Umple 
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Preconditions
You can specify basic preconditions in methods as shown below. Like other constraints, they are specified in square brackets. Precondition appears as the first lines of a method and must start with 'pre:'. A precondition can refer to one or more attributes or method arguments. If a precondition is not satisfied when the method is run an exception will be thrown; in Java a RuntimeException is used.
Example
class PotentialVoter {
Integer age;
int vote(int candidate) {
[pre: age >= 18]
[pre: candidate > 0]
// rest of stuff that we do not interpret
return 0;
}
}
Load the above code into UmpleOnline
Syntax
// Constraints in Umple.
// This is currently under development. Constraint capability is being
// developed in agile increments. The first step, described below,
// allows limiting the values of attributes. Code generation is not currently enabled.
// Constraints may appear in classes (including association classes)
// as well as in states.
precondition : [ [name]? pre : [[constraint]] ]
//queuedMethodDeclaration- : queued [[methodDeclarator]] [[methodThrowsExceptions]]? [[methodBody]]
methodBody- :
( [[codeLangs]] {
( [[precondition]]
| [[postcondition]]
| [[assertion]]|[[testCase]]
)* [**code] }
)+