ArrayList isEmpty() method - Syntax and Examples

Java ArrayList isEmpty() method - Syntax and Examples

This reference explains ArrayList isEmpty() method - Syntax and Examples through its syntax, examples and boundaries. Use the linked course lessons when the surrounding Java concepts are unfamiliar.

The isEmpty() method in Java's ArrayList class is a straightforward way to check if an ArrayList contains any elements. It returns true if the list is empty (contains zero elements), and false otherwise. It’s often used as a preliminary check before attempting operations that might fail on an empty list, like trying to access its first element or iterate over it.

public boolean isEmpty()

This example demonstrates how to use isEmpty() with a newly created, empty ArrayList.

import java.util.ArrayList;

public class IsEmptyExample {
    public static void main(String[] args) {
        // Create an empty ArrayList
        ArrayList names = new ArrayList<>();

        // Check if the list is empty
        boolean isEmpty = names.isEmpty();

        // Print the result
        System.out.println("Is the ArrayList empty? " + isEmpty);
    }
}

Is the ArrayList empty? true

Here, we create an ArrayList called names. Since it's just created, it has no elements, so isEmpty() returns true.

This example shows how isEmpty() behaves when the ArrayList contains elements.

import java.util.ArrayList;

public class IsNotEmptyExample {
    public static void main(String[] args) {
        // Create an ArrayList and add some elements
        ArrayList numbers = new ArrayList<>();
        numbers.add(10);
        numbers.add(20);
        numbers.add(30);

        // Check if the list is empty
        boolean isEmpty = numbers.isEmpty();

        // Print the result
        System.out.println("Is the ArrayList empty? " + isEmpty);
    }

Is the ArrayList empty? false

In this case, we add three integers to the numbers list. Because it now contains elements, isEmpty() returns false.

This example demonstrates a common use case: checking if an ArrayList is empty *before* attempting to iterate over it. This prevents potential errors like NullPointerException or unexpected behavior when dealing with empty lists in loops.

import java.util.ArrayList;

public class IsEmptyBeforeIteration {
    public static void main(String[] args) {
        // Create an ArrayList of Strings
        ArrayList fruits = new ArrayList<>();

        // Check if the list is empty before iterating
        if (!fruits.isEmpty()) {
            for (String fruit : fruits) {
                System.out.println(fruit);
            }
        } else {
            System.out.println("The list of fruits is empty.");
        }
    }

The list of fruits is empty.

Because the fruits list is initially empty, the if (!fruits.isEmpty()) condition evaluates to false. The `else` block then executes and prints a message indicating that the list is empty.

This example demonstrates how you can use isEmpty() inside a custom method to perform certain operations based on whether or not an ArrayList is empty. This promotes code reusability and makes your logic clearer.

import java.util.ArrayList;

public class IsEmptyInMethod {
    // Method to print elements only if the list isn't empty
    public static void printElements(ArrayList list) {
        if (!list.isEmpty()) {
            for (String item : list) {
                System.out.println(item);
            }
        } else {
            System.out.println("The list is empty, nothing to print.");
        }
    }

    public static void main(String[] args) {
        ArrayList numbers = new ArrayList<>();
        printElements(numbers);

        ArrayList names = new ArrayList<>();
        names.add("Alice");
        names.add("Bob");
        printElements(names);
    }
}

The list is empty, nothing to print.
Alice
Bob

The printElements method checks if the provided ArrayList is empty before attempting to iterate and print its contents. This keeps your code clean and prevents errors that could occur when working with potentially empty lists.

Check the example’s types, inputs and documented behavior before copying it into an application. Some APIs require external libraries, files or platform services; consult their setup notes.

Related explanations: Java Data Types - Primitive and Non-Primitive, Java Class - Blueprint of Objects, Exceptions in Java Introduction.

Supporting documentation: Official Java learning guide.