java 8 and considering the fact that feedbackStatus may contain more than one element with the same ID. 50. remove() and concurrent collections. I don't know what your Card class looks like but there is nothing wrong with the following:. java; list; arraylist; iterator; or ask your own question. What you are modifying is the elements in the list; That is perfectly fine. The call to add() on the mocked list effectively doesn't do anything. from last to first element. class); to check if one type belongs to family of some ancestor (like List is subtype of Collection) use isAssignableFrom like . Now how to iterate the list of objects and get the values from this objects. Modifier. Pretty new to Java here. Review different ways to iterate through a List in Java. Iterable<Element> iterable = createIterable(); List<Element> array = StreamSupport . protected Map<String, Object> objects = new HashMap<String, Object>(); Once that's fixed, I think this is what you meant: I am trying to iterate a ArrayList and add to another ArrayList using jboss drools inside the rule. JAVA loop through children of Nodelist. The enhanced for loop doesn't let you change the values of what you're iterating over. To safely update items in the list, use map(): List<String> letters = new ArrayList<>(); // add stuff to list letters = letters. Modify objects while iterating 2 Lists using java stream. JSONObject object = new JSONObject (); JSONArray keys = object. remove() 2. ListIterator" classes In Java, can you modify a List while iterating through it? 1. List<Card> cardList = new ArrayList<>(); for (MerchantGatewayEntitlement Basics of Iterating a List in Java. – First things first. val = val; } public int getVal() { return val; } } public I was wondering, How can we iterate a multilevel list using stream API in Java 8 For example, List<List<String>> multiList = new ArrayList<>(); List<String> names= Arrays. forEach() method with lambda expression to iterate over a list. This implementation returns a straightforward implementation of the iterator interface, relying on the backing list's size(), get(int), and remove(int) methods. *; public class QueueLinkedList<Customer> implements Queue<Customer>, Iterable<Customer> { Node first, last; public class Node { Customer ele; Node next; } class Iter implements However, this is dangerous way to do. You know, there are several ways to iterate collections in Java, but using iterator is the most basic and original. set(j, 0); //sets the element at j to be 0, notice the values are Int not int, this is dues to Javas generics having to work with classes not simple types, the values are It depends on how often you need to perform this logic on your input data. You can also transform your List into a Map using a Stream:. As I iterate over the graph nodes and found a certain node in the adjacency list of the iterated node, I need to update the connected component num. How to modify an element in Array list. I am coming from Python. Map<Integer, MyObject> map = list. Loop through the list items; find the <a> tags and change their color and background; Upon exiting the loop, change the color and the background of the HTML element that caused the event. Viewed 2k times 1 . The reason is that Integer is an immutable class, meaning that once the class instance is assigned a value (int) it won't change. Modified 4 years, 1 month ago. Deleting and adding objects to list while iterating. copy() method. remove() } Are there any reasons to prefer one approach over the other (e. isTransient(field. These are excerpts from the book: Given a Class object, you can obtain Constructor, Method, and Field instances representing the constructors, methods and fields of the class. would make it more efficient that a traditional loop, except if you plan on running parallel streams. class SkippingIterator<T> implements Iterator<T> { private List<T> list; private currentPosition; private int skipBy; public 2. remove:The behavior of an iterator is unspecified if the underlying collection is modified while the iteration is in progress in any way Ideal for simple iteration through a list when you don’t need to modify the list elements. Modifying a list of objects in java. stream(). Depending on exactly what it is you are doing, you may be able to do the following while iterating: use the Iterator. to iterate list use for example for each: for (Tuple tuple : queryResult){ 'put code and assertion here' } Share. getValue(); // do stuff } I have a JSON file with some arrays in it. import java. I am currently stuck on a JSP page. 707]Output: Using for loop:3. Java, adding modified string to ArrayList with foreach loop. Java Adding items to ArrayList while iterating it. Now I would I have a set of strings that I'd like to iterate over, and change all of those who equal something, to equal something else: // Set<String> strings = new HashSet() for (String str : strings) Skip to main content Java: change an element in a prepopulated List of string array. Modified 8 years, 1 month ago. There are similar questions on SO talking about remove or add element while iterating a Java Set. I also would like to iterate in a way that let me choose whether I want to iterate horizontal There are two issues here: The first issue is, adding to an Collection after an Iterator is returned. Collections documentation: public static <T> Enumeration<T Iterating on list with stream in java 8. A