Java 102 intro to object-oriented programming in java - exercises

Java 102: Intro to Object-oriented
Programming in Java
Hands-on Exercises

Hands-on Exercise
Creating Objects

Exercise: Creating Objects
• Create a new Java project named Java102
• Create a new package named exercise.carfactory
• Create a class named Car in the exercise.carfactory
package
• Add color, make and model properties to the Car class
• Create a java program named CarFactory (in same
package) that creates two instances of the class Car,
changes their colors to Blue and Pink and prints a message
to the console
• Run the class CarFactory and observe the message in the
Console.

Solution: Creating Objects
package exercise.creatingobjects;
public class Car {
String make;
String model;
String color;
}
package exercise.creatingobjects;
public class CarFactory {
public static void main(String[] args) {
Car firstCar = new Car();
Car secondCar = new Car();
firstCar.color = "Blue";
secondCar.color = "Pink";
System.out.println("Just finished painting new cars");
}
}
Car.java
CarFactory.java

Hands-on Exercise
Working with Methods

Exercise: Working with Methods
• What happens when you compile and run the
following code?
public class Cubes {
static int cube (int i){
int j = i * i * i;
return j;
}
int N = Integer.parseInt(args[0]);
for (int i=0 ;i<= N; i++) {
System.out.println(i + " " + cube(i));
}
}
}

Solution: Working with Methods
public class Cubes {
static int cube (int i){
int j = i * i * i;
return j;
}
int N = Integer.parseInt(args[0]);
for (int i=0 ;i<= N; i++) {
System.out.println(i + " " + cube(i));
}
}
}
% java Cubes 6
0 0
1 1
2 8
3 27
4 64
5 125
6 216

Hands-on Exercise
Method Overloading

Exercise : Method Overloading
• Create a new package named exercise.methodoverloading
• Create a BasicRateTax class with a method calcTax() that returns 20% of a fixed
base income of £1000
• Create a java program named TaxCollector that creates a new BasicRateTax object,
calls the calcTax() method and prints the output to the console
• Run the TaxCollector program and ensure it always prints 200.00 as calculated tax
• Add new calcTax() method to BasicRateTax class that takes a double grossIncome
parameter and calculates the tax as 20% of the grossIncome if it’s greater than the
base income of £1000
• Change the TaxCollector program to call the new calcTax(double grossIncome)
method and passing the gross Income value from the command line
• Run the TaxCollector program and see if the tax is correctly calculated.
• Re-run the program with different Gross Income values and check the output

Solution: Method Overloading
package exercise.methodoverloading;
public class BasicRateTax {
private static final double BASE_INCOME = 1000.00;
private static final double BASIC_TAX_RATE = 0.20;
public double calcTax (){
return BASE_INCOME * BASIC_TAX_RATE;
}
public double calcTax(double grossIncome){
if (grossIncome < BASE_INCOME){
return calcTax();
}
return grossIncome * BASIC_TAX_RATE;
}
}

Solution: Method Overloading
public class TaxCollector {
double grossIncome = Double.parseDouble(args[0]);
BasicRateTax taxCalculator = new BasicRateTax();
double tax = taxCalculator.calcTax(grossIncome);
System.out.println("Tax due is " + tax);
}
}
% java TaxCollector 2000
Tax due is 400.0
Tax due is 2000.0

Exercise: Inheritance
• Create a new package named exercise.inheritance
• Create a class named HigherRateTax in the exercise.inheritance package that
extends BasicRateTax and add an empty calcTax(double grossIncome) method
• Add the code to HigherRateTax.calcTax(double grossIncome) method to calculate
the tax as follows:
– 20% of grossIncome if up to £34,000 (hint: reuse the BasicRateTax.calcTax(double
grossIncom) method)
– 40% of grossIncome if above £34,000 but less than £150,000
– 50% of grossIncome if £150,000 or above
• Run the existing TaxCollector program with some large gross income amounts and
observe that your changes didn’t have any effect on the calculate tax. Why?
• Change the code of the TaxCollector to instantiate HigherRateTax instead of
BasicRateTax
• Run the TaxCollector program again and observe that now the new percentage is
properly applied. You are now using the overridden version of the method
calcTax().

Solution: Inheritance
package exercise.inheritance;
import exercise.methodoverloading.BasicRateTax;
public class HigherRateTax extends BasicRateTax {
public double calcTax(double grossIncome){
double tax = 0.0;
if (grossIncome <=34000.00){
tax = super.calcTax(grossIncome);
}else if (grossIncome > 34000 && grossIncome <=150000) {
tax = grossIncome * 0.40;
}else if (grossIncome > 150000){
tax = grossIncome * 0.50;
}
return tax;
}
}

Solution: Inheritance
import exercise.inheritance.HigherRateTax;
public class TaxCollector {
double grossIncome = Double.parseDouble(args[0]);
BasicRateTax taxCalculator = new HigherRateTax ();
double tax = taxCalculator.calcTax(grossIncome);
System.out.println("Tax due is " + tax);
}
}
Tax due is 20400.0
Tax due is 6400.0
Tax due is 77500.0

Hands-on Exercise
Using a Java Library

Exercise: Using Libraries
• Create a new package named exercise.libraryclient
• Create a class named CardDealer with an empty
deal() method that takes no arguments and returns
a String
• Implement the card dealer to use the StdRandom
library to deal playing cards ramdomly from an
infinite deck of cards
• Create a CardDealerTest program to test the
CardDealer class

Exercise: Using the StdRandom Library
public class CardDealer {
private static final String[] SUITES = { "D", "H", "C", "S"
};
private static final int TOTAL_CARDS_PER_SUITE = 13;
public String deal() {
// select a random suite
String suite = SUITES[StdRandom.uniform(SUITES.length)];
// select a random rank
int rank = StdRandom.uniform (TOTAL_CARDS_PER_SUITE ) +
1;
String card = rank + suite;
// return the dealt card
return card;
}
}

Testing the CardDealer Program
public class CardDealerTest {
CardDealer dealer = new CardDealer();
for (int i=0;i<5;i++){
String card = dealer.deal();
System.out.println( “ Card “ + i + “ is “ + card);
}
}
}

Java 102 intro to object-oriented programming in java - exercises

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