Umple Keys for Equality and Hashing
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Keys for Equality and Hashing
In any class you can specify a set of attributes and associations as keys. The associations must have a multiplicity of 1 at the other end. This allows Umple to generate code that defines what objects of the class are equal (they have the same values for the key).
Umple will also generate a hashCode method in any class that has a defined key. This helps when looking up an object in a set.
Place the comma-separated list of key elements in curly brackets, after the word key. If you have multiple key statements, a warning is generated.
Example
class Sport {
name;
description;
code;
key { code }
}
class League {
name;
id;
geographicalArea;
* -- 1 Sport;
Date seasonStart;
Date seasonEnd;
key { id }
}
class Team {
name;
* -- 1 League;
}
class Player {
name;
Integer id;
key { id }
}
class PlayerOnTeam {
Integer year;
* -- 1 Player;
* -- 1 Team;
key { year, player, team }
}
Load the above code into UmpleOnline
Syntax
softwarePattern- : [[isA]] | [[singleton]] | [[immutable]] | [[keyDefinition]] | [[codeInjection]]
// For equality and hashing KeysforEqualityandHashing
keyDefinition- : [[defaultKey]] | [[key]]
// Keys are used to define quality and hash codes, plus Sql keys.
// See user manual page KeysforEqualityandHashing
defaultKey : key { }
key : key { [keyId] ( , [keyId] )* }