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A simple Java program

In order to help you to get started on the right foot, and in support of future discussions, it will be advantageous to provide and discuss a simple Java program in this module.

The car radio example

Listing 9 , near the end of this module, shows the code for a simple Java application that simulates the manufacture and the use of a car radio.

Explain in fragments

In order to help you to focus specifically on important sections of code, I will explain the behavior of this program in fragments.

Top-level classes

This program contains two top-level class definitions. (Java also supports inner classes in addition to top-level classes. Inner classes will be explained in detail in subsequent modules in this series.)

The class named Radio01

The definition of a class named Radio01 , is shown in its entirety in Listing 1 . The other class named Radio will be discussed later.

Listing 1 . The class named Radio01.
public class Radio01{ public static void main(String[] args){Radio myObjRef = new Radio(); myObjRef.setStationNumber(3,93.5);myObjRef.playStation(3); }//end main}//end class Radio01

The class named Radio01 consists simply of the main method. The main method of a Java application is executed by the Java Virtual Machine when the application is run. Thus, it is the driver for the entire application.

The driver class

The code in Listing 1 simulates the manufacturer of the radio and the use of the radio by the end user. Without getting into a lot of detail regarding Java syntax, I will further subdivide and discuss this code in the following listings.

Constructing a Radio object

As discussed in an earlier module, the code in Listing 2 applies the new operator to the constructor for the Radio class, causing a new object to be created according to the plans specified in the class named Radio .

Listing 2 . Constructing a Radio object.
Radio myObjRef = new Radio();

Saving a reference to the Radio object

Also as discussed in an earlier module, the code in Listing 2 declares a reference variable of type Radio and stores the new object's reference in that variable.

Programming the radio buttons

The code in Listing 3 is new to this discussion. This statement simulates the process of associating a particular radio station with a particular button - programming a button on the radio.

As I explained in an earlier module, this is accomplished for my car radio by manually tuning the radio to a desired station and then holding the radio button down until it beeps. You have probably done something similar to this to the radio in your family'scar.

Listing 3 . Programming the radio buttons.
myObjRef.setStationNumber(3, 93.5);

The statement in Listing 3 accomplishes the association of a simulated button to a simulated radio station by calling the method named setStationNumber on the reference to the Radio object. (Recall that this sends a message to the object asking it to change its state.)

The parameters passed to the method cause radio button number 3 to be associated with the frequency 93.5 MHz. (The value 93.5 is stored in the variable that represents button number 3.)

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Source:  OpenStax, Accessible objected-oriented programming concepts for blind students using java. OpenStax CNX. Sep 01, 2014 Download for free at https://legacy.cnx.org/content/col11349/1.17
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