ListIterator has no current element; its cursor position always lies between the element that would be returned by a call to previous() and the element that would be returned by a call to next(). The enhanced for loop is a simple structure that allows us to visit every element of a list. Updating elements in a ArrayList<List> 6. remove(). Hot Network Questions Convergence to a I know that it is not safe to modify the list during an iterative looping. Note there is a difference between Iterable and Iterator. How do I iterate through the array and actually change the values in the array. Nested lists with streams in Java8. At the start of the turn, iterate through the list and set "RUNTURN" to false on all elements Iterate through the list backwards, e. AbstractList class is used to return an iterator over the elements in this list in proper sequence. Say I have 2 parallel collections, eg: a list of people's names in a List<String> and a list of their age in a List<Int> in the same order (so that any given index in each collection refers to the same person). I dont understand what xyxy is in your code. Entry. Please help me here. previous(); // Do something with prev here } The initial index of the iterator should be equal to the index of the last element + 1. Implementing Iterator. XSSFSheet; import I want to iterate through all nodes of a json object, and write out a plain key-value map, as follows: { &quot;name&quot;: [{ &quot;first&quot;: &quot;John&quot;, &quot;last&quo Sure - but you can specify LinkedHashMap when creating the instance. Table The iterator() method of java. My interface is actually SortedSet – myborobudur. ss. Java XML How to - Use xpath to find and add/replace more children to a Nodelist in an XML file. Using a For Loop. 83. Now I want to write a method deleteEmployee(String, ArrayList<Employee>) which will compare the string given as the parameter with an employee List<List<Int>> arrayList = new ArrayList(); //Java usually infers type parameters in cases as these for(int i = 0; i < desiredSize; i++){ List<Int> listAtI = new ArrayList (); for(int j = 0; j < rowLength; j++){ listAtI. They are coming from a class Computer which extends from class Product. The idea I followed was: * List 1: [1 2] * List 2: [4 5] * List 3: [6 7] * * Take each element from list 1 and put each element * in a separate list. IOException; import java. You need to overwrite the entry in the list with a new object. Share. Hot Network Questions cross referencing of sections within a document The list is maintaining an object reference to the original value stored in the list. I want to ask how I can "reset" my iterator to the first element. I would like to iterate through two dimensional ArrayList which includes String objects using iterator. This power, however, comes at a price: An Iterator allows you to iterate through a List's elements. How to iterate through ArrayList of objects? 0. Java also provides the listIterator class, which can be used to traverse a list in both The reason why you cannot modify a list while iterating over it is because the iterator has to know what to return for hasNext() and next(). How to iterate the arraylist of diffrent objects. length (); i++) { String key = keys. ListIterator is an iterator for list that can traverse the list in either direction, can modify as well as can obtain the iterator's current position in the list. AOP frameworks allow you to add some code to the method without changing it. Entry<K,V> in the Map, or you can iterate through the key Set. keySet(); The collection used in foreach is immutable. In a kind of chat with a chatbot that I'm implementing, I have a List of Conversation and every Conversation has a List of Messages. You should be using a Map instead:. Best way to modify objects in list using values from another list. List<ServerObject> copyList = new ArrayList<ServerObject>(this. For other types of change, you may need to: create a new Map from the entries in the current Map, or A List is an order collection that can store elements of any type, including duplicates and null values. List keys = new The fix is to declare the type of object held by your array list. Iterate by two elements on a list with Java. DataFormatter; import org. isAssignableFrom(List. g: class Box<T> { public T boxed; } and then use a Dictionary<string, Box<double>> which you can then "modify" in the foreach something like: Learn how to prevent ConcurrentModificationException when modifying a Java List during iteration. The Dictionary class is way, way obsolete. getModifiers()) The only solution to directly manipulate the list using a Java Stream, is to create a Stream not iterating over the list itself, i. To do so you must use an iterator. I'm aware of the set() method of linked list but that operation is O(n). 2. The internal data structure should not be modified while iterating through the collection. Iterate the list and use the Map to find all messages. A Google search for copying a list suggested me to use Collections. And any Java programmers should be familiar with and fluent in using iterator. Improve this answer. 