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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
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Exam 4 Monday (12/6) Exam 4 review Wednesday (12/8) Exam 4 Friday (12/10) Final exam review
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This week Primitives (floating point numbers) Inheritance (tie up loose ends) Lab discussion –maybe on Friday, if time allows
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Today Floating point numbers –inexact representation –type casting/coercion If time: –for loop –switch/case
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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
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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
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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”!
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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!)
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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)
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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!
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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)
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