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# 3.12: Exercises

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The code for this chapter is in the ch12 directory of ThinkJavaCode. See [Section 0.4] for instructions on how to download the repository. Before you start the exercises, we recommend that you compile and run the examples.

Exercise $$\PageIndex{1}$$

Encapsulate the deck-building code from Section 12.6 in a method called makeDeck that takes no parameters and returns a fully-populated array of Cards.

Exercise $$\PageIndex{2}$$

In some card games, Aces are ranked higher than Kings. Modify the compareTo method to implement this ordering.

Exercise $$\PageIndex{3}$$

In Poker a “flush” is a hand that contains five or more cards of the same suit. A hand can contain any number of cards.

1. Write a method called suitHist that takes an array of cards as a parameter and that returns a histogram of the suits in the hand. Your solution should only traverse the array once.
2. Write a method called hasFlush that takes an array of cards as a parameter and returns true if the hand contains a flush (and false otherwise).

Exercise $$\PageIndex{4}$$

Working with cards is more interesting if you can display them on the screen. If you have not already read Appendix B about 2D graphics, you should read it before working on this exercise. In the code directory for this chapter, ch12, you will find:

• cardset-oxymoron: A directory containing images of playing cards.
• CardTable.java: A sample program that demonstrates how to read and display images.

This code demonstrates the use of a 2D array, specifically an array of images. The declaration looks like this:

private Image[][] images;


The variable images refers to a 2D array of Image objects, which are defined in the java.awt package. Here’s the code that creates the array itself:

images = new Image[14][4];


The array has 14 rows (one for each rank plus an unused row for rank 0) and 4 columns (one for each suit). Here’s the loop that populates the array:

String cardset = "cardset-oxymoron";
String suits = "cdhs";

for (int suit = 0; suit <= 3; suit++) {
char c = suits.charAt(suit);

for (int rank = 1; rank <= 13; rank++) {
String s = String.format("%s/%02d%c.gif",
cardset, rank, c);
images[rank][suit] = new ImageIcon(s).getImage();
}
}


The variable cardset contains the name of the directory that contains the image files. suits is a string that contains the single-letter abbreviations for the suits. These strings are used to assemble s, which contains the filename for each image. For example, when rank=1 and suit=2, the value of s is "cardset-oxymoron/01h.gif", which is an image of the Ace of Hearts.

The last line of the loop reads the image file, extracts an Image object, and assigns it to a location in the array, as specified by the indexes rank and suit. For example, the image of the Ace of Hearts is stored in row 1, column 2.

If you compile and run CardTable.java, you should see images of a deck of cards laid out on a green table. You can use this class as a starting place to implement your own card games.

This page titled 3.12: Exercises is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by Allen B. Downey (Green Tea Press) .

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