Consumer<T>
- Java course
- Advanced
- Lesson 15/82
- 5 min
Learn consumer functions with Consumer<T>.
The Consumer<T> interface
Consumer<T> represents an action that takes a T value and returns nothing (void). Its single abstract method is accept. It is suited for side-effecting operations.
Example: Consumer<String> printer = s -> System.out.println(s);. Then printer.accept("Hello") prints Hello to the screen. Consumer is used to carry value-consuming code as a variable; for example as an argument to forEach.
Chaining Consumers with andThen
To run two Consumers in sequence you use andThen. The first Consumer consumes the value; then the second receives the same value. This is handy for running several actions in a single pass.
Example: printer.andThen(logger).accept("data"). First the value is printed, then it is logged. Both Consumers receive the same value; they run in order. This is a clean way to compose side effects.
Practice Print with a Consumer
Define a Consumer<String> that uses the lambda s -> System.out.println("Got: " + s). Then print the value by calling accept("Hello").
Starter code
import java.util.function.Consumer;
// Define a printing Consumer
// Print the value with accept
// Output: Got: HelloSample solution
import java.util.function.Consumer;
public class ConsumerExample {
public static void main(String[] args) {
Consumer<String> printer = s -> System.out.println("Got: " + s);
printer.accept("Hello");
}
}Expected output
Got: Hello
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which is the call method of Consumer<T>?
- apply
- test
- accept Correct answer
- get
Explanation: accept is Consumer's call method.
2 Complete the Consumer call
Consumer<String> printer = s -> System.out.println(s);
printer.____("Merhaba");Consumer<String> printer = s -> System.out.println(s);
printer.accept("Merhaba");Explanation: accept is Consumer's call method.
3 Match the Consumer concepts
| Term | Meaning |
|---|---|
Consumer<T> |
Takes T returns void |
accept |
Call method |
andThen |
Calls afterwards |
BiConsumer<T,U> |
Takes two values |