Java IntConsumer Interface

Last modified: April 16, 2025

The java.util.function.IntConsumer interface represents an operation that accepts a single int-valued argument and returns no result. It is a functional interface with a single abstract method accept.

IntConsumer is part of Java’s functional programming utilities added in Java 8. It is the primitive specialization of Consumer for int. This avoids autoboxing overhead when working with primitive int values.

IntConsumer Interface Overview

IntConsumer interface contains one abstract method and one default method. The key method accept performs the operation on the input. The andThen method enables chaining of consumers.

@FunctionalInterface public interface IntConsumer { void accept(int value);

default IntConsumer andThen(IntConsumer after);

}

The code above shows the structure of IntConsumer interface. It is annotated with @FunctionalInterface to indicate its single abstract method nature. The interface is designed for side-effect operations on int values.

Basic IntConsumer Usage

The simplest way to use IntConsumer is with lambda expressions. We define what to do with the input int value in the accept method. The example prints numbers.

Main.java

package com.zetcode;

import java.util.function.IntConsumer;

public class Main {

public static void main(String[] args) {

    // Define a consumer that prints the number
    IntConsumer printNumber = n -> System.out.println("Number: " + n);
    
    // Use the consumer
    printNumber.accept(5);
    printNumber.accept(10);
    
    // Consumer that squares the number and prints
    IntConsumer squareAndPrint = n -> System.out.println(n + " squared: " + n * n);
    squareAndPrint.accept(4);
}

}

This example demonstrates basic IntConsumer usage with lambda expressions. The printNumber consumer simply prints the input value. The squareAndPrint consumer performs a calculation before printing. Consumers are useful for side effects.

Chaining Consumers with andThen

The andThen method allows chaining consumers where each consumer processes the same input value in sequence. This enables modular side effects.

Main.java

package com.zetcode;

import java.util.function.IntConsumer;

public class Main {

public static void main(String[] args) {

    // First consumer prints the number
    IntConsumer print = n -> System.out.println("Original: " + n);
    
    // Second consumer prints the number doubled
    IntConsumer printDouble = n -> System.out.println("Doubled: " + n * 2);
    
    // Chain the consumers
    IntConsumer combined = print.andThen(printDouble);
    
    // Execute the chain
    combined.accept(7);
    combined.accept(12);
}

}

This example shows consumer chaining with andThen. The same input value (7 and 12) flows through both consumers. Each consumer performs its operation independently. The order of execution is guaranteed.

IntConsumer with Streams

IntConsumer is commonly used with IntStream for processing primitive int values. The forEach method accepts an IntConsumer to process each element.

Main.java

package com.zetcode;

import java.util.stream.IntStream;

public class Main {

public static void main(String[] args) {

    // Create a range of numbers
    IntStream numbers = IntStream.rangeClosed(1, 5);
    
    // Define a consumer that processes each number
    numbers.forEach(n -> {
        System.out.println("Processing: " + n);
        System.out.println("Square root: " + Math.sqrt(n));
    });
    
    // Another example with method reference
    IntStream.of(10, 20, 30).forEach(System.out::println);
}

}

This example demonstrates IntConsumer usage with IntStream. The lambda passed to forEach is an IntConsumer that processes each stream element. Method references can also be used when the operation matches an existing method.

Stateful IntConsumer

While generally discouraged, IntConsumers can maintain state. This example shows a consumer that tracks and reports statistics about the numbers it processes.

