1. CSE115: Introduction to Computer Science I Dr. Carl Alphonce 219 Bell Hall Office hours: M-F 11:00-11:50 645-4739 alphonce@buffalo.edu

2. Exam 4 Monday (12/6) Exam 4 review Wednesday (12/8) Exam 4 Friday (12/10) Final exam review

3. This week Primitives (floating point numbers) Inheritance (tie up loose ends) Lab discussion –maybe on Friday, if time allows

4. Today Floating point numbers –inexact representation –type casting/coercion If time: –for loop –switch/case

5. Primitives in Java Java has eight primitive types –boolean –integral types: signed: long, int, short, byte unsigned: char –floating point types: double, float Values of the primitive types are not objects –no properties –no capabilities

6. double values: 0.0, 1.0, -3.5, 3141.5926535e-3 inexact representation (!) operations: + - * / 5.0 + 2.0 = 7.0+double X double  double 5.0 – 2.0 = 3.0-double X double  double 5.0 * 2.0 = 10.0*double X double  double 5.0 / 2.0 = 2.5/double X double  double

7. floating point types’ representation both double and float use the IEEE754 representation scheme size of representation differs according to type: –the representation of a float is 4 bytes wide –the representation of a double is 8 bytes wide main point: values of different types have different representations – you can’t “mix and match”!

8. Things to watch for! Representation is inexact –e.g.  has a truncated representation –0.1 does not have an exact representation representation is in terms of powers of 2 Mixing magnitudes –it is possible that x+y is the same as x! 1.0e-15 + 1.0e-15  2.0 e-15 1.0e+15 + 1.0e-15  1.0 e+15 (whoops!) Round-off errors – comparisons! double d = 0.1; double pointNine = d+d+d+d+d+d+d+d+d; pointNine is not the same as 0.9 (whoops!)

9. mixing types in expressions Operators such as +, -, * and / are overloaded: the same name has many different values + overloaded as String concatenation too! “Good” + “ ” + “morning!”  “Good morning!” What happens in an expression which mixes values of different types? 5 + 2.5 = ???? 5 is coerced to its equivalent double value, 5.0: 5.0 + 2.5 = 7.5 Type coercion happens only from “smaller” type to “larger” type (e.g. int  double, not double  int)

10. relational operators We can form expressions like: x < y which have a value of true or false (i.e. the type of this expression is boolean) relational operators: >= == BUT: be careful doing == with floating point numbers!

11. Equality testing Equality testing: –of primitive values: == –of objects: equals method Consider: Foo a = new Foo();Foo c = a; Foo b = new Foo(); what is value ofwhat is value of (a==b)(a==c)