1. CS 18000 Problem Solving and Object Oriented Programming Spring 2019
Section LE2
Week 6: Lecture 11, February
Slides updated: 5:15pm, February
Aditya Mathur
Professor, Department of Computer Science
Purdue University
West Lafayette, IN, USA

2. Review Arrays Example Class public class Car{ } Method: Declaration
public int getMiles(){}
Method: Arguments
public int selectCar(Car c1, Car c2){}
Method: Input and output
Car c=selectCar(momsCar, dadsCar);
2/13/2019
CS 180. Spring Week 6

3. Today Modifiers: default, public, private, static
get() and set() methods
Methods: Passing parameters
Variable sized arrays: ArrayList
2/13/2019
CS 180. Spring Week 6

4. Classes: Instance variables
momsCar=new Car(“Ferrari”, “Spider”, 120);
public class Car{
String make;
String model;
int miles;
methods }
make =“Ferrari”;
model=“Spider”
miles=120
methods
Object: momsCar
Instance variables
Belong to an object
dadsCar=new car(“Chevy”, “Impala”, );
make =“Chevy”;
model=“Impala”
miles=100000
methods
Object: dadsCar
2/13/2019
CS 180. Spring Week 6

5. Classes: Static variables/methods
momsCar=new Car(“Ferrari”, “Spider”, 120);
public class Car{
static String make;
String model;
int miles;
methods }
Replaced by “Chevy”
make =“Ferrari”;
model=“Spider”
miles=120
methods
Object: momsCar
Class variable
(only one copy)
Instance variables
Belong to an object
dadsCar=new car(“Chevy”, “Impala”, );
make =“Chevy”;
model=“Impala”
miles=100000
methods
Object: dadsCar
2/13/2019
CS 180. Spring Week 6

6. Classes: private and public
public class Car{
private String make;
String model;
int miles;
methods }
momsCar=new Car(“Ferrari”, “Spider”, 120);
Instance variables
Belong to an object
make =“Ferrari”;
model=“Spider”
miles=120
methods
Object: momsCar
String model=momsCar.model;
int miles=momsCar.miles;
int make=momsCar.make;
2/13/2019
CS 180. Spring Week 6

7. Classes: Summary of modifiers
Access
public
All packages in the program
private
Within a class
(none) default
Within a package
static
Class variable/method; common to objects of a class
2/13/2019
CS 180. Spring Week 6

8. Classes: get() methods
public class Car{
private String make;
String model;
int miles;
methods }
momsCar=new Car(“Ferrari”, “Spider”, 120);
make =“Ferrari”;
model=“Spider”
miles=120
methods
Object: momsCar
public String getModel(){
return (model); }
String model=momsCar.getModel();
int miles=momsCar.getMiles();
int make=momsCar.getMake();
2/13/2019
CS 180. Spring Week 6

9. Classes: set() methods
public class Car{
private String make;
String model;
int miles;
methods }
momsCar=new Car( );
make =“Ferrari”;
model=“Spider”
miles=120
methods
Object: momsCar
public void setModel(String m){
model=m; }
momsCar.setModel(“Spider”);
momsCar.setMiles(0);
momsCar.setMake(“Ferrari”);
2/13/2019
CS 180. Spring Week 6

10. Methods: Declaration Arguments Access
public static void sort(double [] data){
Body }
Return type
Find if a given point (x,y) is inside a circle of radius r and centered at the origin (0,0).
public boolean inCircle(double r, double x, double y){ }
2/13/2019
CS 180. Spring Week 6

11. Methods: Parameter passing
public boolean inCircle(double radius, double x, double y){ }
double r=3.5, x=2.0, y=1.0;
boolean pointInCircle= inCircle(r, x, y);
Values of r, x, y are passed to inCircle.
2/13/2019
CS 180. Spring Week 6

12. Methods: Parameter passing
public boolean inCircle(double radius, double x, double y){ }
double [] data=new double [10];
double val=21;
public void init(val, data);
Value of “val” is passed to init().
Address of “data” is copied into a local variable and passed to init(). Thus, a value, that happens to be an address, is passed.
Explain using an example.
2/13/2019
CS 180. Spring Week 6

13. Methods: Passing arrays
public int [] data=new int [4]; // Array of ints
public void test(int [] d){. …. } // Method that takes an array as input
test(data);// Calling test
dataTemp
data 10 20 -2 5 1 2 3
A copy of the pointer to the first element of the array is passed to “test”.
2/13/2019
CS 180. Spring Week 6

14. ArrayList ArrayList enables creation of resizable arrays.
Create an array of size 0.
Add and remove elements
Sort the array.
2/13/2019
CS 180. Spring Week 6

15. ArrayList
ArrayList<String> carMake=new ArrayList<String>();
carMake.add(“Ford”); // Add an element
carMake.add(“Mazda”); // and another element
printCars(); // Print the array (two elements)
carMake.remove(0); // Remove car at index 1
printCars(); // Print again (only one element at index 0
carMake.add(“Toyota”); // and another element
carMake.add(“Buick”); // and another element
Collections.sort(carMake); // Sort cars in carMake array
printCars(); // Print again (three cars)
Explain using an example.
2/13/2019
CS 180. Spring Week 6

16. Week 6: Lecture 11 Feb 13, 2019 Questions? Contact your TA. 2/13/2019
CS 180. Spring Week 6