Part-3 Functional Interface (Consumer)

Consumer:

• Consumer is an interface in java.
• A functional interface in java.util.function.
• Represents an operation that takes one input and returns nothing.

Core method:
void accept(T t)

Extra Methods in Consumer:
andThen(Consumer after)

• Chains two Consumers together.
• First executes the current Consumer, then executes the after Consumer.

Consumer<String> print = s -> System.out.println(s);
Consumer<String> printUpper = s -> System.out.println(s.toUpperCase());

Consumer<String> combined = print.andThen(printUpper);

combined.accept("hello");
// Output:
// hello
// HELLO

Specialized Consumers:
Java also provides specialized versions of Consumer for different use cases:
BiConsumer<T,U>
-Accepts two inputs, performs an action.

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

printNameAge.accept("Ravi", 25);
// Output: Ravi is 25 years old

Primitive Consumer Interfaces:

Normal Consumer uses objects (like Integer), but when dealing with primitives like int, long, or double, that would cause unnecessary boxing/unboxing. So we have these specialized interfaces to handle primitives efficiently.

1. IntConsumer

Definition: A Consumer that takes an int and performs an action.

IntConsumer printSquare = n -> System.out.println(n * n);
printSquare.accept(5); // Output: 25

2. LongConsumer

Definition: A Consumer that takes a long and performs an action.

LongConsumer printHalf = l -> System.out.println(l / 2);
printHalf.accept(100L); // Output: 50

3. DoubleConsumer

Definition: A Consumer that takes a double and performs an action.

DoubleConsumer printDoubleValue = d -> System.out.println(d * 2);
printDoubleValue.accept(3.5); // Output: 7.0

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