Java.Java8.What are the functional interfaces ObjDoubleConsumer, ObjIntConsumer, and ObjLongConsumer?

These interfaces:

• Take two arguments: one of a generic object type T and one primitive (double, int, or long)
• Return nothing (void)
• Are used when you want to perform an action (consume values), without boxing the primitive

✅ 1. ObjDoubleConsumer<T>

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

🧠 Example:

ObjDoubleConsumer<String> printPrice = (product, price) ->
    System.out.println(product + " costs $" + price);

printPrice.accept("Coffee", 4.99); // Output: Coffee costs $4.99

✅ 2. ObjIntConsumer<T>

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

🧠 Example:

ObjIntConsumer<String> printQuantity = (item, quantity) ->
    System.out.println(quantity + " x " + item);

printQuantity.accept("Apples", 5); // Output: 5 x Apples

✅ 3. ObjLongConsumer<T>

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

🧠 Example:

ObjLongConsumer<String> logTimestamp = (event, timestamp) ->
    System.out.println("[" + timestamp + "] Event: " + event);

logTimestamp.accept("UserLogin", System.currentTimeMillis());

🔧 Why Use These?

Feature	Value
✅ Avoid boxing	No Integer, Double, or Long objects needed
✅ Stream-friendly	Often used in custom collectors, batch processors, etc.
✅ Descriptive	Makes it clear you’re working with an object and a primitive

🔄 Summary Table

Interface	Parameters	Return	Description
ObjDoubleConsumer<T>	T, double	void	Consumes an object and a double
ObjIntConsumer<T>	T, int	void	Consumes an object and an int
ObjLongConsumer<T>	T, long	void	Consumes an object and a long

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✅ Real Use Case?

Suppose you’re processing a product and want to log how many units were sold:

ObjIntConsumer<Product> logSale = (product, qty) -> 
    System.out.println("Sold " + qty + " units of " + product.getName());