A very simple ClockDisplay

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All the ClockDisplay example really does is returning a String like “13:45” from getTime() after either the time has been set to 13:45 by calling setTime() or after calling the timeTick() method the appropriate amount of times.

This can, of course, be implemented in a much simpler way. While this may be true for most of the small examples we use for programming and software engineering classes, I feel that the way the display is split into two NumberDisplays in combination with the timeTick / increment makes little sense and seems to be quite confusing for students. Also, see the general critique on the previous page.

Refactoring to a simple solution

The public interface are the public methods in ClockDisplay , NumberDisplay is an implementation detail.

The Interface of ClockDisplay consists of three methods, as can be seen in the BlueJ menu:

Here’s a much simpler and shorter implementation of this Interface:

Simple Version: Class Diagram

%%{
  init: {
    'theme': 'base',
    'themeVariables': {
      'primaryColor': '#f0cd91', 
      'primaryTextColor': '#000',
      'primaryBorderColor': '#000',
      'lineColor': '#F8B229',
      'secondaryColor': '#006100',
      'tertiaryColor': '#fff'
    }
  }
}%%
classDiagram
    class ClockDisplay

    ClockDisplay: -int ticks
    ClockDisplay: -String displayString
    ClockDisplay: void timeTick()
    ClockDisplay: void setTime(int hour, int minute)
    ClockDisplay: String getTime()
    
    

Simple Version: Creation

%%{
  init: {
    'theme': 'base',
    'themeVariables': {
      'primaryColor': '#f69e9d', 
      'primaryTextColor': '#000',
      'primaryBorderColor': '#000',
      'lineColor': '#F8B229',
      'secondaryColor': '#f4f4f4',
      'activationBorderColor': '#000',
      'tertiaryColor': '#fff'
    }
  }
}%%

sequenceDiagram
    actor YOU
    create Participant ClockDisplay
    YOU->>+ClockDisplay: new()
    ClockDisplay-->>-YOU:clockDisplay

Simple Version: setTime()

%%{
  init: {
    'theme': 'base',
    'themeVariables': {
      'primaryColor': '#f69e9d', 
      'primaryTextColor': '#000',
      'primaryBorderColor': '#000',
      'lineColor': '#F8B229',
      'secondaryColor': '#f4f4f4',
      'activationBorderColor': '#000',
      'tertiaryColor': '#fff'
    }
  }
}%%

sequenceDiagram
    actor YOU
    YOU->>+ClockDisplay: setTime(13,45)
    ClockDisplay->>+ClockDisplay:updateDisplay()
    deactivate ClockDisplay
    ClockDisplay-->>-YOU:void

Simple Version: timeTick()

%%{
  init: {
    'theme': 'base',
    'themeVariables': {
      'primaryColor': '#f69e9d', 
      'primaryTextColor': '#000',
      'primaryBorderColor': '#000',
      'lineColor': '#F8B229',
      'secondaryColor': '#f4f4f4',
      'activationBorderColor': '#000',
      'tertiaryColor': '#fff'
    }
  }
}%%
sequenceDiagram
    actor YOU
    participant ClockDisplay

    YOU->>+ClockDisplay: timeTick()
    
    ClockDisplay->>+ClockDisplay:updateDisplay()
    deactivate ClockDisplay

    ClockDisplay-->>-YOU:void

This example can no longer be used to show Object interaction. It only shows an object calling its own method (updateDisplay()) and how to use a modulo operator.