Java Lambda Expression Predefined Functional Interfaces

Introduction

Java defines many functional interfaces in java.util.function packages:

Interface Purpose
UnaryOperator<T>Apply a unary operation to an object of type T and return the result, which is of type T. Its method is called apply (?).
BinaryOperator<T> Apply an operation to two objects of type T and return the result, which is of type T. Its method is called apply(?).
Consumer<T>Apply an operation on an object of type T. Its method is called accept(?).
Supplier<T>Return an object of type T. Its method is called get(?).
Function<T, R> Apply an operation to an object of type T and return the result as an object of type R. Its method is called apply(?).
Predicate<T>Determine if an object of type T fulfills some constraint. Its method is called test(?). 

import java.util.function.Function;

public class Main {
  public static void main(String args[]) {
    Function<Integer, Integer> factorial = (n) -> {
      int result = 1;
      for (int i = 1; i <= n; i++) {
        result = i * result;//from  w  w  w  .j  ava2s . c  o  m
      }
      return result;
    };

    System.out.println("The factoral of 3 is " + factorial.apply(3));
    System.out.println("The factoral of 5 is " + factorial.apply(5));
  }
}



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