The LongConsumer functional interface in Java is part of the java.util.function package and is commonly used for defining operations that consume a single long-valued argument and return no result. It’s a specialization of Consumer for the long primitive type.

The key method in LongConsumer is:

void accept(long value);

Using LongConsumer

Here’s how we can use the LongConsumer functional interface:

1. Lambda Example: We can use a lambda expression to define the action for accept.
2. Method Reference: We can pass a method reference as a LongConsumer.
3. Combine Consumers: We can use the andThen method to chain multiple LongConsumer instances together.

Example 1: Using a Lambda Expression

package org.kodejava.util.function;

import java.util.function.LongConsumer;

public class LongConsumerExample {
    public static void main(String[] args) {
        LongConsumer printLong = value -> System.out.println("Value: " + value);

        // Calling the accept method
        printLong.accept(42L);
        // Output: Value: 42
    }
}

Example 2: Method Reference

We can also use a method reference if we already have a method that accepts a long and performs an operation.

package org.kodejava.util.function;

import java.util.function.LongConsumer;

public class LongConsumerMethodRef {
    public static void main(String[] args) {
        LongConsumer printLong = System.out::println;

        // Calling the accept method
        printLong.accept(100L);
        // Output: 100
    }
}

Example 3: Using andThen to Chain Consumers

The andThen method allows chaining multiple LongConsumer actions. It returns a composite LongConsumer that performs all the operations in sequence.

package org.kodejava.util.function;

import java.util.function.LongConsumer;

public class LongConsumerChaining {
    public static void main(String[] args) {
        LongConsumer printLong = value -> System.out.println("Printing value: " + value);
        LongConsumer doubleValue = value -> System.out.println("Double of value: " + (value * 2));

        LongConsumer combined = printLong.andThen(doubleValue);

        // Calling the combined LongConsumer
        combined.accept(25L);
        // Output:
        // Printing value: 25
        // Double of value: 50
    }
}

Practical Use Case

LongConsumer can be used in scenarios involving streams of long values, such as with the primitive specialization LongStream in the Java Stream API.

package org.kodejava.util.function;

import java.util.function.LongConsumer;
import java.util.stream.LongStream;

public class LongStreamExample {
    public static void main(String[] args) {
        LongConsumer printLong = value -> System.out.print(value + " ");

        // Using LongConsumer with LongStream
        LongStream.range(1, 5).forEach(printLong);
        // Output: 1 2 3 4
    }
}

Key Points:

1. LongConsumer is a functional interface meant for operations on long values.
2. It defines one abstract method, accept(long value).
3. The andThen method is a default method used to chain consumers together.
4. Useful in functional programming styles and with primitive streams like LongStream.