I was practicing an algorithmic concept called Recursion. At first, I write a recursive method for calculating Factorial.
A simple solution:
import java.util.Scanner;
public class RecursionFactorial {
public static void main(String[] args) {
try (Scanner in = new Scanner(System.in)) {
int n = in.nextInt();
if(n >=2 && n <=20){
System.out.println(factorial(n));
}
}
}
public static int factorial(int n){
if(n == 1){
return 1;
}else {
return n * factorial(n-1);
}
}
}
The above code satisfied the requirements, but I try to do the same using anonymous lambda based functions and the problem began.
import java.util.Scanner;
import java.util.function.Function;
public class RecursionFactorialJava8 {
public static void main(String[] args) {
try (Scanner in = new Scanner(System.in)) {
int n = in.nextInt();
Function<Integer, Integer> factorial = x -> x==1? x : x * factorial.apply(x - 1);
if (n >= 2 && n <= 20) {
System.out.println(factorial.apply(n));
}
}
}
}
However, this will not work and will produce a compiler error:
The local variable factorial may not have been initialized
Lambdas are most often used to define anonymous functions. A recursive function must call itself. An anonymous lambda can’t call itself since it has no name, so it can’t be recursive.
The problem above is that we are referencing a variable while initializing it. So it is not yet initialized.
After spending a lot time trying to resolve the above error, I found the solution here. https://pysaumont.github.io/2014/09/01/Recursive-lambdas-in-Java-8.html.
import java.util.Scanner;
import java.util.function.Function;
public class RecursionFactorialJava8 {
static final Function<Integer, Integer> factorial = x -> x==1? x : x * RecursionFactorialJava8.factorial.apply(x - 1);
public static void main(String[] args) {
try (Scanner in = new Scanner(System.in)) {
int n = in.nextInt();
if (n >= 2 && n <= 20) {
System.out.println(factorial.apply(n));
}
}
}
}
I just want to let you know about some problems with recursive and Lambdas in Java 8