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Exceptions in the Contract

/**

   . . .

   @throws IllegalArgumentException if queue is empty

*/

public Message removeFirst()

{

   if (count == 0)

      throw new IllegalArgumentException();

   Message r = elements[head];

   . . .

}

• Exception throw part of the contract
• Caller can rely on behavior
• Exception throw not result of precondition violation
• This method has no precondition
  

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