403k 96 96 Java Iterate Over List. put("Data", list); } This effectively maps the key "Data" to the value list, repeating this mapping several times, but you only have entry. EDIT: I dont think its a good idea to iterate the newly added element to a Hashmap. type. In Java, List is is an interface of the Collection framework. Effective Java 2nd Edition, Item 53: Prefer interfaces to reflection. removeAll(Collections. This implementation returns a straightforward In java 8 you can use List. When it comes to iterating a list in Java, there are several fundamental techniques that every programmer should be familiar with. – There is no multiple iteration. Android ArrayList of int. Fail-fast iterator read internal data structure directly . Java Enumeration for Iteration over Legacy Classes. remove() is safe, you can use it like this: List<String> list = new ArrayList<>(); // This is a clever way to create the iterator and call iterator. I want to iterate through the file arrays and get their elements and their values. For eg: remove all those elements where value is test, then use below:. Collections. Row; import org. For the object being run: If RUNTURN is Why use streams? It has its advantages but it also has quite a bit of overhead. I am using the ListIterator to add and the Iterator to delete because I read in a bunch of website that this is the only ways to add and delete and the change will take place directly in the arraylist but my problem is that it is adding and deleting and the arraylist count or reference number on the debugger looks fine but when I search through it I cant find the new. Provide details and share your research! But avoid . Iterator<Foo> itr = fooList. I know I can do it with map but that makes a copy of the list. e. So, apparently it seems that I need to update the set I am iterating over. poi. In addition, I would like to do it in place, i. list[:] = ["Modify the list" for each_element in list "Condition Check"] example: list[:] = [list. Commented May 21, 2015 at 9:04. How to do this? java; iteration; Share. iterator(); while(itr. I've searched a lot, but most of the examples are used to collect data from the array without modifying it. Method for modifying an element in an Array list? 0. out. However, using the interface name for the variable allows you to make the code implementation independent. 6180. apache. e if Key=DATE and it's value = "5/1/2020", then need to update/set other key's i. populate list of list in java. forEach(f -> f. I can iterate, like this: for list in game: for element in list: but to change the elements in my list of lists it's another story, I can create a new list with append, but I get something like [1, 2, 2, 0, 0, 2, 0, 0, 0] Either change the Map implementation into one of the ones that support ordering or sort the keys before iterating over them. As long as you don't directly change the actual list, you're fine. Modify During Traversal: When you want to modify while iterating over it. Java removing an iterator that removes another element in the same list. In this article, we will see how to iterate the float list in Python. But then it might be possible that an other thread appends a Server to the servers list while I am iterating over copyList but closeCurrentlyOpen is supposed to result in an emtpy list. There are some fundamental issues why your example not does work and throws a NullPointerException. If you want to modify your List during traversal, then you need to use the Iterator. Java 5 and up). entrySet()). However, suppose I have a list of strings, and I want to strip the strings themselves. Whether or not the array needs to be a new array or just mutated was kind of secondary, I really just wanted to see if there was a more declarative way to write what I seem to do a lot, in my current project. Collection. List<String> listA = new Arraylist(); List<String> listB = new Arraylist(); Given above 2 lists, I want to iterate and call the same method on each element. 618, 0. Extension isn't always the preferred mechanism, but it depends on what you're actually doing. next(); Both x and the list are storing a reference to the same object. How to go through 2 lists and do a check. findAny() on the other hand, will stop after the first user was found. I add the objects to an object list, now I need to get the Shelfnumbers (the last value in the objects) from each object and add a different amount to them depending on what the You are iterating two streams synchronously and author wants to iterate all the values of listB list for every value of listA. java"} Share. I am assuming that you will not need to iterate newly added value as it wont make much sense. Change the declaration to: ArrayList<Node> filled_data_ = new ArrayList<>(); Java Iterate Over List. Modifying list object in java. stream creating List of List (nested List) using forEach, Java 8. However, incase I add while iterating then I just start the iteration from fresh by breaking out of iteration loop & restarting iteration from beginning. Each employee has some attributes (name, dob, designation, salary) and I store them in an ArrayList. equals(List. it does not implement RandomAccess), then using an Iterator (or an enhanced for-loop, which uses an Iterator internally) instead of a traditional for-loop is usually much more efficient. A ListIterator has no current element; Ways to iterate over a list in Java. Why using This class is broken, because the user might want to iterate a second time over the same Iterable, or the list might change between when the iterable is constructed and when it's iterated. I want to copy/clone the contents of that list into an empty list of the same type. Iterator iterator = java. entrySet()) { var