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Supplier Java 8 API

26-01-2022 - 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 Supplier FunctionalInterface.

Supplier interface

A FunctionalInterface that can be used when creating lambda expressions, method references or constructor references, in which accepts no arguments and returns a result.

The Supplier FunctionalInterface has only one method named get() and it isn’t chainable

Supplier by method references:

public class Main {

    public static void main(String[] args) {
        Supplier<String> text = Main::getText;

        System.out.println(text.get());
    }

    public static String getText() {
        return "Hello shaikezam.com";
    }

}

Supplier by lambda expression:

public static void main(String[] args) {
    Supplier<String> text = () -> "Hello shaikezam.com";

    System.out.println(text.get());
}

Supplier by constructor references:

public class Main {

    public static void main(String[] args) {
        Supplier<TextContainer> text = TextContainer::new;

        System.out.println(text.get());
    }

    public static class TextContainer {

        private String text;

        public TextContainer() { text = "Hello shaikezam.com"; }

        @Override
        public String toString() { return text; }
    }

}

For all above examples, the output will be Hello shaikezam.com.