Variables 2b (using your own classes with data)

Level 1 - Basics

We used existing Java classes to create objects until now: Point and Rectangle. But it is also possible to create your own, custom class.

For example, we want to register a product with its price, we could create a class for this with String productName and int priceInCents, and use that in our code.

In IntelliJ, in the project structure, right-click on the src directory in your Exercise, select New > Java Class.
For the name, fill in Product. A new file is created and opened in the editor.
Copy the following code into the file:

public class Product {

    String name;
    int priceInCents;

}

Now switch back to the Application file and copy this into your run() method:

Product product = new Product();
product.name = "Expensive designer lamp";
product.priceInCents = 12000;

Extend this code:

add the product to an ArrayList of Products. Name the arraylist "cart"
create another product and add that to the list as well.

ArrayList<Product> cart = new ArrayList<>();

Product product = new Product();
product.name = "Expensive designer lamp";
product.priceInCents = 12000;
cart.add(product);

Product anotherProduct = new Product();
anotherProduct.name = "Fake turd";
anotherProduct.priceInCents = 520;
cart.add(anotherProduct);

Extend the code so it calculates and shows the total price of the items in the cart. Hint:

start with an int sum,
create a loop that iterates over all the items
in the loop, add the price of that item to the sum

ArrayList<Product> cart = new ArrayList<>();

Product product = new Product();
product.name = "Expensive designer lamp";
product.priceInCents = 12000;
cart.add(product);

Product anotherProduct = new Product();
anotherProduct.name = "Fake turd";
anotherProduct.priceInCents = 520;
cart.add(anotherProduct);

int sum = 0;
for (Product item : cart) {
    sum = sum + item.priceInCents;
}

SaxionApp.printLine("The total is: €" + ((double)sum / 100));

Go back to the file with the Product class. You can see the fields name and priceInCents here. Add a new field shippingCostsInCents with type int.

public class Product {

    String name;
    int priceInCents;
    int shippingCostsInCents;

}

Change your program: set the shipping costs to a value for both of the products that you add to the cart. And also calculate the shipping costs total.

ArrayList<Product> cart = new ArrayList<>();

Product product = new Product();
product.name = "Expensive designer lamp";
product.priceInCents = 12000;
product.shippingCostsInCents = 625;
cart.add(product);

Product anotherProduct = new Product();
anotherProduct.name = "Fake turd";
anotherProduct.priceInCents = 520;
anotherProduct.shippingCostsInCents = 325;
cart.add(anotherProduct);

int sum = 0;
int shipping = 0;
for (Product item : cart) {
    sum = sum + item.priceInCents;
    shipping = shipping + item.shippingCostsInCents;
}

SaxionApp.printLine("The total is: €" + ((double)sum / 100));
SaxionApp.printLine(" plus shipping: €" + ((double)shipping / 100));

Level 2 - Do it yourself

Create a new class Circle with these fields, all ints: x, y, radius, red, green, blue.

In your program, add 150 objects of type Circle to a list. They all should have random values for x, y, radius, red, green and blue. Restrictions:

Keep the values of x and y within the boundaries of your canvas.
Keep the radius between 30 and 100.
Keep the red-green-blue values between 0 and 255.

Finally draw all the circles in the list to the canvas with the correct position, size and color. Use SaxionApp.createColor() to convert r-g-b values to a color. Use SaxionApp.setFill to set the background color of the circles. Use SaxionApp.turnBorderOff() to remove the ugly green border.

// the Circle class (in a separate file)
public class Circle {
    int x;
    int y;
    int radius;
    int red;
    int green;
    int blue;
}

// in your application run() method:
ArrayList<Circle> circles = new ArrayList<>();

while (circles.size() < 150) {
    Circle c = new Circle();
    c.x = SaxionApp.getRandomValueBetween(0, SaxionApp.getWidth());
    c.y = SaxionApp.getRandomValueBetween(0, SaxionApp.getHeight());
    c.radius = SaxionApp.getRandomValueBetween(30, 100);
    c.red = SaxionApp.getRandomValueBetween(0, 255);
    c.green = SaxionApp.getRandomValueBetween(0, 255);
    c.blue = SaxionApp.getRandomValueBetween(0, 255);

    circles.add(c);
}

SaxionApp.turnBorderOff();
for (Circle c : circles) {
    Color color = SaxionApp.createColor(c.red, c.green, c.blue);
    SaxionApp.setFill(color);
    SaxionApp.drawCircle(c.x, c.y, c.radius);
}

Change the program and add three counters. Count the circles that are

mainly blue (blue value larger than the other two values)
mainly red (red value larger than the other two values)
mainly green (you get the idea)

Show all three results afterwards and decide which color won.

