Supplier Functional Interface

In this lesson, we will look at the supplier functional interface.

We'll cover the following

Supplier is an interface that does not take in any argument but produces a value when the get() function is invoked. Suppliers are useful when we don’t need to supply any value and obtain a result at the same time.

Below are some of the functional interfaces, which can be categorized as a supplier.

Interface Name Description Abstract Method
Supplier<T> Represents a supplier of results (reference type) T get()
DoubleSupplier A supplier of double-value results double getAsDouble()
IntSupplier A supplier of int-value results int getAsInt()
LongSupplier A supplier of long-value results long getAsLong()
BooleanSupplier A supplier of boolean-value results boolean getAsBoolean()

Supplier<T>

The Supplier<T> interface supplies a result of type T. In the previous lesson, we were passing a person object and a predicate to our isPersonEligibleForVoting() method.

In this example, we will provide a Supplier<Person> instead of the Person object. The isPersonEligibleForVoting() method will, itself, fetch the Person object from the supplier. Here is the code for this.

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import java.util.function.Predicate;

import java.util.function.Supplier;



public class SupplierTest {



  static boolean isPersonEligibleForVoting(

      Supplier<Person> supplier, Predicate<Person> predicate) {

    return predicate.test(supplier.get());

  }



  public static void main(String args[]) {

    Supplier<Person> supplier = () -> new Person("Alex", 23);

    Predicate<Person> predicate = (p) -> p.age > 18;

    boolean eligible =

        isPersonEligibleForVoting(supplier, predicate);

    System.out.println("Person is eligible for voting: " + eligible);

  }

}



class Person {

  String name;

  int age;



  Person(String name, int age) {

    this.name = name;

    this.age = age;

  }

}

The Supplier<T> interface does not contain any default or static methods. Let us look at some of the primitive specializations of the supplier interface.

IntSupplier

The IntSupplier interface has a method getAsInt(), which applies the given operation on its argument and returns an int value. It is similar to using an object of type Supplier<Integer>.

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import java.util.function.IntSupplier;



public class SupplierDemo {



  public static void main(String args[]) {

    

        IntSupplier supplier = () -> (int)(Math.random() * 10); 



        System.out.println(supplier.getAsInt()); 

  }

}

DoubleSupplier

The DoubleSupplier interface has a method getAsDouble(), which applies the given operation on its argument and returns a double value. It is similar to using an object of type Supplier<Double>.

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import java.util.function.DoubleSupplier;
public class SupplierDemo {
  public static void main(String args[]) {
    
        DoubleSupplier supplier = () -> (int)(Math.random() * 10); 
        System.out.println(supplier.getAsDouble()); 
  }
}
1

What does T represent in Supplier<T> ?

A)

The type of input parameter

B)

The return type

C)

None of the above

Question 1 of 20 attempted

In the next lesson, we will look at the Consumer functional interfaces. These interfaces are the opposite of suppliers.

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