Design of the Original

The #colon;ClockDisplay project is the first example for solving a problem using communicating objects. (in the Book “Objects First with Java: A Practical Introduction Using Bluej.” by David J Barnes and Michael Kölling)

Here’s a class diagram with the private fields and public methods (Constructors are omitted for clarity):

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

    class ClockDisplay{
      -NumberDisplay hours
      -NumberDisplay minutes
      -String displayString
      void timeTick()
      void setTime(int hour, int minute)
      String getTime()
      -void updateDisplay()
    }
    
    NumberDisplay: -int limit
    NumberDisplay: -int value
    NumberDisplay: int getValue()
    NumberDisplay: String getDisplayValue()
    NumberDisplay: void setValue(int)
    NumberDisplay: void increment()

Within the example the field displayString in ClockDisplay is used to simulate the digital display. It is updated after every change to the time by calling the private method updateDisplay after every change to the time. The two instances of NumberDisplay generate their part of the displayString in getDisplayValue. But they also hold their part of the model - the value for hours and minutes respectively.

The observable behavior of this example is returning a String like “13:45” from getTime() after either the time has been set to 13:45 by calling setTime() or by calling the tick() method the appropriate amount of times.

Original 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 #colon;ClockDisplay
    YOU->>+#colon;ClockDisplay: new ClockDisplay()
    create Participant hours#colon;NumberDisplay
  
    #colon;ClockDisplay->>+hours#colon;NumberDisplay:new NumberDisplay(24)
    hours#colon;NumberDisplay-->>-#colon;ClockDisplay:hours
    create Participant minutes#colon;NumberDisplay
    #colon;ClockDisplay->>+minutes#colon;NumberDisplay:new NumberDisplay(60)
    minutes#colon;NumberDisplay-->>-#colon;ClockDisplay:minutes
    #colon;ClockDisplay-->>-YOU:#colon;ClockDisplay

Original Version: setTime()

%%{
  init: {
    'theme': 'base',
    'themeVariables': {
      'primaryColor': '#f69e9d', 
      'primaryTextColor': '#000',
      'primaryBorderColor': '#000',
      'lineColor': '#F8B229',
      'secondaryColor': '#f4f4f4',
      'activationBorderColor': '#000',
      'tertiaryColor': '#fff'
    }
  }
}%%
sequenceDiagram
    actor YOU
    YOU->>+#colon;ClockDisplay: setTime(13,45)
    #colon;ClockDisplay->>+hours#colon;NumberDisplay:setValue(13)
    hours#colon;NumberDisplay-->>-#colon;ClockDisplay:void
    #colon;ClockDisplay->>+minutes#colon;NumberDisplay:setValue(45)
    minutes#colon;NumberDisplay-->>-#colon;ClockDisplay:void
    
    #colon;ClockDisplay->>+#colon;ClockDisplay:updateDisplay()
    #colon;ClockDisplay->>+hours#colon;NumberDisplay:getDisplayValue()
    hours#colon;NumberDisplay-->>-#colon;ClockDisplay:displayString
    #colon;ClockDisplay->>+minutes#colon;NumberDisplay:getDisplayValue()
    minutes#colon;NumberDisplay-->>-#colon;ClockDisplay:displayString
    
    deactivate #colon;ClockDisplay

    #colon;ClockDisplay-->>-YOU:void

Original Version: timeTick()

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

    participant #colon;ClockDisplay
    participant hours#colon;NumberDisplay
    participant minutes#colon;NumberDisplay

    YOU->>+#colon;ClockDisplay: timeTick()
    #colon;ClockDisplay->>+minutes#colon;NumberDisplay:increment()
    minutes#colon;NumberDisplay-->>-#colon;ClockDisplay:void

    #colon;ClockDisplay->>+minutes#colon;NumberDisplay:getValue()
    minutes#colon;NumberDisplay-->>-#colon;ClockDisplay:value

    alt [value == 0]

    #colon;ClockDisplay->>+hours#colon;NumberDisplay:increment()
    hours#colon;NumberDisplay-->>-#colon;ClockDisplay:void
    end
  

    #colon;ClockDisplay->>+#colon;ClockDisplay:updateDisplay()
    #colon;ClockDisplay->>+hours#colon;NumberDisplay:getDisplayValue()
    hours#colon;NumberDisplay-->>-#colon;ClockDisplay:displayString
    #colon;ClockDisplay->>+minutes#colon;NumberDisplay:getDisplayValue()
    minutes#colon;NumberDisplay-->>-#colon;ClockDisplay:displayString
    deactivate #colon;ClockDisplay

    #colon;ClockDisplay-->>-YOU:void

Original Version: getTime()

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

    YOU->>+#colon;ClockDisplay: getTime()
   
    #colon;ClockDisplay-->>-YOU:displayString