Java Iterator forEachRemaining() Method

The forEachRemaining() method in Java, part of the java.util.Iterator interface, is used to perform the given action for each remaining element of the iterator until all elements have been processed or the action throws an exception.

Table of Contents

1. Introduction
2. forEachRemaining() Method Syntax
3. Understanding forEachRemaining()
4. Examples
   • Basic Usage
   • Using a Lambda Expression
5. Real-World Use Case
6. Conclusion

Introduction

The forEachRemaining() method allows you to perform a specified action on each remaining element of an iterator. This can be particularly useful when you need to apply a function to all elements without manually iterating through them.

forEachRemaining() Method Syntax

The syntax for the forEachRemaining() method is as follows:

default void forEachRemaining(Consumer<? super E> action)

Parameters:

• action: A Consumer that performs the action on each remaining element.

Returns:

• This method does not return a value.

Throws:

• NullPointerException: If the specified action is null.

Understanding forEachRemaining()

The forEachRemaining() method processes all remaining elements in the iterator using the specified action. The action is a Consumer functional interface, which takes a single input argument and performs an operation without returning any result.

Examples

Basic Usage

To demonstrate the basic usage of forEachRemaining(), we will create a list of integers and use an iterator to apply an action to each remaining element.

Example

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

public class ForEachRemainingExample {
    public static void main(String[] args) {
        List<Integer> numbers = new ArrayList<>();
        numbers.add(1);
        numbers.add(2);
        numbers.add(3);
        numbers.add(4);
        numbers.add(5);

        Iterator<Integer> iterator = numbers.iterator();

        Consumer<Integer> action = new Consumer<Integer>() {
            @Override
            public void accept(Integer number) {
                System.out.println("Number: " + number);
            }
        };

        iterator.forEachRemaining(action);
    }
}

Output:

Number: 1
Number: 2
Number: 3
Number: 4
Number: 5

Using a Lambda Expression

This example shows how to use a lambda expression with the forEachRemaining() method for more concise code.

Example

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

public class ForEachRemainingLambdaExample {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");
        names.add("Diana");

        Iterator<String> iterator = names.iterator();
        iterator.forEachRemaining(name -> System.out.println("Name: " + name));
    }
}

Output:

Name: Alice
Name: Bob
Name: Charlie
Name: Diana

Real-World Use Case

Processing Data Streams

In a real-world scenario, you might use the forEachRemaining() method to process elements in a data stream, such as applying a function to each element in a collection without writing explicit iteration logic.

Example

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

public class DataProcessingExample {
    public static void main(String[] args) {
        List<Double> prices = new ArrayList<>();
        prices.add(19.99);
        prices.add(29.99);
        prices.add(39.99);
        prices.add(49.99);

        Iterator<Double> iterator = prices.iterator();
        iterator.forEachRemaining(price -> System.out.println("Price with tax: " + (price * 1.2)));
    }
}

Output:

Price with tax: 23.987999999999996
Price with tax: 35.988
Price with tax: 47.988
Price with tax: 59.988

Conclusion

The Iterator.forEachRemaining() method in Java provides a way to perform a specified action on each remaining element of an iterator. By using this method, you can streamline the process of applying functions to all elements in a collection, making it particularly useful for data processing and other iterative operations. 

Whether you use a traditional Consumer implementation or a lambda expression, the forEachRemaining() method offers a flexible and efficient way to handle remaining elements in an iterator.