/*
 * T05n02.java -- Using Assertions to test pre- and post-conditions.
 *
 * Assertions have been added to Java for the purpose of giving Java
 * programmers a slightly nicer way to check for internal logic
 * errors that require program termination.  This program demonstrates
 * the traditional way of handling such problems, and the assertion
 * way of doing it.  Assertions can be used to check all post-conditions,
 * pre-conditions of private methods, as well as other logically problems.
 * Remember that it is NOT appropriate to use assertions to test
 * parameters of a public method of a shared class; throw a more 
 * meaningful exception instead.
 *
 * Special Compilation Instructions:  To use Java's assertion feature,
 *  you must:
 *     * Be using Java 1.4 or higher
 *     * Execute with the flag "-ea" or "-enableassertions"
 *         Ex:  java -ea T05n02
 *       Without "-ea", the program will run as if the assertion statements
 *       don't exist.
 *
 * For you IDE users, again, you'll need to find out how to supply that "-ea"
 * flag when you execute your code.
 */

import java.io.*;

public class T05n02
{
        /* Find the smallest power of two greater than the 
         * given positive integer ceiling.
         * This version uses assertions to check pre-/post-conditions.
         *   Pre:   limit > 0
         *   Post:  returns smallest power of two greater than limit
         */

    static int smallestPowerOf2 (int limit)
    {
        int product = 1;

        assert limit > 0 : "\n\nPre-condition Error: In smallestPowerOf2, "
                         + "limit must be > 0!\n";

        while (product <= limit) {
            product *= 2;              // clearer than the for loop in T05n01?
        }

        assert product/2 <= limit : "\n\nPost-condition Error:  In "
                                  + "smallestPowerOf2, "
                                  + product + "is NOT is smallest power "
                                  + "of 2 greater than " + limit + ".\n";

        return product;
    }


    public static void main (String [] args) 
    {
        int limit,
            powerOf2;

        assert args.length > 0 : "\n\nUsage:  Provide a number on the command "
                               + "line, and I'll find the first\npower of 2 "
                               + "that exceeds it.\n\n";

        limit = Integer.parseInt(args[0]);

        powerOf2 = smallestPowerOf2(limit);

        System.out.println("smallestPowerOf2 says that the smallest power of 2 "
                         + "greater than " + limit + " is " + powerOf2 + ".");
    }
}