Main.java

package com.zetcode;

import java.util.function.IntConsumer;

public class Main {

public static void main(String[] args) {

    // Stateful consumer that tracks statistics
    class StatsConsumer implements IntConsumer {
        private int count = 0;
        private int sum = 0;
        private int min = Integer.MAX_VALUE;
        private int max = Integer.MIN_VALUE;
        
        @Override
        public void accept(int value) {
            count++;
            sum += value;
            min = Math.min(min, value);
            max = Math.max(max, value);
        }
        
        public void printStats() {
            System.out.println("Count: " + count);
            System.out.println("Sum: " + sum);
            System.out.println("Min: " + (count > 0 ? min : "N/A"));
            System.out.println("Max: " + (count > 0 ? max : "N/A"));
        }
    }
    
    StatsConsumer stats = new StatsConsumer();
    IntStream.of(5, 10, 2, 8, 3).forEach(stats);
    stats.printStats();
}

}

This example shows a stateful IntConsumer implementation. The StatsConsumer tracks count, sum, min and max of processed values. While functional, such stateful consumers should be used carefully in parallel streams.

IntConsumer in Collections

IntConsumer can be used with collections containing primitive int values. This example demonstrates processing an int array with a consumer.

Main.java

package com.zetcode;

import java.util.Arrays; import java.util.function.IntConsumer;

public class Main {

public static void main(String[] args) {

    int[] temperatures = {22, 25, 19, 30, 17};
    
    // Consumer that checks for extreme temperatures
    IntConsumer tempChecker = temp -> {
        if (temp > 28) {
            System.out.println("Heat warning: " + temp + "°C");
        } else if (temp < 20) {
            System.out.println("Cold warning: " + temp + "°C");
        }
    };
    
    // Process all temperatures
    Arrays.stream(temperatures).forEach(tempChecker);
    
    // Another example with array modification
    int[] squares = new int[temperatures.length];
    IntConsumer squareStorer = i -> squares[i] = temperatures[i] * temperatures[i];
    for (int i = 0; i < temperatures.length; i++) {
        squareStorer.accept(i);
    }
    System.out.println("Squares: " + Arrays.toString(squares));
}

}

This example shows IntConsumer usage with arrays. The tempChecker analyzes each temperature value. The squareStorer demonstrates how consumers can work with array indices. Consumers provide flexible processing of primitive values.

Combining IntConsumer with Other Functional Interfaces

IntConsumer can be combined with other functional interfaces like IntPredicate or IntFunction to create more complex processing pipelines.

Main.java

package com.zetcode;

import java.util.function.IntConsumer; import java.util.function.IntPredicate;

public class Main {

public static void main(String[] args) {

    // Predicate to check for even numbers
    IntPredicate isEven = n -> n % 2 == 0;
    
    // Consumer for even numbers
    IntConsumer evenProcessor = n -> System.out.println("Even: " + n);
    
    // Consumer for odd numbers
    IntConsumer oddProcessor = n -> System.out.println("Odd: " + n);
    
    // Process numbers with conditional logic
    IntStream.range(1, 6).forEach(n -> {
        if (isEven.test(n)) {
            evenProcessor.accept(n);
        } else {
            oddProcessor.accept(n);
        }
    });
    
    // Another example with IntFunction and IntConsumer
    java.util.function.IntFunction intToString = Integer::toString;
    IntConsumer printHex = n -> System.out.println("Hex: " + Integer.toHexString(n));
    
    IntStream.of(10, 20, 30)
        .mapToObj(intToString)
        .forEach(s -> System.out.println("String: " + s));
        
    IntStream.of(10, 20, 30).forEach(printHex);
}

}

This example shows IntConsumer working with other functional interfaces. The first part demonstrates conditional processing with IntPredicate. The second part shows integration with IntFunction in a stream pipeline. Such combinations enable powerful data processing patterns.

Source

Java IntConsumer Interface Documentation

In this article, we’ve covered the essential methods and features of the Java IntConsumer interface. Understanding these concepts is crucial for efficient processing of primitive int values in functional Java programming.

Author

My name is Jan Bodnar, and I am a dedicated programmer with many years of experience in the field. I began writing programming articles in 2007 and have since authored over 1,400 articles and eight e-books. With more than eight years of teaching experience, I am committed to sharing my knowledge and helping others master programming concepts.

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