ArrayList forEach() Method in Java

The forEach() method of the ArrayList class is used to iterate over each element of an ArrayList and perform a specified action on every element. Introduced in Java 8, it accepts a Consumer functional interface, making it easy to use lambda expressions and method references for concise and readable code.

• Simplifies iteration without using explicit loops.
• Introduced in Java 8 as part of the Collections Framework enhancements.

import java.util.ArrayList;

public class GFG {
    public static void main(String[] args) {

        // Create an ArrayList of Strings
        ArrayList<String> s = new ArrayList<>();
        s.add("Cherry");
        s.add("Blueberry");
        s.add("Strawberry");

        // Use forEach() to print each fruit
        s.forEach(System.out::println);
    }
}

Cherry
Blueberry
Strawberry

Explanation: In the above example, we use the forEach() method with a method reference (System.out::println) to print each element in the ArrayList.

Syntax

public void forEach(Consumer<? super E> action)

Parameter: action: A functional interface "Consumer" that specifies the action to be performed for each element in the ArrayList. It accepts a single parameter and does not return any value.

Exception: This method throws NullPointerException if the specified action is null.

Example: Using the forEach() method with a lambda expression to print the square of each element in an ArrayList of Integers.

import java.util.ArrayList;

public class GFG {
    public static void main(String[] args) {

        // Create an ArrayList of Integers
        ArrayList<Integer> n = new ArrayList<>();
        n.add(2);
        n.add(3);
        n.add(4);

        // Use forEach() to print the 
        // square of each number
        n.forEach(num -> System.out.println(num * num));
    }
}

4
9
16

Explanation: Here, an ArrayList<Integer> is created with the values 2, 3, and 4. The forEach() method uses a lambda expression to calculate and print the square of each number during iteration.

Example: Using the forEach() method with a conditional statement to filter and print eligible elements of an ArrayList of Integers.

import java.util.ArrayList;

public class GFG {
    public static void main(String[] args) {

        // Create an ArrayList of Integers
        ArrayList<Integer> a = new ArrayList<>();
        a.add(24);
        a.add(18);
        a.add(10);

        // Use forEach() to print 
        // ages that are 18 or above
        a.forEach(age -> {
            if (age >= 18) {
                System.out.println("Eligible age: " + age);
            }
        });
    }
}

Eligible age: 24
Eligible age: 18

Explanation: In the above example, we use the forEach() method with a lambda expression and conditional logic to filter and print elements based on a condition.

Difference Between forEach() and Enhanced for Loop

Advantages of forEach() Method

• Makes iteration concise and readable.
• Eliminates the need for explicit loops.
• Supports functional programming with lambda expressions.
• Works seamlessly with method references.
• Reduces boilerplate code.
• Suitable for applying the same operation to every element.