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More importantly, you will learn how to bring all of this knowledge together to demonstrate runtime polymorphism using sound.
This program requires access to the following classes:
You will find source code for all of these classes in Listing 5 through Listing 16 .
You are already familiar with some of these classes because they were used in earlier modules.
The driver class for this program is the class named MusicComposer08 . That is the only one of the twelve classes that I will discuss in detail. I willleave it as an exercise for the students at this point to study and understand the remaining eleven classes.
The purpose of this program is to demonstrate late binding and runtime polymorphism . This is accomplished by using an array of the abstract type AudioSignalGenerator02 populated with references to objects of the following eight classes :
Each of the classes listed above extends the abstract class named AudioSignalGenerator02 and overrides the inherited abstract method named getMelody .
After the array is populated, a random number generator is used to get a random index into the array. The getMelody method is called on the reference pointed to by the random index. This causes the sound created by that particular audioobject to be played or filed.
This is an example of late binding and runtime polymorphism because the compiler cannot possibly know the value of the random index when the programis compiled.
As in previous modules, the sound can be played immediately or can be saved in an audio file of type AU for playback later. You should be able to play the audio file with anystandard media player that can handle the AU file type.
The program also requires access to the following classes:
Listing 1 shows the beginning of the class named MusicComposer08 . The code in Listing 1 is essentially the same as code that I have explained in several previous modules. Therefore, no further discussion of the code in Listing 1 will be provided in this module.
| Listing 1 . Beginning of the class named MusicComposer08. |
|---|
import java.util.Random;
public class MusicComposer08{//Instantiate an object containing audio format parameters with predefined
// values. They may be modified by the signal generator at runtime. Values// allowed by Java SDK 1.4.1 are shown in comments in the class definition.
AudioFormatParameters01 audioParams = new AudioFormatParameters01();//A buffer to hold the audio data that will be played or filed.byte[] melody;//A place to store the incoming args array.
String[]args;
//-------------------------------------------------------------------------////Command-line parameter (only one parameter is needed)
//If "play", the sound will be played immediately. Otherwise, the string will// be used as a filename for an audio file of type AU. In the latter case,
// it must be a string that would be valid as a file name for the operating// system in use.
public static void main(String[]args){
//Instantiate a new object of this class.new MusicComposer08(args);
}//end main//-------------------------------------------------------------------------//public MusicComposer08(String[] args){//constructor//Save the args array.
this.args = args;//Create default args data if no args data is provided on the command line.if(args.length == 0){
this.args = new String[1];
this.args[0]= "play";//Play the melody immediately
}//end if |
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