key = entry. util. Explore safe methods like Iterator. getName()); } Share. Table of content: 1. And then iterate over that list to get each Person instance back: - for (Person person: personList) { System. For example, you could conditionally remove or add elements based on specific criteria, like eliminating all students who are not enrolled. You could only use foreach then, but then it's not possible to modify the list in the loop. Class DroolsPojo{ List<String> answers; //getters and setters } I have a little problem with ListIterator. Commented Mar 16, 2012 at 16:21. What is the easiest (and most common) way of doing this? You can change null and put a list of extentions if you wanna filter. collect(Collectors. set( 3, new Customer( "Doe", "[email protected]" ) ); But that means creating a new object. class) to check modifiers of field like transient use. getName() + "s")) Share. – I am using a set of graph nodes and the nodes have id and an attribute connected Component number. It’s similar to the basic I need to iterate over all vlaues contained within each List within the Map. I'd doubt using streams etc. remove() to remove the elements during traversal. Follow How to change `List` to `List of tuple` in java. Method for modifying an element in an Array list? 1. Enumeration interface is the legacy interface available since JDK1. This does something similar, without an iterator-based approach. In Java, a list can store another list as its element, which is referred to as a List of lists, nested list, or 2D list. Java iterate a list and add to object containing a list. In all the examples I saw, the destination list was supposed to contain the exact number of items for the copying to take place. usermodel. One point to keep in mind, 'though: If listToTrim is not a random-access-list (i. Entry<K,V>. Create your own Iterator. There are two important methods of this Enumeration interface. You can check the java doc for the "java. Hot Network Questions Why does the MS-DOS 4. Iterator; The above snippet shows how these two can be used to iterate over the list. So I have a Deck class which holds a deck list which creates 52 Card objects and stores them in an array list. Hot Network Questions Why did the sw- in PIE *swenh₂ (to sound) change to zv- in Proto-Slavic *zvoniti (to ring), but sw- in *swéḱs (six Nothing in that answer discourages extending ArrayList; there was a syntax issue. println(crunchifyIterator. replaceAll(UnaryOperator<E> operator) since Java 8. Java 10 simplified that by letting variable types be inferred using var: for (var entry : map. This means that generally you can't modify a set element in-place like you're doing with the list. println(person. If you have many slots and few matches there might be other This guide covers various methods to iterate over List, Set, and Map collections, including examples using Java 8 features. remove I've a class Employee and a method in that class as getName() which returns the name of the employee. 5. hasPrevious()) { String prev = listIter. In Java, can you modify a List while iterating through it? 0. If you have many slots and few matches there might A map is an intermediate operation. Modify list items selectively using stream. All void methods on mocks are "no-ops" by default; Iterating over a list using for-each syntax calls Collection. Update all the elements of a list without loop. preferring the first approach for the simple reason of There is also List. These options included the for loop, enhanced for loop, Iterator, ListIterator, and the forEach() method (included in In this article, we will learn to iterate list in our Java application. previous year events also get appended. forEach: fruits. how to use Iterator in object arraylist. It provides us to maintain the ordered collection of objects. Iterator" and "java. The The task you are trying solve is only possible using AOP (Aspect Oriented Programming) frameworks. You can modify your loop statement to create a new Integer that has the decremented value or use the AtomicInteger class and its getAndDecrement method. Synt Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company Currently I have list of object array from that array i have to Iterate and add to the list of my LatestNewsDTO what i have done below code working but still i am not satisfy with my way . List; public class TestA { public static void main(String[] args) { List<String> list = new In this article, we demonstrated the different ways to iterate over the elements of a list using the Java API. identity() )); This is just an example for the purposes of posting here. Nothing wrong with using a loop. How to Iterate List in Java. If you have an Iterable, then with Java 8 you can use this solution:. How to Modify 7447 IC Output to Improve 6 and 9 Display on a 7-Segment I have a list of objects and want to iterate in forwards and backwards, until an element is found that is "valid". . Enhanced for Loop. In that case, you need to I am working on a project to try and teach myself spring and struts. Java 8 how to iterate over a nested list of objects. //Tests if this enumeration contains more elements. The only way to iterate over files in a directory seems to be File. : No, because then it wouldn't be a List<T> anymore but a IEnumerable<T> which doesn't support the List. That's about as efficient as it'll get. setValue() method to modify the current entry's value. There's no magic that avoids iterating. 