Java 8 : java.util.function.Supplier Functional Interface

In this article, we will see what is Supplier Functional Interface introduced in Java 8 using examples.

What is java.util.function.Supplier ?

Supplier is a functional interface with a single abstract method get(). This was introduced in Java 8.

@FunctionalInterface public class Supplier<T> {

    public T get();
    
}

 

When to use a Supplier Functional Interface ?

A Supplier is used when you want to generate instances without taking any input.

 

How to use Supplier Functional Interface ?

We can use Supplier to return an instance of a Class as below :

Supplier<SomeClass> supplier = () -> new SomeClass();

 
We could also use constructor reference as follows :

Supplier<SomeClass> supplier = SomeClass::new;

 

Java 8 Supplier Example 1 :

Supplier<String> s1 = () -> "Hello";
System.out.println(s1.get());

Output :

Hello
 

Java 8 Supplier Example 2 :

Supplier<LocalDate> s1 = LocalDate::now;
System.out.println(s1.get());

Output :

2017-05-16
 

Java 8 Supplier Example 3 :

package com.topjavatutorial;

import java.util.function.Supplier;

public class TestSupplier {

  public static void main(String[] args) {
    Person p1 = getPerson(() -> new Person("John"));
    System.out.println(p1.getName());

    Person p2 = getPerson(Person::new);
    System.out.println(p2.getName());
  }

  static Person getPerson(Supplier<Person> supplier) {
    Person p = supplier.get();
    return p;
  }

}

package com.topjavatutorial;

public class Person {
  private String name;

  public Person(String name) {
    this.name = name;
  }

  public Person() {
    this.name = "Dummy";
  }

  public String getName() {
    return name;
  }
}

Output :

John
Dummy

 

Java 8 Primitive Supplier

Java 8 introduced following primitive Supplier functional interfaces :

IntSupplier : Supplier of int-valued results.

Example :

IntSupplier randomInt = new Random()::nextInt;

LongSupplier : Supplier of long-valued results.

DoubleSupplier : Supplier of double-valued results.

BooleanSupplier : Supplier of Boolean-valued results.

 

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