Stream mapWithIndex Method Provided by the Java Guava Library

This page explains the mapWithIndex method in the Guava library.
Tags:

Providing an index in Stream map

The map function available in Java Stream cannot receive an index.

Starting with version 21, guava provides mapWithIndex, a map for Stream that can receive an index.

Let’s look at it with a simple example.

package com.devkuma.guava.stream;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

import com.google.common.collect.Streams;

public class MapWithIndex {
    public static void main(String[] args) {
        List<String> results = Streams.mapWithIndex(
                Arrays.asList("a", "b", "c").stream(),
                (str, index) -> str + ":" + index
        ).collect(Collectors.toList());

        results.stream().forEach(r -> {
            System.out.println(r);
        });
    }
}

Execution result:

a:0
b:1
c:2

The first argument specifies the collection or array to turn into a Stream, and the second argument specifies a lambda expression.