2. Update Here is what I did to keep the things in simplest possible way - to loop through all rows and columns : import java. Java Streams for looping twice over same list. getDeclaredFields(); Or change your current design to have a List<BigDecimal> prices instead of having 6 fields of the same type. How to loop through a custom list? 0. 0. List; import java. If you return an instance of this class, then the remove() method of the returned iterator is disabled. You need to implement Iterable<Customer> in your queue, as shown below, so that your queue can be iterated the same as arrays and other Java collections. map() 3. I have a pojo class with variables eid and ename with getters/setters, I also have a table in sql with the same values with six populated rows. io. tobias_k's answer uses an iterator to get the next combination by iterating over the indices of the lists. I have a Map<Integer,String>. The cost in time and memory isn't too large if you remove them from the old Map as you add to the new one. As it says on MSDN:. Then I modify list to the [1, 2, 3, 4, 5]. Iterator; import java. 7181. Ask Question Asked 4 years, 1 month ago. singleton("test")); List<Foo> fooListCopy = new ArrayList<Foo>(fooList); for(Foo foo : fooListCopy){ // modify actual fooList } and. identity())); An iterator for lists that allows the programmer to traverse the list in either direction, modify the list during iteration, and obtain the iterator's current position in the list. Personally, I would iterate through each Map. The new element is inserted before the implicit cursor: a subsequent call to previous() would return the new element If you just want to remove the element from the collection, you can use Iterator instead of Iterable. iterator() under the hood. java; lambda; If adding a lot of reference objects is acceptable from a performance perspective (indirection and more gc-pressure) and you have control over the dictionary then creating a box for your values would solve the problem, e. Example: {". The ArrayList and LinkedList are widely used in Java. but a possible iteration and adittion of element might look like this. Porting nested for loop over the same list to a Java Stream. Iterator<String> crunchifyIterator = crunchifyList. What we know is every year's events will start with 'Session Start' event. In this blog, we’ll explore 7 different ways to 1. Find the method to obtain instance of ListIterator. Let’s dive into the basics of using a for loop, an enhanced for loop, and an iterator to efficiently navigate through the elements of a list. You can achieve your task by creating a copy is because the keys will remain same in both. setName(f. Class extension exists so we may re-use code. Modifying an Array list while I am iterating over it. In this blog, we’ll explore 7 different ways to iterate over a list in Java, discussing when and why Discover the basics and advanced techniques for iterating a list in Java using for loops, iterators, streams, and learn how to avoid common mistakes like modifying the list The iterator() method of java. Nope, you're good. names (); for (int i = 0; i < keys. I am not familiar with stringPropertyNames but if it is a Map you should be able to do something like (untested code):. My Customer class has 2 data members: Name and Email. Java 8 Iterate List inside an list and stream. An iterator is especially useful when you need to modify the list that is being iterated on. Now iterate on 1 and modify second map. toMap(Emp::getId, Function. Otherwise, what you can do is not to iterate the original collection, but first make a copy of the list. 142. remove() method to remove the current entry, or; use the Map. Is their any efficient way please let me know. What might help more, depending on the size of the lists, might be to convert dateList to a set and then iterate over the slots and checking whether a slot's date is contained in that date set. is there a better solution? Well, there is, definitely, a better way to do so in a single statement, but that depends on the condition based on which elements are removed. Use a variable to store the index in the list "ITERATOR". If it happens to be several times, consider using a Map as suggested by Raz. Java for loop with an ArrayList. hasNext()) { System. iterator(); while (crunchifyIterator. – nwinkler. Key Points: List: An ordered collection that allows duplicate elements. Even when the first element match, you will iterate over all other elements. Hot Network Questions Can an intelligent agent with aims desire to modify itself to change those aims? Poincaré and the principle of induction Orly airport Metro ticket information I have a List<SomeBean> that is populated from a Web Service. It works fine for the usual for loop (int i = 0; i < anArray. List; public class Foo { public static class Card { int val; public Card(int val) { this. to check if type is same as other type like List simply use. Transform the list into a Map using ID as key and having a list of elements. Changing the key value is going to require creating a new Map and either copying the unchanging values or modifying and inserting the changing ones. My program has 4 Computer objects with different values, from Make, Model, Productnumber, Amount, and Shelfnumber. listIterator(myList. asIterator(); java. next(); iter. I can iterate through that deck list using the iterator