ArrayList<Circle> circles = new ArrayList<>();
while (circles.size() < 150) {
    Circle c = new Circle();
    c.x = SaxionApp.getRandomValueBetween(0, SaxionApp.getWidth());
    c.y = SaxionApp.getRandomValueBetween(0, SaxionApp.getHeight());
    c.radius = SaxionApp.getRandomValueBetween(30, 100);
    c.red = SaxionApp.getRandomValueBetween(0, 255);
    c.green = SaxionApp.getRandomValueBetween(0, 255);
    c.blue = SaxionApp.getRandomValueBetween(0, 255);

    circles.add(c);
}

int red = 0;
int green = 0;
int blue = 0;
SaxionApp.turnBorderOff();
for (Circle c : circles) {
    Color color = SaxionApp.createColor(c.red, c.green, c.blue);
    SaxionApp.setFill(color);
    SaxionApp.drawCircle(c.x, c.y, c.radius);

    if (c.red > c.green && c.red > c.blue) {
        red++;
    }
    if (c.green > c.red && c.green > c.blue) {
        green++;
    }
    if (c.blue > c.red && c.blue > c.green) {
        blue++;
    }
}

SaxionApp.print("Counted circles mainly red: " + red);
SaxionApp.print(", mainly green: " + green);
SaxionApp.prinLine(", mainly blue: " + blue);

if (red > green && red > blue) {
    SaxionApp.printLine("RED WON", Color.RED);
}
if (green > red && green > blue) {
    SaxionApp.printLine("GREEN WON", Color.GREEN);
}
if (blue > red && blue > green) {
    SaxionApp.printLine("BLUE WON", Color.BLUE);
}

Level 3 - Objects from data

Classes and data go well together. Data are values stored in a file on disk. One of the formats to store data is the CSV-format. It can store one object per line, the fields are separated with a comma (,) or semicolon (;), depending on the program used to create it.

An example of CSV data for our Circle class:

x;y;radius;red;green;blue
350;350;200;200;200;200
200;200;105;0;0;0
200;200;100;200;200;200
200;200;85;0;0;0
200;200;80;230;200;200
500;200;105;0;0;0
500;200;100;200;200;200
500;200;85;0;0;0
500;200;80;230;200;200
350;350;180;200;200;200
350;340;150;200;0;0
350;320;150;200;200;200
270;300;35;0;0;0
430;300;35;0;0;0
270;300;30;255;255;255
430;300;30;255;255;255
260;290;20;0;0;0
440;300;20;0;0;0
260;290;18;60;0;255
440;300;18;60;0;255
260;290;8;0;0;0
440;300;8;0;0;0
350;350;30;100;100;100

The first line is the field names, the other lines contain values for the fields. Each row defines one circle.

Create a new CSV file in your Exercise:

Copy the CSV data above
Right-click on the Exercise directory > New > File
give the new file the name circles.csv
paste the CSV data into the file
Save it and go back to your program.

The SaxionApp has a builtin CSV reader.

Change your program, so the while loop that creates the circles doesn't use random values, but values from the CSV. Use this example to modify your code:

ArrayList<Circle> circles = new ArrayList<>();

// NOTE: instead of "Exercise1", use the correct Exercise directory name here
// or "Sandbox" if you use the Sandbox project.
CsvReader reader = new CsvReader("Exercise1/circles.csv"); 
reader.setSeparator(';'); // fields separated by semicolon
reader.skipRow(); // skip the header row with field names

while (reader.loadRow()) { // keep looping until there are no more rows

    Circle c = new Circle(); 
    c.x = reader.getInt(0);
    c.y = reader.getInt(1);
    // do the rest of the fields yourself ...

    // add the circle to the arraylist
}

If you do it correctly, you should see a painting that is rumoured to have been made by Van Gogh himself. At least it has the same qualities.

ArrayList<Circle> circles = new ArrayList<>();

CsvReader reader = new CsvReader("Exercise15/circles.csv");
reader.setSeparator(';'); // fields separated by semicolon
reader.skipRow(); // skip the header row with field names
while (reader.loadRow()) {
    Circle c = new Circle();
    c.x = reader.getInt(0);
    c.y = reader.getInt(1);
    c.radius = reader.getInt(2);
    c.red = reader.getInt(3);
    c.green = reader.getInt(4);
    c.blue = reader.getInt(5);

    circles.add(c);
}

// (removed the color counting stuff)
SaxionApp.turnBorderOff();
for (Circle c : circles) {
    Color color = SaxionApp.createColor(c.red, c.green, c.blue);
    SaxionApp.setFill(color);
    SaxionApp.drawCircle(c.x, c.y, c.radius);
}

Level 4 - Class from data

Store this data as CSV-file in your exercise, call it temp.csv.

