18.10 Locating Resources Using the URL Class

Chapter Summary 637

85

86public void stop() {

87timer.stop();

A label is created in line 17 to display a flag image. An array of flag images for seven nations is created in lines 26–27. An array of audio clips is created in lines 28–29. Each audio clip is created for an audio file through the URL of the current class. The audio files are stored in the same directory with the applet class file.

The combo box for country names is created in lines 20–21. When a new country name in the combo box is selected, the current presentation is stopped and a new selected nation is presented (lines 52–55).

The presentNation(index) method (lines 73–79) presents a nation with the specified index. It sets a new image in the label (line 74), synchronizes with the combo box by setting the selected index (line 75), plays the new audio, and sets a new delay time (line 78).

The applet’s start and stop methods are overridden to resume and suspend the animation (lines 81–89).

KEY TERMS

CHAPTER SUMMARY

1.JApplet is a subclass of Applet. It is used for developing Java applets with Swing components.

2.The applet bytecode must be specified, using the <applet> tag in an HTML file to tell the Web browser where to find the applet. The applet can accept string parameters from HTML using the <param> tag.

3.The applet container controls and executes applets through the init, start, stop, and destroy methods in the Applet class.

4.When an applet is loaded, the applet container creates an instance of it by invoking its no-arg constructor. The init method is invoked after the applet is created. The start method is invoked after the init method. It is also called whenever the applet becomes active again after the page containing the applet is revisited. The stop method is invoked when the applet becomes inactive.

5.The destroy method is invoked when the browser exits normally to inform the applet that it is no longer needed and should release any resources it has allocated. The stop method is always called before the destroy method.

Programming Exercises 641

18.6** (Game: TicTacToe) Rewrite the program in §18.9, “Case Study: TicTacToe,” with the following modifications:

■Declare Cell as a separate class rather than an inner class.

■Add a button named New Game, as shown in Figure 18.17(b). The New Game button starts a new game.

18.7** (Financial application: tax calculator) Create an applet to compute tax, as shown in Figure 18.17(c). The applet lets the user select the tax status and enter the taxable income to compute the tax based on the 2001 federal tax rates, as shown in Exercise 10.8.

18.8*** (Creating a calculator) Use various panels of FlowLayout, GridLayout, and BorderLayout to lay out the following calculator and to implement addition (+), subtraction (-), division (/), square root (sqrt), and modulus (%) functions (see Figure 18.18(a)).

FIGURE 18.18 (a) Exercise 18.8 is a Java implementation of a popular calculator. (b) Exercise 18.9 converts between decimal, hex, and binary numbers.

18.9* (Converting numbers) Write an applet that converts between decimal, hex, and binary numbers, as shown in Figure 18.18(b). When you enter a decimal value on the decimal-value text field and press the Enter key, its corresponding hex and binary numbers are displayed in the other two text fields. Likewise, you can enter values in the other fields and convert them accordingly.

18.10**(Repainting a partial area) When you repaint the entire viewing area of a panel, sometimes only a tiny portion of the viewing area is changed. You can improve the performance by repainting only the affected area, but do not invoke super.paintComponent(g) when repainting the panel, because this will cause the entire viewing area to be cleared. Use this approach to write an applet to display the temperatures of each hour during the last 24 hours in a histogram. Suppose that temperatures between 50 and 90 degrees Fahrenheit are obtained randomly and are updated every hour. The temperature of the current hour needs to be redisplayed, while the others remain unchanged. Use a unique color to highlight the temperature for the current hour (see Figure 18.19(a)).

18.11** (Simulation: a running fan) Write a Java applet that simulates a running fan, as shown in Figure 18.19(b). The buttons Start, Stop, and Reverse control the fan. The scrollbar controls the fan’s speed. Create a class named Fan, a subclass of JPanel, to display the fan. This class also contains the methods to suspend and resume the fan, set its speed, and reverse its direction. Create a class named FanControl that contains a fan, and three buttons and a scroll bar to control the fan. Create a Java applet that contains an instance of FanControl.

Programming Exercises 643

FIGURE 18.22 Three clocks run independently with individual control and group control.

should continuously enlarge by 1 in width and 1 in height until it reaches a width of 300 and a height of 300. The viewing area should shrink and enlarge (alternately) to create animation for the single image.

