Computational Problem Solving with Java and Interactive Object Graphics

// RandomOvals.java
import java.util.ArrayList;             // Import classes
import java.util.Random;
import doodlepad.*;                     // Import DoodlePad classes

public class RandomOvals {              // public class
                                        // Declare ArrayList of Ovals
    public static ArrayList<Oval> ovals = new ArrayList<>();

                                        // Start of execution
    public static void main(String[] args) {         
        Oval o;                         // Helper variable

        // Fill ArrayList with 20 randomly placed Oval objects
        // Use a while to iterate 20 times
        int i = 0;                      // Init counter
        while (i < 20) {                // While-statement
            o = new Oval();             // Create an Oval object
            o.setMousePressedHandler( RandomOvals::recolor );
            ovals.add( o );             // Add Oval to ArrayList
            i++;                        // Increment counter
        }
    }

    // Event handler method that executes when an Oval is clicked
    public static void recolor(Shape shp, double x, double y, int button) {
        int r, g, b;                    // Helper variables
        Oval o;
        Random rnd = new Random();      // Declare a Random object

        // Loop over all Oval objects and reset to a random fill color
        int i = 0;                      // Init counter
        while ( i < ovals.size() ) {    // While loop
            o = ovals.get(i);           // Get the Oval at index i
            r = rnd.nextInt(256);       // Generate random color components
            g = rnd.nextInt(256);
            b = rnd.nextInt(256);
            o.setFillColor(r, g, b);    // Change fill color
            i++;                        // Increment counter
        }
    }
}

Random rnd = new Random();          // New Random and ArrayList objects
ArrayList<Integer> ints =  new ArrayList<>();

// Fill ArrayList with 1000 random ints
// The int is not boxed in an Integer class before being added
// Java takes care of this for us
int i = 0;                          // Counter
while (i < 1000) {                  // Loop
    ints.add( rnd.nextInt(100) );   // Add int to ArrayList
    i++;                            // Increment counter
}

// Get all ints and print
// Notice how val is assigned without unboxing Integer object
int val;                            // Helper variable
i = 0;                              // Reset counter
while (i < ints.size()) {           // Loop
    val = ints.get( i );            // Get int
    System.out.println( val );      // Print int
    i++;                            // Increment counter
}

// Unique.java
import java.util.HashSet;   // Import class

public class Unique {
  public static void main(String[] args) {
  // Create a HashSet to hold Character objects
  HashSet<Character> letters = new HashSet<>();

  // Add letters as chars, automatically boxed
  letters.add( 'D' );
  letters.add( 'O' );
  letters.add( 'G' );
  letters.add( 'D' );
  letters.add( 'I' );
  letters.add( 'G' );
  letters.add( 'G' );
  letters.add( 'E' );
  letters.add( 'R' );
    
  System.out.println( letters.size() + " unique characters");
  }
}

// Musketeers.java
// The Three Musketeers order dinner
import java.util.ArrayList;
import java.util.HashMap;

public class Musketeers {
  public static void main(String[] args) {
    // The Three Musketeers enter the restaurant: Athos, Porthos and Aramis
    
    // Get ready to take their order.
    HashMap<String, ArrayList<String>> order = 
                            new HashMap<String, ArrayList<String>>();

    // Add a new element for each Musketeer
    order.put("Athos",   new ArrayList<String>());
    order.put("Porthos", new ArrayList<String>());
    order.put("Aramis",  new ArrayList<String>());

    // Athos: I'll have a hamburger
    order.get("Athos").add("Hamburger");      // Get Athos' order and add

    // Porthos: Cheese fries please
    order.get("Porthos").add("Cheese fries"); // Get Porthos' order and add

    // Aramis: Greek Salad
    order.get("Aramis").add("Greek salad");   // Get Aramis' order and add

    // Athos: Nevermind. I'll have the Cobb salad
    order.get("Athos").clear();               // Clear Athos' order
    order.get("Athos").add("Cobb salad");     // Add a Cobb salad

    // Porthos: Tuna sandwich as well
    order.get("Porthos").add("Tuna sandwich"); 
    
    // Aramis: Iced tea too
    order.get("Aramis").add("Iced tea");

    // Athos: Grape juice for me
    order.get("Athos").add("Grape juice");

    // Porthos: Please add a chocolate shake to my order
    order.get("Porthos").add("Chocolate shake");

    // Waiter recounts order
    System.out.println("Athos:");
    for (int i=0; i<order.get("Athos").size(); i++) {
        System.out.println("   " + order.get("Athos").get(i));
    }
    System.out.println("Porthos:");
    for (int i=0; i<order.get("Porthos").size(); i++) {
        System.out.println("   " + order.get("Porthos").get(i));
    }
    System.out.println("Aramis:");
    for (int i=0; i<order.get("Aramis").size(); i++) {
        System.out.println("   " + order.get("Aramis").get(i));
    }
  }
}