Java ObjDoubleConsumer Interface

Last modified: April 16, 2025

The java.util.function.ObjDoubleConsumer interface represents an operation that accepts an object-valued and a double-valued argument. It is a functional interface with a single abstract method accept. This interface is useful for operations that need to consume two different types.

ObjDoubleConsumer is part of Java's functional programming utilities added in Java 8. It enables behavior parameterization for operations that work with an object and a double value. The interface doesn't return any result.

ObjDoubleConsumer Interface Overview

ObjDoubleConsumer interface contains one abstract method that performs the operation on the given arguments. Unlike some other functional interfaces, it doesn't provide default methods for composition.

@FunctionalInterface
public interface ObjDoubleConsumer<T> {
    void accept(T t, double value);
}

The code above shows the structure of ObjDoubleConsumer interface. It uses generics where T is the object type parameter. The interface is annotated with @FunctionalInterface to indicate its single abstract method.

Basic ObjDoubleConsumer Usage

The simplest way to use ObjDoubleConsumer is with lambda expressions. We define how to consume the object and double values in the accept method. The example shows a consumer that prints both values.

package com.zetcode;

import java.util.function.ObjDoubleConsumer;

public class Main {

    public static void main(String[] args) {

        // Define a consumer that prints object and double
        ObjDoubleConsumer<String> printer = (s, d) ->
            System.out.println("String: " + s + ", Double: " + d);
        
        // Use the consumer
        printer.accept("Price", 19.99);
        printer.accept("Weight", 2.5);
        
        // Consumer with more complex logic
        ObjDoubleConsumer<String> formatter = (label, value) ->
            System.out.printf("%s: %.2f%n", label, value);
        formatter.accept("Temperature", 23.4567);
    }
}

This example demonstrates basic ObjDoubleConsumer usage with lambda expressions. The printer consumer takes a String and double, printing both. The formatter shows more complex formatting of the double value. Consumers don't return values.

Using ObjDoubleConsumer with Collections

ObjDoubleConsumer can be useful when processing collections where you need to associate objects with double values. This example shows processing a map of product prices.

package com.zetcode;

import java.util.HashMap;
import java.util.Map;
import java.util.function.ObjDoubleConsumer;

public class Main {

    public static void main(String[] args) {

        Map<String, Double> products = new HashMap<>();
        products.put("Laptop", 999.99);
        products.put("Mouse", 25.50);
        products.put("Keyboard", 49.99);
        
        // Consumer to apply discount
        ObjDoubleConsumer<String> discountApplier = (name, price) -> {
            double discounted = price * 0.9; // 10% discount
            System.out.printf("%s: $%.2f -> $%.2f%n", name, price, discounted);
        };
        
        // Apply to all products
        products.forEach(discountApplier::accept);
    }
}

This example shows ObjDoubleConsumer used with a Map. The discountApplier consumer calculates and prints discounted prices. We use method reference syntax with forEach to apply the consumer to all map entries.

ObjDoubleConsumer in Object Processing

We can use ObjDoubleConsumer to modify object properties based on double values. This example demonstrates updating product inventory quantities.

package com.zetcode;

import java.util.function.ObjDoubleConsumer;

class Product {
    String name;
    double quantity;
    
    Product(String name, double quantity) {
        this.name = name;
        this.quantity = quantity;
    }
    
    void display() {
        System.out.printf("%s: %.1f kg%n", name, quantity);
    }
}

public class Main {

    public static void main(String[] args) {

        Product apple = new Product("Apple", 10.5);
        Product banana = new Product("Banana", 7.2);
        
        // Consumer to add to inventory
        ObjDoubleConsumer<Product> addToStock = (p, q) -> p.quantity += q;
        
        // Apply consumer
        addToStock.accept(apple, 2.3);
        addToStock.accept(banana, 1.8);
        
        apple.display();
        banana.display();
    }
}

This example shows ObjDoubleConsumer modifying object state. The addToStock consumer increases product quantities. The consumer directly modifies the Product object's quantity field based on the double value provided.

