Lecture 4
Classes and Objects
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Classes and Objects - Introduction to Programming in Java - Lecture Slides, Slides of Java Programming
In this course, Introduction to Programming in Java, we learned all programming concepts and implement them in java. Key points in these lecture slides are: Classes and Objects, Solutions, Minvalue, Minindex, Values, Array Index, Array Value, Popular Issues, Indexes, Print
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2012/2013
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Lecture 4
Classes and Objects
Review
Solutions 2
public static int getSecondMinIndex(int[] values) {
int secondIdx = -1;int minIdx= getMinIndex(values); for(int i=0; i<values.length; i++) {
if (i == minIdx)
continue; if (secondIdx == -1 ||
values[i] < values[secondIdx])^ secondIdx = i;
} return secondIdx; } •^ What happens if values = {0}? values = {0, 0}? values = {0,1}?
Popular Issues 1
•^ Array Index vs Array Value^ int[] values = {99, 100, 101};System.out.println(values[0] );
// 99
Values
Indexes
2 Docsity.com
Popular Issues 3
•^ Variable initialization^ int getMinValue(int[] vals) {
int min = 0;for (int i = 0; i < vals.length; i++) {^ if (vals[i] < min) {
min = vals[i] } } }
Problem?
•^ What if
vals = {1,2,3}
•^ Set
min = Integer.MAX_VALUE
or
vals[0]Docsity.com
Popular Issues 4
•^ Variable Initialization – secondMinIndex^ int minIdx = getMin(vals)int secondIdx = 0;for (int i = 0; i < vals.length; i++) {
if (i == minIdx) continue;if (vals[i] < vals[secondIdx])
secondIdx = i;
} • What if vals = {0, 1, 2}? • See solutions
Debugging Notes 1
•^ Use System.out.println throughout your codeto see what it’s doing^ for ( int i=0; i< vals.length; i++) {^ if ( vals[i] < minVal) {
System.out.println(“cur min: ”
- minVal);
System.out.println(“new min: ” + vals[i]);minVal = vals[i]; } }
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Debugging Notes 2
•^ Formatting •^ Ctrl-shift-f is your friend^ for (int i
= 0; i < vals.length; i++) { if^
(vals[i] < vals[minIdx]) {
minIdx=i;}return minIdx;} • Is there a bug? Who knows! Hard to read
Today’s Topics
Object oriented programming
Defining ClassesUsing ClassesReferences vs Values
Static types and methods
Object oriented programming
•^ Represent the real world
Baby
Object Oriented Programming
•^ Objects group together^ –
Primitives (int, double, char, etc..) – Objects (String, etc…)
Baby
String nameboolean isMaledouble weightdouble decibelsint numPoops
Why use classes?
•^ Why not just primitives?
// little baby alex String nameAlex;double weightAlex; // little baby david String nameDavid;double weightDavid;
Why use classes?
•^ Why not just primitives?
// little baby alex String nameAlex;double weightAlex; // little baby david String nameDavid;double weightDavid; // little baby david String nameDavid2;double weightDavid2;
David2?Terrible
500 Babies?
That Sucks!
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