MethodReferencesLambda.java

package examples;

import java.util.Optional;
import java.util.function.BinaryOperator;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Supplier;

public class MethodReferencesLambda {

    public static void main(String[] args) {
        // Method references is an another way of writing lambda expressions
        
        // ----------------Example 1 Function--------------
        System.out.println("Simple Lambda Function: ");
        // Functions accept one argument and produce a result.
        Function<Person, Integer> f1 = person -> person.getAge();
        // Method reference lambda (More readable) getAge need not be static method
        Function<Person, Integer> f2 = Person::getAge;
        Person p = new Person("Jack", 28);
        System.out.println(f1.apply(p));
        System.out.println(f2.apply(p));

        // ----------------Example 2 BinaryOperator-------------- 
        System.out.println("Simple Lambda BinaryOperator: ");
        // Accept two argument and produce a result.
        BinaryOperator<Integer> s1 = (i1, i2) -> Integer.sum(i1, i2);
        // Method reference lambda
        BinaryOperator<Integer> s2 = Integer::sum;
        System.out.println(s1.apply(1, 2));
        System.out.println(s2.apply(1, 2));
        
        // ----------------Example 3 Consumer-------------- 
        System.out.println("Simple Lambda Consumer: ");
        // Consumers represent operations to be performed on a single input argument.
        Consumer<String> printer1 = s -> System.out.println(s);
        // Method reference lambda
        Consumer<String> printer2 = System.out::println;
        printer1.accept("This is printer 1");
        printer2.accept("This is printer 2");

        // ----------------Example 4--------------  
        System.out.println("Simple Lambda Supplier: ");
        //Suppliers produce a result of a given generic type
        Supplier<Person> personSupplier1 = () -> new Person();
        // Method reference lambda
        Supplier<Person> personSupplier2 = Person::new;
        System.out.println(personSupplier1.get());
        System.out.println(personSupplier2.get());
 
        // ----------------Example 5 Optional--------------  
        System.out.println("Simple Lambda Optional: ");
        // Optionals are not functional interfaces, but nifty utilities to prevent NullPointerException
        Optional<String> o = Optional.of("bam");
        System.out.println(o.isPresent()); //true
        System.out.println(o.get()); //"bam"
        System.out.println(o.orElse("fallback")); //"bam"
    }

}