Java.Java8.What is the functional interface BiConsumer?

Let’s talk about BiConsumer<T, U> — it’s part of the java.util.function package and is a functional interface used when you want to perform an action with two inputs and return nothing.

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✅ BiConsumer<T, U>

@FunctionalInterface
public interface BiConsumer<T, U> {
    void accept(T t, U u);
}

It takes two arguments: T and U

Returns void

It’s often used when you want to consume a pair of values (like a key and value), but you don’t need a result

🧠 Example:

BiConsumer<String, Integer> printNameAge = (name, age) ->
    System.out.println(name + " is " + age + " years old");

printNameAge.accept("Alice", 30);
// Output: Alice is 30 years old

🔧 Common Use Case: Iterating over a Map

Map<String, Integer> ages = Map.of("Bob", 25, "Carol", 32);

ages.forEach((name, age) -> System.out.println(name + " => " + age));
// Under the hood, this uses a BiConsumer<String, Integer>

🔗 Chaining BiConsumers

You can chain two BiConsumers using .andThen():

BiConsumer<String, String> greet = (first, last) ->
    System.out.print("Hello, " + first + " " + last);
BiConsumer<String, String> shout = (first, last) ->
    System.out.println("!!!");

greet.andThen(shout).accept("John", "Doe");
// Output: Hello, John Doe!!!

✅ Summary

Interface	Input Types	Return Type	Use Case Example
BiConsumer<T,U>	T, U	void	Map.forEach((k, v) -> ...), logging