18.16*** (Simulating a stock ticker) Write a Java applet that displays a stock-index ticker (see Figure 18.23). The stock-index information is passed from the <param> tag in the HTML file. Each index has four parameters: Index Name (e.g., S&P 500), Current Time (e.g., 15:54), the index from the previous day (e.g., 919.01), and Change (e.g., 4.54). Use at least five indexes, such as Dow Jones, S&P 500, NASDAQ, NIKKEI, and Gold & Silver Index. Display positive changes in green and negative changes in red. The indexes move from right to left in the applet’s viewing area. The applet freezes the ticker when the mouse button is pressed; it moves again when the mouse button is released.

FIGURE 18.23 The program displays a stock-index ticker.

18.17** (Racing cars) Write an applet that simulates four cars racing, as shown in Figure 18.24(a). You can set the speed for each car, with 1 being the highest.

FIGURE 18.24 (a) You can set the speed for each car. (b) This applet shows each country’s flag, name, and description, one after another, and reads the description that is currently shown.

18.18** (Showing national flags) Write an applet that introduces national flags, one after the other, by presenting each one’s photo, name, and description (see Figure 18.24(b)) along with audio that reads the description.

644 Chapter 18 Applets and Multimedia

Suppose your applet displays the flags of eight countries. Assume that the photo image files, named flag0.gif, flag1.gif, and so on, up to flag7.gif, are stored in a subdirectory named image in the applet’s directory. The length of each audio is less than 10 seconds. Assume that the name and description of each country’s flag are passed from the HTML using the parameters name0, name1, Á , name7, and description0, description1, Á , and description7. Pass the number of countries as an HTML parameter using numberOfCountries. Here is an example:

<param name = "numberOfCountries" value = 8> <param name = "name0" value = "Canada">

<param name = "description0" value = "The Maple Leaf flag The Canadian National Flag was adopted by the Canadian Parliament on October 22, 1964 and was proclaimed into law by Her Majesty Queen Elizabeth II (the Queen of Canada) on February 15, 1965. The Canadian Flag (colloquially known as The Maple Leaf Flag) is a red flag of the proportions two by length and one by width, containing in its center a white square, with a single red stylized eleven-point maple leaf centered in the white square.">

Hint: Use the DescriptionPanel class to display the image, name, and the text. The DescriptionPanel class was introduced in Listing 17.6.

18.19*** (Bouncing balls) The example in §18.8 simulates a bouncing ball. Extend the example to allow multiple balls, as shown in Figure 18.25(a). You may use the + 1 or - 1 button to increase or decrease the number of the balls, and use the Suspend and Resume buttons to freeze the balls or resume bouncing. For each ball, assign a random color.

FIGURE 18.25 (a) The applet allows you to add or remove bouncing balls. (b) Click Play to play an audio clip once, click Loop to play an audio repeatedly, and click Stop to terminate playing.

18.20* (Playing, looping, and stopping a sound clip) Write an applet that meets the following requirements:

■Get an audio file. The file is in the class directory.

■Place three buttons labeled Play, Loop, and Stop, as shown in Figure 18.25(b).

■If you click the Play button, the audio file is played once. If you click the Loop button, the audio file keeps playing repeatedly. If you click the Stop button, the playing stops.

■The applet can run as an application.

Programming Exercises 645

18.21** (Creating an alarm clock) Write an applet that will display a digital clock with a large display panel that shows hour, minute, and second. This clock should allow the user to set an alarm. Figure 18.26(a) shows an example of such a clock. To turn on the alarm, check the Alarm check box. To specify the alarm time, click the Set alarm button to display a new frame, as shown in Figure 18.26(b). You can set the alarm time in the frame.

FIGURE 18.26 The program displays current hour, minute, and second and enables you to set an alarm.

18.22** (Creating an image animator with audio) Create animation using the applet (see Figure 18.27) to meet the following requirements:

■Allow the user to specify the animation speed. The user can enter the speed in a text field.

■Get the number of frames and the image file-name prefix from the user. For example, if the user enters n for the number of frames and L for the image prefix, then the files are L1, L2, and so on, to Ln. Assume that the images are stored in the image directory, a subdirectory of the applet’s directory.

