Object interaction - Objects First with Java: A Practical Introduction Using BlueJ - page 75

Code 3.4
continued
Implementation of the
ClockDisplay
class

public void timeTick()
{

minutes.increment();
if (minutes.getValue() == 0) { // it just rolled over!
hours.increment();

}
updateDisplay();

}
/**
* Set the time of the display to the specified hour and
* minute.
*/
public void setTime( int hour, int minute)
{
hours.setValue(hour);
minutes.setValue(minute);
updateDisplay();
}
/**
* Return the current time of this display in the format
* HH:MM.
*/
public String getTime()
{

return displayString;

}
/**
* Update the internal string that represents the
* display.
*/
private void updateDisplay()
{

displayString = hours.getDisplayValue() + ":" +
minutes.getDisplayValue();

}
}

In this project, we use the field displayString to simulate the actual display device of the
clock (as you could see in Exercise 3.5). Were this software to run in a real clock, we would
present the output on the real clock display instead. So this string serves as our software simula-
tion for the clock's output device. 1

1 The topic projects folder also includes a version of this project with a simple graphical user interface
(GUI), named clock-display-with-GUI . The curious reader may like to experiment with this project;
however, it will not be discussed in this topic.