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W002 Singleton With Required Object

Umple semantic warning reported when a singleton class has an association with a multiplicity lower bound of 1 at the other end of the association

The constructor of a singleton can't take any arguments. Therefore, it can't have a required link to another object, since this would have to be specified in the constructor. Any associations to other classes should therefore have multiplicity with lower bound of zero.

Note: Conceptually, this warning would also have been produced if the lower bound was something greater than 1 (e.g. 5). However, Umple treats a multiplicity specified with a lower bound > 1 as if the multiplicity lower bound was 0. The programmer is supposed to add the n elements immediately after construction. The API has a validity check method to verify this has been done.

Example

// This example generates the warning message
class X {
  singleton;
  0..1 -- 1 Y;
}

class Y {
}
      

Load the above code into UmpleOnline

Solution to The Above So the Message No Longer Appears

// The following shows how to avoid the warning
class X {
  singleton;
  0..1 -- 0..1 Y;
}

class Y {
}
      

Load the above code into UmpleOnline