Example for using static in a local class for memoization

StaticsInLocalClassesExample.java

package wb.java17;

import java.math.BigInteger;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

public class StaticsInLocalClassesExample {

    public static void main(String[] args) {
        System.out.println(factorial(120));
        System.out.println(factorial(120));
        System.out.println(factorial(121));
    }

    static BigInteger factorial(int n) {
        class Local {
            private static final Map<Integer, BigInteger> CACHE = new ConcurrentHashMap<>();
        }

        if (n == 0) {
            return BigInteger.ONE;
        }

        var nn = Local.CACHE.get(n);
        if (nn != null) {
            return nn;
        }

        var result = BigInteger.valueOf(n).multiply(factorial(n - 1));
        Local.CACHE.put(n, result);
        return result;
    }
}