Apply a function to each item of a List in Java

This post will discuss how to apply a function to each item of a List in Java.

1. Using `List.replaceAll()` method

The List interface provides the replaceAll() method, which can be used to apply a specified operator to each element of the list.

import java.util.Arrays;

import java.util.List;

class Main

{

public static void main(String[] args)

{

List<String> words = Arrays.asList("a", "b", "c", "d");

words.replaceAll(String::toUpperCase);

System.out.println(words);

}

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Output:

[A, B, C, D]

2. Using `Stream.map()` method

With Java 8 Stream API, you can get a sequential stream over the list and call the map() method to apply a given function to the elements of the stream. This approach can be used when you need a new list, and leave the original list unchanged.

import java.util.Arrays;

import java.util.List;

import java.util.stream.Collectors;

class Main

{

public static void main(String[] args)

{

List<String> words = Arrays.asList("a", "b", "c", "d");

List<String> caps = words.stream().map(String::toUpperCase)

.collect(Collectors.toList());

System.out.println(caps);

}

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Output:

[A, B, C, D]

This is equivalent to:

import java.util.ArrayList;

import java.util.Arrays;

import java.util.List;

class Main

{

public static void main(String[] args)

{

List<String> words = Arrays.asList("a", "b", "c", "d");

List<String> caps = new ArrayList<>();

for (String word : words) {

caps.add(word.toUpperCase());

}

System.out.println(caps);

}

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Output:

[A, B, C, D]

3. Using Guava

If you use the Guava library in your project, you may want to use the Lists.transform() method. It returns a new list after applying a specified function to each element of the original list.

import com.google.common.collect.Lists;

import java.util.Arrays;

import java.util.List;

class Main

{

public static void main(String[] args)

{

List<String> words = Arrays.asList("a", "b", "c", "d");

List<String> caps = Lists.transform(words, word -> word.toUpperCase());

System.out.println(caps);

}

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Output:

[A, B, C, D]

That’s all about applying a function to each item of a List in Java.

Apply a function to each item of a List in Java

1. Using List.replaceAll() method

2. Using Stream.map() method

3. Using Guava

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1. Using `List.replaceAll()` method

2. Using `Stream.map()` method