Java 25 (LTS) reference · Stream API

Java Stream mapToInt() Method

Map to an IntStream of primitive ints, which has sum(), average(), min(), max() and summaryStatistics().

Java 25 (LTS) Since Java 8

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Syntax

stream.mapToInt(mapper)

Parameters

Parameter	Description
`mapper` ToIntFunction<T>	Function returning an `int`.

Return value

An IntStream.

Examples

Sum and max of lengths

import java.util.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) {
        List<String> words = List.of("java", "streams", "api");
        System.out.println(words.stream().mapToInt(String::length).sum());
        System.out.println(words.stream().mapToInt(String::length).max().getAsInt());
    }
}

Output

14
7

Run this on your computer — see “Get Started” for setup.

Statistics and ranges

import java.util.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) {
        IntSummaryStatistics stats = Stream.of(70, 85, 92).mapToInt(Integer::intValue).summaryStatistics();
        System.out.println(stats.getMin() + " " + stats.getMax() + " " + stats.getAverage());
        System.out.println(IntStream.rangeClosed(1, 5).sum());
    }
}