Method Referencing

Method reference is feature related to lambda expressions. Method references are more readable form of Lambda expressions for already written methods. :: operator is used to define method reference. It provides a way to a method without executing it. In order to that a method reference requires a target type context that consists of a compatible functional interface.

Method reference when evaluated creates an instance of the functional interface. The 2 types of method references are:-

a). Static Method References.

Syntax:-  ClassName :: methodName

Ex:-

public interface Parent
{
        String process(String input);
}

public class MethodReference
{
        public static String toUpperStatic(String input)
        {
                return input.toUpperCase();
         }



      public static void main(String... args)
        {
             Parent parent = Parent::toUpperStatic;
     System.out.println("Static reference = "+parent .process("static"));
             }
}

b). Instance Method References Of Objects.

Syntax:-   objRef :: methodName

Ex:-

public interface Parent
    {
            String process(String input);
    }

    public class MethodReference
    {
            public String toUpperInstance(String input)
            {
                    return input.toUpperCase();
           }


          public static void main(String... args)
            {
                MethodReference methodReference = new MethodReference();
                     Parent parent  = methodReference::toUpperInstance;
             System.out.println("Instance reference  "+parent .process("instance"));
                 }
    }

Constructor Referencing

you can create references to the constructors. In Constructor references the method name is "new" and the receiver is always the name of the class that is defining the constructor. You can assign a constructor reference to any functional interface which has a method compatible with the constructor.

Syntax:-    ClassName :: new 

Ex:-

package com.evon;

    @FunctionalInterface
    public interface MyString
    {

            String strFunc(char[] chArray);
    }

    public class StringCreator 
    {

          public static void main(String[] args) 
        {
                    MyString mystr = String::new;

                    char[] charArray = {'e','v','o','n','t','e','c','h','n','o','l','o','g','y'};

                    System.out.println(mystr.strFunc(charArray));

        }

    }

In above example we have assigned a String constructor reference to the functional interface which we have created just now.

Hope this will help you :)