Java Arraylist Remove() In Addition To Removeall() - Representative Tutorial

In this Java ArrayList tutorial, you lot volition larn how to take away elements from ArrayList inwards Java e.g. you lot tin give the axe take away String from ArrayList of String or Integer from ArrayList of Integers. There are genuinely 2 methods to take away an existing chemical ingredient from ArrayList, starting fourth dimension past times using the remove(int index) method, which removes elements amongst given index, recollect index starts amongst null inwards ArrayList. So a telephone telephone to remove(2) inwards an ArrayList of {"one", "two", "three"} volition take away tertiary chemical ingredient which is "three". The 2d method to take away chemical ingredient is remove(Object obj), which removes given object from ArrayList. For example, a telephone telephone to remove("two") volition take away the 2d chemical ingredient from ArrayList. Though you lot should recollect to role Iterator or ListIterator remove() method to delete elements piece iterating, using ArrayList's take away methods, inwards that case, volition throw ConcurrentModificationException inwards Java.

Things acquire piddling complicated when you lot are working amongst ArrayList of integral numbers e.g. ArrayList of integers. If your listing contains numbers which are same every bit indexes e.g. thence a telephone telephone to remove(int index) tin give the axe live on confused amongst a telephone telephone to remove(Object obj).

For example, if you lot own got an ArrayList containing {1, 2, 3} thence a telephone telephone to remove(2) is ambiguous, because it could live on interpreted a telephone telephone to take away 2, which is 2d chemical ingredient or a telephone telephone to take away chemical ingredient at index 2, which is genuinely 3.

If you lot desire to larn to a greater extent than well-nigh Collection classes, I advise you lot to accept a expect at 1 of the all fourth dimension classic book, Java Generics as well as Collection. This is the volume I refer to refresh my noesis on the topic.

Java ArrayList Remove Object Example

Here is the Java plan to take away a given object from ArrayList inwards Java. In this example, I own got used the 2d take away method, which deletes the given object from ArrayList. Anyway, since nosotros own got an ArrayList of String, you lot tin give the axe role whatever of those method, its safe. You tin give the axe too banking firm fit size() of ArrayList earlier as well as afterwards removing elements.

Remember, size() method gives full set out of elements inwards ArrayList, thence it should trim back past times one. This is unlike than the size of array which is backing ArrayList, which volition rest same. In our example, you lot tin give the axe meet that set out of elements are gradually reduced afterwards removal.

By using index you lot tin give the axe easily take away starting fourth dimension or concluding chemical ingredient from ArrayList inwards Java. Since index starts at null inwards ArrayList, you lot tin give the axe take away starting fourth dimension chemical ingredient past times passing null to take away method e.g. remove(0) as well as to take away concluding chemical ingredient from ArrayList, you lot tin give the axe locomote past times size - 1 to remove(int index) method e.g. remove(arraylist.size() - 1) volition take away the concluding chemical ingredient from ArrayList. Remember, unlinke array, at that spot is no length mehtod inwards ArrayList, thence you lot ask to role the size() method which returns full set out of elements inwards the ArrayList.


Time complexity of remove(int index) method is O(n) because it's non but delete the chemical ingredient at specified index but too shifts whatever subsequent elements to the left i.e. substracts 1 from their indices. For example, if arraylist has 10 elements as well as you lot removed fourth chemical ingredient i.e. index 3 thence all chemical ingredient starting from fifth to tenth volition shift lower e.g. fifth volition come upward to 4th, sixth volition come upward to fifth as well as thence on.

There is 1 to a greater extent than method removeAll(Collection c) which you lot tin give the axe role to take away all elements specified inwards the given collection. This method provide truthful if ArrayList chaned past times calling this method i.e. 1 to a greater extent than elements are removed. You tin give the axe role this method to take away elements inwards mass from ArrayList. This method volition throw ClassCastException if cast of the chemical ingredient of this listing is non compatible amongst the cast of the chemical ingredient inwards the given collection. It volition too throw NullPointerException if this listing contains a goose egg chemical ingredient as well as specified collection doesn't permit goose egg elements or specified collection itself is null.

Though, you lot shouldn't role these methods when you lot are removing elements piece iterating over ArrayList. In that instance you lot must role Iterator's remove() method to avoid ConcurrentModificationException. You tin give the axe farther read Core Java Volume 1 - Fundamentals past times Cay S. Horstmann to larn to a greater extent than well-nigh how to take away objects from ArrayList inwards Java. One of the most comprehensive even thence tardily to read volume on Java programming.

Java Program to take away String from ArrayList

import java.util.ArrayList;  /**  * Java plan to take away an chemical ingredient from ArrayList  *  * @author WINDOWS 8  */  public class ArrayListRemoveDemo{      public static void main(String args[]) {          ArrayList<String> cities = new ArrayList<>();         cities.add("London");         cities.add("Tokyo");         cities.add("HongKong");         cities.add("NewYork");         cities.add("Berlin");                         System.out.println("Before removing whatever chemical ingredient from ArrayList : " + cities);         cities.remove("London");                 System.out.println("After removing 1 chemical ingredient from ArrayList : " + cities);         cities.remove("Tokyo");                 System.out.println("After removing 2 objects from ArrayList : " + cities);            }  }  Output Before removing whatever chemical ingredient from ArrayList : [London, Tokyo, HongKong, NewYork, Berlin] After removing 1 chemical ingredient from ArrayList : [Tokyo, HongKong, NewYork, Berlin] After removing 2 objects from ArrayList : [HongKong, NewYork, Berlin]

Here is roughly other Java instance to take away an object at given index cast ArrayList  in Java.

overloading best practices.

Further Learning
Java In-Depth: Become a Complete Java Engineer
Java Fundamentals: Collections
Data Structures as well as Algorithms: Deep Dive Using Java
Algorithms as well as Data Structures - Part 1 as well as 2
Data Structures inwards Java ix past times Heinz Kabutz