How to Find length/size of an ArrayList in Java with Example

To find the length or size of ArrayList in java one can use java.util.ArrayList size() method.

According to ArrayList Oracle docs, size() method returns the number of elements present in the ArrayList.

ArrayList size() method is different from capacity of ArrayList. Each object of the ArrayList has a capacity. The capacity is the size of the array used to store the elements in the list. Capacity will always atleast as large as the size of the list. As we know ArrayList is dynamic in nature. The capacity of the ArrayList grows automatically, as elements are added to it. When you do not specify capacity while creating the object of ArrayList ,then the object is created with default capacity 10.

I have shared two examples of finding length/size of ArrayList
1. Integer ArrayList object
2. String ArrayList  object

Read Also :   How to sort an ArrayList in Java with Example

ArrayList size() example in Java 

When you create an Object of an ArrayList, it is created as empty ArrayList  and it's size() will be zero.If you add elements one by one then size grows one by one.

1. Java Program to find Length/Size of Integer ArrayList

import java.util.*;
import java.io.*;

/* Write a program to determine the size/length of the ArrayList*/
public class ArrayListSize
{
    public static void main (String[] args)
    { 

        // Create an Integer ArrayList Object

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

        // Print initial size of ArrayList  

        System.out.println("Size before adding elements: "+arrlist.size()); 

        // Adding elements to ArrayList Object

        arrlist.add(11);
        arrlist.add(3);
        arrlist.add(5);
        arrlist.add(4);
        arrlist.add(9);

        /* Print size of ArrayList

           after adding elements */ 
        System.out.println("Size after adding elements: "+arrlist.size()); 

        // Removing elements from ArrayList 

        arrlist.remove(1);
        arrlist.remove(2);

        /* Print size of ArrayList 

           after removing elements */ 
        System.out.println("Size after removing elements: "+arrlist.size()); 

        // Print ArrayList

        System.out.println("Resulting ArrayList: ");
        for(int num: arrlist){
            System.out.println(num);
        }
    }
}

Output :

Size before adding elements: 0
Size after adding elements: 5
Size after removing elements: 3
Resulting ArrayList: 
11
5
9

2. Java Program to find Length/Size of String ArrayList

import java.util.*;
import java.io.*;

/* Program to find size of ArrayList in Java */
public class ArrayListSize
{
        public static void main (String[] args) 
   {
       System.out.println("Java Program to find the size of ArrayList"); 

       // Create an String ArrayList Object 

       ArrayList<String> listOfCities = new ArrayList<>(); 

       int size = listOfCities.size(); 

       // Print initial size of ArrayList   

       System.out.println("size of ArrayList after creation: " + size);

       // Adding elements to ArrayList Object 
       listOfCities.add("California");
       listOfCities.add("Boston");
       listOfCities.add("New York"); 

       size = listOfCities.size(); 

       /* Print size of ArrayList 

          after adding elements */  

       System.out.println("size of ArrayList after adding elements: " + size); 

       // clear() method removes all elements

       listOfCities.clear(); 

       size = listOfCities.size();
       System.out.println("size of ArrayList after clearing elements: " + size);
   }
}

Output :

Java Program to find the size of ArrayList
size of ArrayList after creation: 0
size of ArrayList after adding elements: 3
size of ArrayList after clearing elements: 0