lecture9 - Introduction to Classes Lecture 9 Administrative...

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Unformatted text preview: Introduction to Classes Lecture 9 Administrative Issues • Homework 2 assigned today – Due Thursday, June 5 • Program 2 ongoing – Due Wednesday June 4 • Midterm scheduled for Friday! Homework #1 Review (1/4) • Problem 2.6, parts 4 and 5 int iResult, num1=25, num2=40, num3=17, num4=5; double fResult, val1=17.0, val2=12.78; fResult = num3 / num4; = 17 / 5; = 3; (by integer division) = 3.0; (by assignment conversion) fResult = val1 / num4; = 17.0 / 5; = 17.0 / 5.0; (by arithmetic promotion) = 3.4; Homework #1 Review (2/4) • Problem 2.6, parts 9 and 10 int iResult, num1=25, num2=40, num3=17, num4=5; double fResult, val1=17.0, val2=12.78; fResult = ( double ) num1 / num2; = 25.0 / 40; (by casting) = 25.0 / 40.0; (by arithmetic promotion) = 0.625; fResult = num1 / ( double ) num2; = 25 / 40.0; (by casting) = 25.0 / 40.0; (by arithmetic promotion) = 0.625; fResult = ( double ) (num1 / num2); = 25 / 40; = 0; (by integer division) = 0.0; (by casting) Recall that an if / else statement is a single statement! Homework #1 Review (3/4) • Problem 3.3 if (total == MAX) if (total < sum) System.out.println(“total == MAX and is < sum.”); else System.out.println(“total is not equal to MAX”); if (total == MAX) { if (total < sum) System.out.println(“total == MAX and is < sum.”); } else System.out.println(“total is not equal to MAX”); Homework #1 Review (4/4) • Problem 3.4 if (length = MIN_LENGTH) System.out.println(“The length is minimal.”); (length = MIN_LENGTH) is not a boolean expresssion. The equality operator ( == ) should be used instead of the assignment operator ( = ). Objects • We’ve created and/or used lots of objects – String objects – Random objects • These objects belong to a class – String – Random • So far, all have been part of the Standard Java Library Standard Classes • Until today, we’ve used standard classes • We are ignorant of how they work – Abstraction • Just trust that they work Writing Our Own Classes • Today’s topic: Writing our own classes • But first… – An in-depth look at the concept of objects The World As Objects • Objects exist in the world around us – Desks – Books – Students – Buildings – Trees – Roads – Cars Object Attributes • How would you describe an object? • Example: Car • Car has many characteristics – Model Year – Color – Number of Doors – Weight • There are a Car’s attributes Object Behaviors • A car can do many things – Open a door – Start the ignition – Play a CD – Lock the doors – Accelerate • These define a car’s behavior Objects • All objects are defined by – Attributes (or state ) – Behaviors • An object’s variables define it’s attributes (or state) • Methods define behaviors A Driving Simulator...
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This note was uploaded on 04/15/2009 for the course ASTRONOMY 1000 taught by Professor Kim during the Spring '01 term at Yonsei University.

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lecture9 - Introduction to Classes Lecture 9 Administrative...

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