CSE115: Introduction to Computer Science I Dr. Carl Alphonce 219 Bell Hall Office hours: M-F 11:00-11:

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

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

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

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

double values: 0.0, 1.0, -3.5, e-3 inexact representation (!) operations: + - * / = 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

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”!

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 e-15  2.0 e e e-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!)

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 is coerced to its equivalent double value, 5.0: = 7.5 Type coercion happens only from “smaller” type to “larger” type (e.g. int  double, not double  int)

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!

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)