The data is the average temperature (*10, so 97 means 9.7 degrees) per year in the eastern part of the Netherlands since 1951.

weatherstation;year;temperature
Twente;1951;97
Twente;1952;86
Twente;1953;98 
Twente;1954;88
Twente;1955;86
Twente;1956;79
Twente;1957;97
Twente;1958;93
Twente;1959;102
Twente;1960;94
Twente;1961;97
Twente;1962;78
Twente;1963;76
Twente;1964;89
Twente;1965;83
Twente;1966;92
Twente;1967;97
Twente;1968;88
Twente;1969;85
Twente;1970;85
Twente;1971;91
Twente;1972;85
Twente;1973;90
Twente;1974;93
Twente;1975;93
Twente;1976;92
Twente;1977;93
Twente;1978;87
Twente;1979;78
Twente;1980;85
Twente;1981;91
Twente;1982;97
Twente;1983;96
Twente;1984;86
Twente;1985;78
Twente;1986;85
Twente;1987;83
Twente;1988;99
Twente;1989;104
Twente;1990;104
Twente;1991;91
Twente;1992;102
Twente;1993;90
Twente;1994;101
Twente;1995;98
Twente;1996;78
Twente;1997;97
Twente;1998;98
Twente;1999;105
Twente;2000;105
Twente;2001;99
Twente;2002;103
Twente;2003;99
Twente;2004;99
Twente;2005;101
Twente;2006;108
Twente;2007;107
Twente;2008;101
Twente;2009;100
Twente;2010;85
Twente;2011;103
Twente;2012;98
Twente;2013;94
Twente;2014;113
Twente;2015;105
Twente;2016;102
Twente;2017;105
Twente;2018;111
Twente;2019;110
Twente;2020;113
Twente;2021;101
Twente;2022;113

Create a new program.

Create a class that can hold one object of this temperature CSV-data.
Let the program read the CSV data into objects of the class and add them to a list. Note that this time your are also dealing with a string.

Use the list afterwards to create a diagram:

draw a vertical line for the first year on the left of the screen
let it start at the bottom of the screen
the height has to be as much pixels as the "temperature" value.
for the next year, draw a vertical line right to the previous line
etc.

// class YearTemperature. You probably chose a better name.
public class YearTemperature {
    // there are three columns in the csv, so three fields here
    // the first is a string, the last contain only numbers, so int.
    String weatherStation;
    int year;
    int temp;
}

// in the run() method of the Application:
// (change YearTemperature to your own classname)
ArrayList<YearTemperature> yearTemperatures = new ArrayList<>();

// (change to your own path and file name)
CsvReader reader = new CsvReader("Exercise15/temp.csv");
reader.setSeparator(';'); // fields separated by semicolon
reader.skipRow(); // skip the header row with field names
while (reader.loadRow()) {
    YearTemperature t = new YearTemperature();
    t.weatherStation = reader.getString(0);
    t.year = reader.getInt(1);
    t.temp = reader.getInt(2);

    yearTemperatures.add(t);
}

int x = 10; // little margin on the left
int scale = 3; // to enlarge the graph a bit, otherwise it is such a tiny graph

for (YearTemperature t : yearTemperatures) {
    // draw vertical line 
    SaxionApp.drawLine(x, SaxionApp.getHeight(), x, SaxionApp.getHeight() - t.temp * scale);
    x = x + scale; // move right for the next line
}

Now change the program:

ask the user for a year after 1950, and before 2023
show the graph only from that year on.

// (change YearTemperature to your own classname)
ArrayList<YearTemperature> yearTemperatures = new ArrayList<>();

// (change to your own path and file name)
CsvReader reader = new CsvReader("Exercise15/temp.csv");
reader.setSeparator(';'); // fields separated by semicolon
reader.skipRow(); // skip the header row with field names
while (reader.loadRow()) {
    YearTemperature t = new YearTemperature();
    t.weatherStation = reader.getString(0);
    t.year = reader.getInt(1);
    t.temp = reader.getInt(2);

    yearTemperatures.add(t);
}

int selectedYear = 0;
// keep asking until it is ok
while (selectedYear < 1951 || selectedYear > 2022) {
    SaxionApp.printLine("From which year do you want to see the graph? (1951-2022)");
    selectedYear = SaxionApp.readInt();
}

int x = 10; 
int scale = 3; 

for (YearTemperature t : yearTemperatures) {
    // only draw if it matches our criterium: year should be >= than the selected year
    if (t.year >= selectedYear) {
        SaxionApp.drawLine(x, SaxionApp.getHeight(), x, SaxionApp.getHeight() - t.temp * scale);
        x = x + scale;
    }
}