/* ============================================================================
 * File: Factorial.java
 * ----------------------------------------------------------------------------
 *
 * This file is part of the Microsoft Supplemental UI Library for Visual J# .NET
 * Code Samples.
 *
 * Copyright (C)  2003  Microsoft Corporation. All rights reserved.
 *
 * THIS CODE AND INFORMATION ARE PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND,
 * WHETHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A PARTICULAR PURPOSE.
 * ============================================================================
 */

package RecursionDemo;

/**
 * This class implements RecursiveFunction interface to demonstrate calculation of
 * factorial(n) as recursive funtion.
 */
public class Factorial implements RecursiveFunction {
    /**
     * Private variable to store the RecursionStack calling this recursive function.
     */
    private RecursionStack stack;

    /**
     * Returns name of the recursive function
     */
    public String getName() {
        return "Factorial Function";
    }
    
    /**
     * Returns description of the recursive function
     */
    public String getDescription() {
        return "This function generates n! (factorial of n)";
    }

    /**
     * Returns executing code of the recursive function
     */
    public String getCode() {
        return "public int factorial(int n) {\n" +
            "    if (n <= 1)\n" +
            "        return 1;\n" +
            "    else\n" +
            "        return (n * factorial(n - 1));\n" +
            "}";
    }

    /**
     * Does recursion for 'n' steps.  Returns computed value
     */
    public int doRecursion(int n) {
        // push this call into the stack
        stack.push(n);

        int retVal; // value to return
        if (n <= 1) {
            // n <= 1, return 1 i.e. factorial(0) & factorial(1) is 1.
            retVal = 1;
        }
        else {
            // return n * factorial(n - 1);
            retVal = n * doRecursion(n - 1);
        }

        // pop this call out of the stack
        stack.pop(retVal);

        return retVal;
    }

    /**
     * Sets 'stack' as the RecursionStack for this recursive function
     */
    public void setRecursionStack(RecursionStack s) {
        stack = s;
    }
}