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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. In fact, the radio in the first car that I owned many years ago is the firstprogrammable device of any complexity that I can remember.
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.)
Jargon
As you can see from the above discussion, the world of OOP is awash with jargon, and the ability to translate the jargon is essential to an understanding of the published material on OOP. Therefore, as we progress through this series ofmodules, I will introduce you to some of that jargon and try to help you understand the meaning of the jargon.
Persistence
The ability of your car radio to remember your list of favorite stations is often referred to as persistence. An object that has the ability to store and remember values is often said to have persistence.
State
It is often said that the state of an object at a particular point in time is determined by the values stored in the object. In our analogy, even if we own identical radios, unless the two of us have the same list of favorite radio stations, associated with the same combination of buttons, the state of your radio object at any particular point in time will be different from the state of my radio object.
Notification Switch
Would you like to follow the 'Accessible objected-oriented programming concepts for blind students using java' conversation and receive update notifications?
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