Contents

./Birthday.java

import java.util.GregorianCalendar;

/**
 * Demonstrates use of throwing IllegalArgumentExceptions to prevent errors.
 *
 * @author CSCI209
 */
public class Birthday {
	private int day;
	private int month;

	private static int[] DAYS_IN_MONTH = {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
	
	private static String[] MONTHS = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
	
	/**
	 * Creates a new Birthday object with the given month and day
	 * 
	 * @param month the integer month of the birthday, e.g., January is 1, February is 2
	 * @param day the day of the month of the birthday
	 */
	public Birthday(int month, int day) {
		setBirthday(month, day);
	}

	/**
	 * Returns a String representation of the Birthday as "month/day"
	 * 
	 * @return the Birthday as a string in the format "month/day"
	 */
	@Override
	public String toString() {
		StringBuilder builder = new StringBuilder();
		builder.append(month);
		builder.append("/");
		builder.append(day);
		return builder.toString();
	}

	/**
	 * Rather than setting the month and the day in separate methods, 
	 * this is a better way to implement setting the month and the day. Why?
	 * 
	 * @param month the integer month of the birthday, e.g., January is 1, February is 2
	 * @param day the day of the month of the birthday
	 */
	public void setBirthday(int month, int day) {
		if( month < 1 || month > 12) {
		    throw new IllegalArgumentException("month must be between 1 and 12");
		}
		if( day < 1 || day > 31 ) {
		    throw new IllegalArgumentException("day must be between 1 and 31");
		}
		if( day > DAYS_IN_MONTH[month - 1] ) {
		    throw new IllegalArgumentException( MONTHS[month-1] + " has only " + DAYS_IN_MONTH[month-1] + " days.");
		}
		
		// only set the month and day after we know that 
		// the month and day are valid.
		this.month = month;
		this.day = day;
	}
	
	/**
	 * Returns the day of the month of the Birthday
	 * @return the day of the month of the Birthday
	 */
	public final int getDay() {
		return day;
	}

	/**
	 * Returns the month of the Birthday, where 1 is January, 2 is February, ...
	 * @return the month of the Birthday, where 1 is January, 2 is February, ...
	 */
	public final int getMonth() {
		return month;
	}

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		Birthday b = new Birthday(1, 1);
		System.out.println("New Year's Baby: " + b);
		Birthday leapYearBaby = new Birthday(2, 29);
		System.out.println("Leap Year Baby: " + leapYearBaby);
		
		b.setBirthday(4, 30); // this should work
		System.out.println("End of April birthday: " + b);

		/* 
		 Test calling the method with the exceptions:
		 Each of the statements below, separately, will throw an exception.  
		 Comment out the others to see what one of them does.
		 (Wouldn't it be great if we had a better way to test exceptions?) 
		*/
		b.setBirthday(1,32); 
		b.setBirthday(2,30); 
		b.setBirthday(0, 30);
		Birthday b2 = new Birthday(1, 32);
		
	}

}