Iterating over ArrayLists in Java
Prerequisite : ArrayList in Java
Method 1 : Using for loop :
// Java program to iterate over an ArrayList// using for loopimport java.util.*;class GFG { public static void main(String[] args) { // initializing ArrayList List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8); // For Loop for iterating ArrayList for (int i = 0; i < numbers.size(); i++) System.out.print(numbers.get(i) + " "); }} |
Output:
1 2 3 4 5 6 7 8
Method 2: Using for each loop
// Java program to iterate// over an arraylist using for Each loopimport java.util.*;class GFG { public static void main(String[] args) { // initializing ArrayList List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8); // For Each Loop for iterating ArrayList for (Integer i : numbers) System.out.print(i + " "); }} |
Output:
1 2 3 4 5 6 7 8
Method 3 : Using Iterator
// Java program to iterate over an arraylist// using Iteratorimport java.util.*;class GFG { public static void main(String[] args) { // initializing ArrayList List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8); // Looping ArrayList using Iterator Iterator it = numbers.iterator(); while (it.hasNext()) System.out.print(it.next() + " "); }} |
Output:
1 2 3 4 5 6 7 8
Method 3 : Using For Each Method of Java 8
// Java program to iterate over an arraylist// using Iteratorimport java.util.*;class GFG { public static void main(String[] args) { // initializing ArrayList List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8); //lambda numbers.forEach(number->System.out.println(number)); }} |
Output:
1 2 3 4 5 6 7 8
Removing Items during Traversal :
It is not recommended to use ArrayList.remove() when iterating over elements. This may lead to ConcurrentModificationException (Refer this for a sample program with this exception). When iterating over elements, it is recommended to use Iterator.remove() method .
// Java program to demonstrate working of// Iterator.remove() on an integer arraylistimport java.util.List;import java.util.ArrayList;import java.util.Iterator; public class GFG{ public static void main(String[] args) { List<Integer> al = new ArrayList<Integer>(); al.add(10); al.add(20); al.add(30); al.add(1); al.add(2); // Remove elements smaller than 10 using // Iterator.remove() Iterator itr = al.iterator(); while (itr.hasNext()) { int x = (Integer)itr.next(); if (x < 10) itr.remove(); } System.out.println("Modified ArrayList : " + al); }} |
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