■Allow the user to specify an audio file name. The audio file is stored in the same directory as the applet. The sound is played while the animation runs.

FIGURE 18.27 This applet lets the user select image files, audio file, and animation speed.

18.23** (Simulation: raising flag and playing anthem) Create an applet that displays a flag rising up, as shown in Figure 15.1. As the national flag rises, play the national anthem. (You may use a flag image and anthem audio file from Listing 18.13.)

Comprehensive

18.24** (Game: guessing birthdays) Listing 3.3, GuessBirthday.java, gives a program for guessing a birthday. Create an applet for guessing birthdays as shown in Figure 18.28. The applet prompts the user to check whether the date is in any of the five sets. The date is displayed in the text field upon clicking the Guess Birthday button.

18.25*** (Game: Sudoku) §7.7 introduced the Sudoku problem. Write a program that lets the user enter the input from the text fields in an applet, as shown in Figure 18.1. Clicking the Solve button displays the result.

Programming Exercises 647

vertically; when the light turns green, the traffic flows horizontally. The light changes automatically every one minute. Before the light changes to red from green, it first changes to yellow for a brief five seconds.

18.28** (Geometry: two circles intersect?) The Circle2D class was defined in Exercise 10.11. Write an applet that enables the user to specify the location and size of the circles and displays whether the two circles intersect, as shown in Figure 18.31(a).

FIGURE 18.31 Check whether two circles, two rectangles, and two triangles are overlapping.

18.29** (Geometry: two rectangles intersect?) The MyRectangle2D class was defined in Exercise 10.12. Write an applet that enables the user to specify the location and size of the rectangles and displays whether the two rectangles intersect, as shown in Figure 18.31(b).

18.30** (Geometry: two triangles intersect?) The Triangle2D class was defined in Exercise 10.13. Write an applet that enables the user to specify the location of the two triangles and displays whether the two triangles intersect, as shown in Figure 18.31(c).

18.31***(Game: bean-machine animation) Write an applet that animates a bean machine introduced in Exercise 16.22. The applet lets you set the number of slots, as shown in Figure 18.32. Click Start to start or restart the animation and click Stop to stop.

FIGURE 18.32 (a)–(c) The applet controls a bean-machine animation. (d) The applet counts down the time.

18.32* (Count-down alarm) Write an applet that allows the user to enter time in minutes in the text field and press the Enter key to count down the minutes, as shown in Figure 18.32(d). The remaining minutes are redisplayed every

648 Chapter 18 Applets and Multimedia

one minute. When the minutes are expired, the program starts to play music continuously.

18.33** (Pattern recognition: consecutive four equal numbers) Write an applet for Exercise 7.19, as shown in Figure 18.33 (a–b). Let the user enter the numbers in the text fields in a grid of 6 rows and 7 columns. The user can click the Solve button to highlight a sequence of four equal numbers, if it exists.

FIGURE 18.33 (a)–(b) Clicking the Solve button to highlight the four consecutive numbers in a row, a column, or a diagonal. (c) The applet enables two players to play the connect-four game.

18.34***(Game: connect four) Exercise 7.20 enables two players to play the connectfour game on the console. Rewrite the program using an applet, as shown in Figure 18.33(c). The applet enables two players to place red and yellow discs in turn. To place a disk, the player needs to click on an available cell. An available cell is unoccupied and whose downward neighbor is occupied. The applet flashes the four winning cells if a player wins and reports no winners if all cells are occupied with no winners.

CHAPTER 19

BINARY I/O

Objectives

■To discover how I/O is processed in Java (§19.2).

■To distinguish between text I/O and binary I/O (§19.3).

■To read and write bytes using FileInputStream and FileOutputStream (§19.4.1).

■To filter data using base classes FilterInputStream/FilterOutputStream

(§19.4.2).

■To read and write primitive values and strings using

DataInputStream/DataOutputStream (§19.4.3).

■To store and restore objects using ObjectOutputStream and ObjectInputStream, and to understand how objects are serialized and what kind of objects can be

serialized (§19.6).

■To implement the Serializable interface to make objects serializable (§19.6.1).

■To serialize arrays (§19.6.2).

■To read and write files using the RandomAccessFile class (§19.7).