I have shown but now I want to know how I can modify the iterator to iterate through the Above modify method does work and it does update after I do some Transforming and all, but it is updating all the transactions with same id,time,date values. e Y,Z,A values are, from empty("") strings to some integer values. next()); } // ListIterator - traverse a list of elements in either forward or backward order // An iterator for lists that allows the programmer to traverse the list in either direction, modify the list during iteration, // and obtain I have a number of Customer objects stored in an ArrayList. MyClass { private boolean valid; public boolean isValid() { return valid; } } List<MyClass> classes; //assume sorted list An iterator for lists that allows the programmer to traverse the list in either direction, modify the list during iteration, and obtain the iterator's current position in the list. First, we will understand what happens Fortunately, Java provides a variety of ways to loop through a list, from classic loops to more modern and functional approaches. 14, 2. The point is that there may be some operation that I need to perform on a property. I know that I . Now if "Doe" is located at index 3 in the list, I know I can write this line: myList. Suitable when you want a clean, readable code for iterating over collections. toMap( MyObject::getId Function. I am searching for an efficient way to iterate over thousands of files in one or more directories. I found 5 main ways to iterate over a Linked List in Java (including the Java 8 way): For Loop; Enhanced For Loop; While Loop; Iterator; Collections’s stream() util (Java8) Although you are expecting both sizes to be same, just to be on safer side get the sizes for both of them and make sure they are equal. size()); while (listIter. Let that size value be count. For example if your collection is a list, than you can make a First of all, Set assumes that its elements are immutable (actually, mutable elements are permitted, but they must adhere to a very specific contract, which I doubt your class does). For instance, ["apple", "orange"] to ["iapple", "iorange"]. From the javadoc for add():. You will always iterate over the whole list and calculate the lambda for each element in the list. listIterator; iter. Asking for help, clarification, or responding to other answers. length; i++), but I havn't used this foreach before? Java iterate a list and add to object containing a list. I tried running the code below but the values are not changing. Iterator; import org. To invert the array, you'd want to use a regular for loop: I need to iterate over a collection of items & sometimes add to that collection at the same time. This may be more or less efficient than using a ListIterator (which the default implementation does) depending on the type of list that you are using and how many elements you need to replace since it can be overridden to provide better performance but you can't short circuit it and quit Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company List iterators can be used to iterate your list backwards, too -- like this: ListIterator<String> listIter = myList. Why does the foreach keep giving me an out of bounds exception. The normal objections to extending a class is the "favor composition over inheritance" discussion. – Lee Meador When working with Maps, you have two options for updates like this, iterate through each Map. And then you can use iterator. g. Example: Input: float_list = [3. Add How to stream 2 Lists & modify I'd doubt using streams etc. Java - adding elements to list while iterating over it. 0 and I'm trying to iterate through Java's implementation of a linked list and modify each element of the linked list in constant time. The update clause is used to modify the current state of the index variable, increasing it or decreasing it until the point of termination. a stream iterating over the indices like. @TagirValeev - That is true - but this answer applies to the question title Iterating over two lists using Java 8 streams. Field[] fields = LargeDTO. So when you execute this line: Integer x = i. How to add element in List while iterating in java? 26. Add a comment | Java Iterate Over for(int i=0;i<list. Improve this question. I have a pojo with the list. 1. stream() . Now, I can't seem to get to the part located in the for loop. To concurrently iterate and modify a collection in Java, you must use the "ListIterator" object, and use the iterator's own "add()" and "remove()" methods, and not use the ones on the collection. The . The code would be: This version works with every Java version that supports generic (i. size();i++) { HashMap hMap=new HashMap(); hMap. – OldCurmudgeon. But can I modify an item in a list I'm iterating over if I do not change the list length? You're not modifying the list in any way at all. enumeration(map. Here's an example of taking a List<String>, and constructing a map from a letter to a string starting from that letter from the list. I want to iterate through both collections at the same time and fetch the name and age of each person and do something with it. I am a bit confused though, normally one gets the keys of a map by the keySet method. These functions effectively load the entire list of files in some sort of How to loop across a growing java List. 3. I have a list: val someList = listOf(1, 20, 10, 55, 30, 22, 11, 0, 99) And I