Pass ArrayList as Function Argument in Java

The ArrayList is a resizable array, which is part of java.util package. The difference between a built-in array and an ArrayList in Java is that the size of an array cannot be modified.

In this article, we will understand how to pass an ArrayList as a function argument.

Following are the ways to pass an ArrayList as a function argument:

• Using Function Argument
• Using Return Type

Using Function Argument

We can pass an ArrayList as a function argument in Java. The function can take an ArrayList as a parameter and perform operations on it.

Example

In the following example, we will create an ArrayList of integers and then pass it as a function argument to calculate the sum of its elements.

import java.util.ArrayList;
import java.util.List;
public class ArrayListFunctionArgument {
   public static void main(String[] args){
      List<Integer> numbers = new ArrayList<>();
      numbers.add(1);
      numbers.add(2);
      numbers.add(3);
      numbers.add(4);
      System.out.println("Numbers List: " + numbers);
      int sum = calculateSum(numbers);
      System.out.println("Sum of elements: " + sum);
   }
    public static int calculateSum(List<Integer> list) {
        int sum = 0;
        for (int number : list) {
            sum += number;
        }
        return sum;
    }
}

Following is the output of the above code:

Numbers List: [1, 2, 3, 4]
Sum of elements: 10

Using Return Type

We will create a function that returns an ArrayList. The function can perform operations on the ArrayList and return it.

Example

In the following example, we will create a function that returns an ArrayList of integers. We will then call this function and print the returned ArrayList.

import java.util.ArrayList;
import java.util.List;
public class ArrayListReturnType {
   public static void main(String[] args) {
      List<Integer> numbers = getNumbers();
      System.out.println("Returned Numbers List: " + numbers);
   }
   
   public static List<Integer> getNumbers() {
      List<Integer> list = new ArrayList<>();
      list.add(5);
      list.add(10);
      list.add(15);
      return list;
   }
}

Following is the output of the above code:

Returned Numbers List: [5, 10, 15]