A recursive exponent cacluation calculator for integers, sped up by memo-ization

memo-ized_recursive_exponent_calculator.java

import java.util.Scanner;
import java.util.ArrayList;
import java.util.InputMismatchException;
import java.util.Dictionary;
import java.util.Hashtable;

class Main {
    public static void main(String args[]){
        Scanner beepBoop = new Scanner(System.in);

        int base = -1;
        while(base <= -1) {
            System.out.println("Please enter an integer for the base below the exponent:");
            while(true) {
                try {
                    base = beepBoop.nextInt();
                    if (base < 0) {
                        System.out.println("ERROR: please enter a natural number >= 0");
                        continue;
                    }
                    break;
                } catch (InputMismatchException e) {
                    System.out.println("ERROR: your response was not a natural number. Try again.");
                    beepBoop.next();
                    continue;
                }
            }
        }

        int exponent = -1;
        while(exponent <= -1) {
            System.out.println("Please enter an integer for the exponent:");
            while(true) {
                try {
                    exponent = beepBoop.nextInt();
                    if (exponent < 0) {
                        System.out.println("ERROR: please enter a natural number >= 0");
                        continue;
                    }
                    break;
                } catch (InputMismatchException e) {
                    System.out.println("ERROR: your response was not a natural number. Try again.");
                    beepBoop.next();
                    continue;
                }
            }
        }

        Raiser mahBoy = new Raiser();
        long result = mahBoy.calculate_power(base, exponent);
        System.out.println("Result is: " + Long.toString(result));
    }

}

class Raiser {
    private Dictionary memo_table;
    Raiser() {
        this.memo_table = new Hashtable();
    }

    public long calculate_power(int x, int y) {
        if (y == 1) {
            return x;
        }
        if (y == 0) {
            return 1;
        }
        if (x == 0) {
            return 0;
        }
        if (x == 1) {
            return 1;
        }

        Long iterValue = null;
        Long cached = null;
        int[] tuple = {x, y/2};
        cached = (Long) memo_table.get(tuple);
        if (y % 2 == 0) {
            if (cached != null) {
                iterValue = cached;
            } else {
                iterValue = calculate_power(x, y/2);
                iterValue = iterValue * iterValue;
            }
            int[] pair = {x, y};
            memo_table.put(pair, iterValue);
            return iterValue;
        } else {
            if (cached != null) {
                iterValue = cached;
            } else {
                iterValue = calculate_power(x, y/2);
            }
            iterValue = iterValue * iterValue * x;
            int [] pair = {x, y};
            memo_table.put(pair, iterValue);
            return iterValue;
        }
    }
}