want to iterate it while modifying some of the values. However, when you execute: Here is a way to disable the ability of an iterator to change the collection. In this example, we see that it provides a list of all events that happen for a school every year and the list is a cumulative one i. values(). List; public class ReverseIterator<T> implements Iterator<T>, Iterable<T> { private final List<T> list I tried to make a copy of the list . In short, to do modification on the list while iterating the same list. Trying to update nested ArrayList within a You can't modify a Collection while iterating over it using an Iterator, except for Iterator. Basically, iterating over the list with 3 conditions if any of them is satisfied want to break loop and in every condition want to call different method. @pvg Yeah, I could edit my question. Then use generic for loop, iterate till count and acess the values as array indexes. 0, used to iterate over the elements of the legacy collection classes. In need of iterating and modifying arraylist (or similar) at the same time. This is how my file looks like: { &quot;JObjects&quot;: { &quot;JAr This is a simple snippet that shows how to loop through the getters of a certain object to check if the returned values are null, using reflection: import java. Set: An unordered collection that does not allow duplicate elements. Mono<List< Rule>> to Mono<List< RuleResult>> I have this, which works but blocking the execution seems not correct to me: List<Rule> RuleSet It means you can skip elements, iterate backward, or even change multiple elements in one iteration if necessary. Java 8's stream() interface provides a great way to update a list in place. boolean hasMoreElements(); //Returns the next LinkedList<String> list; Iterator iter=list. FileInputStream; import java. Arrays; import java. How can I to fix a nested for? 1. It means you cannot access and modify your collection (List) at the same time. The implementation classes of List interface are ArrayList, LinkedList, Stack, and Vector. I want to add those conversations that its last The iterator you are using is fail-fast iterator. toList()); To safely remove items in place, use In this article, we will discuss and learn with different illustrations on how to add/remove an element to List/ArrayList while iterating. Ask Question Asked 8 years, 1 month ago. The foreach statement is used to iterate through the collection to get the information that you want, but can not be used to add or remove items from the source collection to avoid unpredictable side effects. I think I am making a mistake by calling GetElementsByTagName() method. Fill list with another object list. getKey(); var value = entry. The java. The two basic operations that a Set supports are the addition and removal of elements. 8. In this section, we will learn how to iterate a List in Java. We are given a list of floats and our task is to iterate the list of floats and print the result. Stream API modify list while processing. , not creating Use Class#getDeclaredFields. how to fix iterating through this arraylist? Hot Network Questions As a solo developer, how best to avoid underestimating the difficulty of my game due to knowledge/experience of it? How would 0 visibility I know you should not add/remove items while iterating over a list. There are methods on Map to do both of these things. As an example consider the following figure which shows a couple of single lists and a list of lists (nested lists): From this figure, you can notice that each If you wanna modify current list, use Collection. xml",". Using streams Java 8 to modify in List Java. In this article, we will learn to iterate list in our Java application. There are many ways to iterate list. 718, 1. map(x -> "D"). Editing this answer to work for List<List<T>>. The is a classic However, if the object is immutable (you can't change the contents of the object itself), you don't have the option to modify what's inside the object in the list. class. stream(iterable. skaffman. To avoid the quadratic time complexity, do a pre-processing by constructing a Map<Integer, Emp>. getString (i); // Here's I have a list of Rules that return Mono<Result>, I need to execute them and return another List of Mono with the result of each function. This is very much by design. next(); Over and over again and after many moves of the iterator, I need to "reset" the position of the iterator. As mentioned, there is no defined behavior when the underlying Collection is modified, as noted in the documentation for Iterator. And don't worry about "improving" existing working code using Java 8 features. Java, list of objects, change values in a loop. So, first I want to get the Keys, which works: Set<String> keys = theMap. Now I want to modify just the Email for Customer "Doe". Commented Mar 16, 2012 at 17:39. Iterate and filter a list using Java streams instead of for-each loop. toList()); In Java, can you modify a List while iterating through it? 1. ForEach method. 12. Map: A collection that maps keys to values, with no duplicate keys allowed. Iterate through 2 lists at the same time. However, if you use the listIterator() method, which returns a ListIterator, and iterate over that you have more options to modify. map. hasNext()){ // modify actual fooList using itr. hasNext() like // you would do in a while-loop. eojeg wwiy ekait hzbtf dfbu iduqsx whf ybgptmm ednjvf nzfqi