ObjDoubleConsumer with Primitive Arrays

ObjDoubleConsumer can process arrays where we need to associate objects with double values. This example calculates weighted scores.

package com.zetcode;

import java.util.function.ObjDoubleConsumer;

public class Main {

    public static void main(String[] args) {

        String[] students = {"Alice", "Bob", "Charlie"};
        double[] weights = {0.3, 0.4, 0.3};
        double[] scores = {85.0, 92.0, 78.0};
        
        // Consumer to calculate weighted score
        ObjDoubleConsumer<String> scoreCalculator = (name, weight) -> {
            int index = java.util.Arrays.asList(students).indexOf(name);
            double weighted = scores[index] * weight;
            System.out.printf("%s: %.1f * %.1f = %.1f%n", 
                name, scores[index], weight, weighted);
        };
        
        // Process each student
        for (int i = 0; i < students.length; i++) {
            scoreCalculator.accept(students[i], weights[i]);
        }
    }
}

This example demonstrates ObjDoubleConsumer processing parallel arrays. The scoreCalculator consumer matches each student with their weight and score. It calculates and prints the weighted score for each student.

Combining ObjDoubleConsumer with Other Interfaces

ObjDoubleConsumer can be combined with other functional interfaces for more complex operations. This example shows filtering before consumption.

package com.zetcode;

import java.util.function.ObjDoubleConsumer;
import java.util.function.DoublePredicate;

public class Main {

    public static void main(String[] args) {

        // Consumer for high-value transactions
        ObjDoubleConsumer<String> transactionLogger = (account, amount) ->
            System.out.printf("Large transaction: %s - $%.2f%n", account, amount);
        
        // Predicate to filter high amounts
        DoublePredicate isLarge = amount -> amount >= 1000.0;
        
        // Process transactions
        processTransaction("ACCT-123", 1500.0, isLarge, transactionLogger);
        processTransaction("ACCT-456", 500.0, isLarge, transactionLogger);
    }
    
    static void processTransaction(String account, double amount,
            DoublePredicate filter, ObjDoubleConsumer<String> consumer) {
        if (filter.test(amount)) {
            consumer.accept(account, amount);
        }
    }
}

This example combines ObjDoubleConsumer with DoublePredicate. The processTransaction method only invokes the consumer if the amount passes the filter. This pattern enables flexible composition of operations.

ObjDoubleConsumer in Stream Processing

While not directly used in streams like some other functional interfaces, ObjDoubleConsumer can still be useful in stream pipelines. This example shows processing stream results.

package com.zetcode;

import java.util.function.ObjDoubleConsumer;
import java.util.stream.DoubleStream;

public class Main {

    public static void main(String[] args) {

        // Consumer to accumulate statistics
        class Stats {
            double sum = 0;
            int count = 0;
        }
        Stats stats = new Stats();
        
        ObjDoubleConsumer<Stats> statsUpdater = (s, value) -> {
            s.sum += value;
            s.count++;
        };
        
        // Process stream of doubles
        DoubleStream.of(12.5, 8.3, 15.7, 20.1, 5.4)
            .forEach(d -> statsUpdater.accept(stats, d));
        
        System.out.printf("Count: %d, Sum: %.1f, Avg: %.2f%n",
            stats.count, stats.sum, stats.sum / stats.count);
    }
}

This example uses ObjDoubleConsumer to accumulate statistics from a DoubleStream. The statsUpdater consumer maintains running totals in the Stats object. This shows how consumers can maintain state during stream processing.

Specialized Variants of Consumer

Java provides several specialized consumer interfaces for different combinations of input types. These include BiConsumer, DoubleConsumer, and others for various primitive types.

package com.zetcode;

import java.util.function.BiConsumer;
import java.util.function.DoubleConsumer;
import java.util.function.ObjDoubleConsumer;

public class Main {

    public static void main(String[] args) {

        // ObjDoubleConsumer example
        ObjDoubleConsumer<String> objDoublePrinter = (s, d) ->
            System.out.println(s + ": " + d);
        objDoublePrinter.accept("Value", 3.14);
        
        // BiConsumer example (two generic types)
        BiConsumer<String, Double> biPrinter = (s, d) ->
            System.out.println(s + ": " + d);
        biPrinter.accept("BiValue", 2.71);
        
        // DoubleConsumer example (primitive specialization)
        DoubleConsumer doublePrinter = d ->
            System.out.println("Double: " + d);
        doublePrinter.accept(1.618);
    }
}

This example compares ObjDoubleConsumer with related interfaces. BiConsumer is more general but requires boxing, while DoubleConsumer handles only primitive doubles. Choose based on specific needs.

Source

Java ObjDoubleConsumer Interface Documentation

In this article, we've covered the essential methods and features of the Java ObjDoubleConsumer interface. Understanding these concepts helps in writing expressive code for operations that consume object and double values.

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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