ArrayList in Java

by

ArrayList is one of the most used Collections in java. It is a dynamic array which means its size can increase automatically as more elements are added to it. Let us see how to create an arraylist:

ArrayList<Integer> arrList = new ArrayList<Integer>();

We need to give the object type within angle brackets which tells the type of elements stored in the arraylist.

Important points about ArrayList :-

  • As elements are added the size of ArrayList also increases.
  • ArrayList is present in java.util package.
  • It implements List interface.
  • We can also specify the initial size of the ArrayList while calling its constructor.
  • Multiple null values can be inserted in arraylist.
  • The order in which values are inserted in arraylist is maintained.

Let us look at an example code:

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class Tech4Humans {

	public static void main(String[] args) {
		
		// ArrayList initialization without specifying the initial size
		ArrayList<Integer> arrList1 = new ArrayList<Integer>();
		arrList1.add(20);
		arrList1.add(30);	
		System.out.println("arrayList1 = "+arrList1);
		
		
		// ArrayList initialization without specifying the initial size
		ArrayList<Integer> arrList2 = new ArrayList<Integer>(3);
		arrList2.add(20);
		arrList2.add(30);	
		arrList2.add(40);	
		arrList2.add(50);
		arrList2.add(60);	
		System.out.println("arrayList2 = "+arrList2);
		
		
		// ArrayList object assigned to List type reference variable
		List<String> arrList3 = new ArrayList<String>();
		arrList3.add("hello");
		arrList3.add("world");	
		System.out.println("arrayList3 = "+arrList3);
		
		
		// for loop to print the arrayList
		System.out.print("\nArraylist print using for loop = ");
		for(int i=0; i<arrList2.size(); i++) {
			System.out.print(arrList2.get(i)+" ");
		}
		
		
		// for each loop to print the arrayList
		System.out.print("\nArraylist print using for each loop = ");
		for(Integer temp:arrList2) {
			System.out.print(temp+" ");
		}
		
		
		// using Iterator to print arrayList
		System.out.print("\nArraylist print using iterator = ");
		Iterator<Integer> iter = arrList2.iterator();
		while(iter.hasNext()) {
			System.out.print(iter.next()+" ");
		}
	}

}

Output

arrayList1 = [20, 30]
arrayList2 = [20, 30, 40, 50, 60]
arrayList3 = [hello, world]

Arraylist print using for loop = 20 30 40 50 60 
Arraylist print using for each loop = 20 30 40 50 60 
Arraylist print using iterator = 20 30 40 50 60

Let us see what is the default size of ArrayList when it is created.

Leave a Comment