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If you have previously stored a favorite frequency in the storage location corresponding to that button, pressing the button (sending the message) will cause the radio station transmitting at that frequency to be heard through the radio's speakers.
If you have not previously stored a favorite frequency in the storage location corresponding to that button, you will probably only hear static. (That doesn't mean that the radio object failed to respond correctly to the message. It simply means that its response was based on bad data.)
Modifying the stored data
The human interface also makes it possible for you to store or modify those five or more frequency values. This is done in different ways for different radios. On my car radio, the procedure is:
When the radio beeps, I know that the new frequency value has been stored in a storage location that corresponds to that particular button.
Please change your state
What I have done here is to send a message to the radio object asking it to change its state. The beep that I hear could be interpreted as the radio object returning a value back to me indicating that the mission has been accomplished. (Alternately, we might say that the radio object sent a message back to me.)
We say that an object has changed its state when one or more data values stored in the object have been modified.
We also say that when an object responds to a message, it will usually perform an action, change its state, return a value, or some combination of the above.
Please perform an action
Following this, when I press that button (send a message) , the radio object will be automatically tuned to that frequency.
While the ability to cause your car radio to remember your list of favorite stations may seem like a miracle of modern digital electronics, the truth is that radios had this capability long before they contained digital electronics. My first car had a radio that accomplished this feat using strings, pulleys, and levers.
As I recall, in order to set the frequency for a button, I had to manually tune the radio to a station by turning a knob, pull one of the buttons out about a quarter of an inch, and then push it in again. From that point until I did the same thing again, whenever I pressed that button, some kind of a mechanical contraption caused a big rotary capacitor to turn just the right amount to tune for a particular radio station.
Also, I remember my grandfather having a table-model radio in the early 1940's that had radio buttons. He used them to select his favorite stations, as he surfed the airwaves.
(Interestingly, the term radio button has now become a part of programming jargon, signifying certain visual components used in graphical user interfaces.)
Enough of that, now back to my modern car radio
If I drive to Dallas and press a button that I have associated with a particular radio station in Austin, I will probably hear static. In that case,I may want to change the frequency value associated with that button. I can follow the same procedure described earlier to set the frequency value associated with that button to correspond to one of the radiostations in Dallas. (Again, I would be sending a message to the radio object asking it to change its state.)
Notification Switch
Would you like to follow the 'Object-oriented programming (oop) with java' conversation and receive update notifications?
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