shaikezam.com

Consumer & BiConsumer Java 8 API

21-01-2022 - Shai Zambrovski

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Functional Interfaces

Before Java 8

As an Object-Oriented Programming language, Java has declared almost everthing in the Object model (except for some of the primitive data types and primitive methods).

Functions in Java were only a part of a class and to use them we need to use the Class or to create an instance of it.

From Java 8 onwards

Since Java 8, Java brought us the interface FunctionalInterface:

Conceptually, a functional interface has exactly one abstract method, however, they can include any quantity of default and static methods.

Note that instances of functional interfaces can be created with:

• Lambda expressions.
• Method references
• Constructor references.

The purpose of FunctionalInterface is to make code more readable, clean, and straightforward.

There are many types of FunctionalInterface; Runnable, Callable and so on.

In this tutorial we will learn about the Consumer & BiConsumer FunctionalInterface.

Consumer interface

A FunctionalInterface that can be used when creating lambda expressions or method references (Constructor references irrelevant as Consumer returns nothing) in which accepts an argument and returns nothing.

The Consumer FunctionalInterface has only one method named accept(), also we can chain multiple Consumers with the andThen() method.

Consumer by method references:

public class Main {

    public static void main(String[] args) {
        Consumer<String> toUpperCaseConsumer = Program::print;
        toUpperCaseConsumer.accept("Hello shaikezam.com");
    }

    public static class Program {

        public static void print(String text) {
            System.out.println(text.toUpperCase());
        }
    }

}

Consumer by lambda expressions:

public class Main {

    public static void main(String[] args) {
        Consumer<String> toUpperCaseConsumer = (text) -> System.out.print(text.toUpperCase());
        toUpperCaseConsumer.accept("Hello shaikezam.com");
    }

}

Chain Consumers with andThen() method:

public class Main {

    public static void main(String[] args) {
        Consumer<TextContainer> toUpperCaseConsumer = textContainer -> {
            String text = textContainer.getText();
            textContainer.setText(text.toUpperCase());
        };

        Consumer<TextContainer> printConsumer = textContainer -> System.out.println(textContainer.getText());

        toUpperCaseConsumer
                .andThen(printConsumer)
                .accept(new TextContainer("Hello shaikezam.com"));
    }

    public static class TextContainer {

        private String text;

        public TextContainer(String text) { this.text = text; }

        public String getText() { return text; }

        public void setText(String text) { this.text = text; }
    }

}

For all above examples, the output will be HELLO SHAIKEZAM.COM.

BiConsumer interface

The BiConsumer interface is similar to a Consumer interface and accepts two input parameters (T the 1st parameter and U the 2nd paramater) and does not return any result.

public class Main {

    public static void main(String[] args) {
        BiConsumer<TextContainer, String> toUpperCaseBiConsumer = (textContainer, text) -> {
            textContainer.setText(text.toUpperCase());
        };

        TextContainer textContainer = new TextContainer();

        toUpperCaseBiConsumer.accept(textContainer, "Hello shaikezam.com");

        System.out.println(textContainer.getText());
    }

    public static class TextContainer {

        private String text;

        public String getText() { return text; }

        public void setText(String text) { this.text = text; }
    }

}

And once again, the output will be HELLO SHAIKEZAM.COM.