How to remove an element from ArrayList in Java?

07 Jul, 2022
ArrayList is a part of collection framework and is present in java.util package. It provides us with dynamic arrays in Java. Though, it may be slower than standard arrays but can be helpful in programs where lots of manipulation in the array is needed. This class is found in java.util package. With the introduction and upgradations in java versions, newer methods are being available if we do see from Java8 perceptive lambda expressions and streams concepts were not available before it as it was introduced in java version8, so do we have more ways to operate over Arraylist to perform operations. Here we will be discussing a way to remove an element from an ArrayList.
While removing elements from ArrayList there can either we are operating to remove elements over indexes or via values been there in an ArrayList. We will be discussing both ways via interpreting through a clean java program. 
Methods:
There are 3 ways to remove an element from ArrayList as listed which later on will be revealed as follows:
Using remove() method by indexes(default)Using remove() method by valuesUsing remove() method over iterators
Using remove() method by indexes(default)
Using remove() method by values
Using remove() method over iterators
Note: It is not recommended to use ArrayList.remove() when iterating over elements. 
Method 1: Using remove() method by indexes
It is a default method as soon as we do use any method over data structure it is basically operating over indexes only so whenever we do use remove() method we are basically removing elements from indices from an ArrayList.
ArrayList class provides two overloaded remove() methods. 
remove(int index): Accepts the index of the object to be removed
remove(Object obj): Accepts the object to be removed
Let us figure out with the help of examples been provided below as follows:
Example:
Java
// Java program to Remove Elements from ArrayList// Using remove() method by indices  // Importing required classesimport java.util.ArrayList;import java.util.List;  // Main classpublic class GFG {    // Main driver method    public static void main(String[] args)    {        // Creating an object of List interface with        // reference to ArrayList class        List<Integer> al = new ArrayList<>();          // Adding elements to our ArrayList        // using add() method        al.add(10);        al.add(20);        al.add(30);        al.add(1);        al.add(2);          // Printing the current ArrayList        System.out.println(al);          // This makes a call to remove(int) and        // removes element 20        al.remove(1);          // Now element 30 is moved one position back        // So element 30 is removed this time        al.remove(1);          // Printing the updated ArrayList        System.out.println(al);    }}
[10, 20, 30, 1, 2]
[10, 1, 2]
Now we have seen removing elements in an ArrayList via indexes above, now let us see that the passed parameter is considered an index. How to remove elements by value. 
Method 2: Using remove() method by values
Example:
Java
// Java program to Remove Elements from ArrayList// Using remove() method by values  // Importing required classesimport java.util.ArrayList;import java.util.List;  // Main classpublic class GFG {    // Main driver method    public static void main(String[] args)    {        // Creating an object of List interface with        // reference to ArrayList        List<Integer> al = new ArrayList<>();          // Adding elements to ArrayList class        // using add() method        al.add(10);        al.add(20);        al.add(30);        al.add(1);        al.add(2);          // Printing the current ArrayList        System.out.println(al);          // This makes a call to remove(Object) and        // removes element 1          al.remove(Integer.valueOf(1));          // This makes a call to remove(Object) and        // removes element 2        al.remove(Integer.valueOf(2));                  // Printing the modified ArrayList        System.out.println(al);    }}
Output : 
[10, 20, 30,1 ,2]
[10, 20, 30]
Note: It is not recommended to use ArrayList.remove() when iterating over elements. 
Also new Integer( int_value) has been deprecated since Java 9, so it is better idea to use Integer.valueOf(int_value) to convert a primitive integer to Integer Object.
Method 3: Using Iterator.remove() method 
This may lead to ConcurrentModificationException  When iterating over elements, it is recommended to use Iterator.remove() method. 
Example:
Java
// Java program to demonstrate working of// Iterator.remove() on an integer ArrayListimport java.util.ArrayList;import java.util.Iterator;import java.util.List;  public class GFG {      // Main driver method    public static void main(String[] args)    {        // Creating an ArrayList        List<Integer> al = new ArrayList<>();          // Adding elements to our ArrayList        // using add() method        al.add(10);        al.add(20);        al.add(30);        al.add(1);        al.add(2);          // Printing the current ArrayList        System.out.println(al);          // Creating iterator object        Iterator itr = al.iterator();          // Holds true till there is single element        // remaining in the object        while (itr.hasNext()) {              // Remove elements smaller than 10 using            // Iterator.remove()            int x = (Integer)itr.next();            if (x < 10)                itr.remove();        }          // Printing the updated ArrayList        System.out.print(al);    }}
[10, 20, 30, 1, 2]
[10, 20, 30]
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