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Unique Attributes

Attributes in Umple can be unique. Applying the unique keyword to an attribute ensures that each instance of the class in the currently running program has a unique value for that attribute.

In the first example, each player has a unique ranking. The ranking of a player can change but two players cannot have the same ranking.

The autounique keyword can be used to automatically assign a unique Integer to every new instance created (example 2).

Certain runtime errors can occur if attempts are made to violate uniqueness.

Example 1

// Every player has a ranking.
// Rankings can be modified,
// but two different players 
// can not have the same ranking.

class Player
{
  unique Integer ranking;
}
      

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Example 2

// Unique registration numbers (Integer)
// are automatically assigned to every
// new registration created

class Registration
{
	autounique registrationNumber;
}
      

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