Consumer in Java

In Java, the Consumer interface is a functional interface defined in the java.util.function package. It represents an operation that takes a single input argument and returns no result. As a functional interface, Consumer can be used for lambda expressions and method references.

1. Single Abstract Method: The Consumer interface defines one abstract method, accept(T t), which takes an argument and performs some operation but does not return any result.
2. Generics: The Consumer interface is generic, allowing you to specify the type of the input object.
3. Usage: Commonly used in scenarios where an operation needs to be performed on an object (such as printing, modifying, etc.) without needing to return a result.
4. Chaining Operations: The Consumer interface also provides the andThen method, allowing you to chain multiple Consumer operations together.

Example

java
Copy code
import java.util.function.Consumer;

public class ConsumerExample {
    public static void main(String[] args) {
        Consumer<String> printConsumer = s -> System.out.println(s);
        printConsumer.accept("Hello, World!"); // Outputs: Hello, World!
    }
}

In this example, printConsumer is a Consumer<String> that takes a string as input and prints it to the console.

andThen Method Example

The andThen method of the Consumer interface can be used to create a sequence of Consumer operations:

java
Copy code
Consumer<String> printConsumer = s -> System.out.println(s);
Consumer<String> printConsumerUpperCase = printConsumer.andThen(s -> System.out.println(s.toUpperCase()));

printConsumerUpperCase.accept("hello"); // First prints "hello", then prints "HELLO"

In this example, printConsumerUpperCase first executes the printConsumer operation (printing the original string) and then executes the operation that converts the string to uppercase and prints it.

Practical Example

Suppose we have a list of strings and we want to print each string. We can use the Consumer interface to accomplish this:

java
Copy code
import java.util.Arrays;
import java.util.List;
import java.util.function.Consumer;

public class ConsumerExample {
    public static void main(String[] args) {
        List<String> strings = Arrays.asList("one", "two", "three");

        Consumer<String> printConsumer = str -> System.out.println(str);
        
        strings.forEach(printConsumer); // Prints each string
    }
}

In this example:

• printConsumer is an implementation of Consumer that takes a string and prints it.
• We use the forEach method to iterate over the list of strings and apply printConsumer to each string (i.e., print each string).

Usage Scenarios

The Consumer interface is commonly used in scenarios where an operation needs to be performed on an object without returning a result, such as iterating over collections to perform operations, executing side effects of functions, etc. Due to its simplicity, it is very common in Java code that follows a functional programming style.