1. CS 180 Recitation 9 / {06, 07} / 2007

2. Reminders Assignment 1 was due last night. Assignment 2 is available & due in 1 week. 10:00pm, Wednesday, September 12 Make use of newsgroup Mail to Armand Navabi for Mentor session mailing list [anavabi@cs.purdue.edu]

3. Use of numeric data Use Parentheses –They help reduce errors –Make code more readable Eg: 6 + 15 / 3 or 6 + (15/3) or (6 + 15)/3

4. Operator Overloading When a symbol is used to represent more than one operation – “+” symbol – 6 + 3 = 9 – String output = “hello”+”kitty” Result will be “hellokitty” –“+” symbol is evaluated from left to right

5. Operator Overloading int x = 1; int y = 2; String output = “test” + x + y; output will be test12 String output = x + y + “test” output will be 3test How do we get test3 as the result?

6. Use of Constants Used when value of a variable remains constant Standard Java Convention –Use only capital letters and underscores Makes code more readable Allows user to make changes easily Constants defined in Java API: –Example: PI in Math class (package java.lang)

7. DecimalFormat Class Use DecimalFormat class (package is java.text) to format for numerical outputs double num = 123.45789345; DecimalFormat df = new DecimalFormat(“0.000”); //three decimal places System.out.print(num); System.out.print(df.format(num)); 123.45789345 123.458

8. Escape Characters Use of control characters –Tab \t –Newline \n

9. Math Class Available in java.lang package Make sure you get into the habit of using API for Java 5 Will find methods defined for a wide variety of mathematical and other programming needs

10. Math Class continued MethodInput type Output type Description exp(a) double Return e raised to power a. log(a) double Return natural log of a. floor(a) double Return largest whole number smaller than a. max(a,b) int double … int double … Return larger of a or b. pow(a,b) double Return a raised to power b. sqrt(a) double Return square root of a. sin(a) double Return sine of a(in radians).

11. Math Class Examples: –Formula: s = ut + 1/2 at 2 Code: s = u*t + a*t*t/2.0; –Formula: Code: v = Math.sqrt(3*k*t/(m*p)); –Formula: a = 2 π r 2 + 2 π r h Code: a = 2*Math.PI*r*r + 2*Math.PI*r*h;

12. GregorianCalendar Class Part of java.util.Date package Used to manipulate calendar information GregorianCalendar today, independenceDay; today = new GregorianCalendar(); independenceDay = new GregorianCalendar(1776, 6, 4); //month 6 means July; 0 means January

13. Constants in GregorianCalendar ConstantDescription YEARThe year portion of the calendar date MONTHThe month portion of the calendar date DATEThe day of the month DAY_OF_MONTHSame as DATE DAY_OF_YEARThe day number within the year DAY_OF_MONTHThe day number within the month DAY_OF_WEEKThe day number within the week (Sun --1, Mon -- 2, etc.) WEEK_OF_YEARThe week number within the year WEEK_OF_MONTHThe week number within the month AM_PMThe indicator for AM or PM (AM -- 0, PM -- 1) HOURThe hour in the 12-hour notation HOUR_OF_DAYThe hour in 24-hour notation MINUTEThe minute within the hour

14. Sample Calendar Retrieval GregorianCalendar cal = new GregorianCalendar(); //Assume today is Nov 9, 2003 System.out.print(“Today is ” + (cal.get(Calendar.MONTH)+1) + “/” + cal.get(Calendar.DATE) + “/” + cal.get(Calendar.YEAR)); Today is 11/9/2003 Output

15. Revisit JOption Pane Does this work? age is not a String. It is of type int. How do we handle this? int age; age = JOptionPane.showInputDialog(null, “Enter your age”);

16. Wrapper Classes Wrapper classes are used to perform necessary type conversions, such as converting a String object to a numerical value. int age; String inputStr; inputStr = JOptionPane.showInputDialog( null, “Enter your age”); age = Integer.parseInt(inputStr);

17. Other Conversion Methods Look in Java API to convert from –String to Double –String to Float –String to Long –Hint: You will find conversion from String to Double in the Double class of java.lang package in the API

18. One more time Use the newsgroup Start with Project #2 Mentoring