Many thanks to Hanzík for the Czech translations!

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extremely geeky  extremely geeky

Case 64

Three Beggars

Java master Kaimu led three senior monks to the Hall Of Endless Cubicles. There he gathered three novices in his charge.

“A utility method is needed which takes an employee ID and from it constructs a particular URL,” said Kaimu. “The logic is not trivial, but ultimately it reduces to text substitution.”

Kaimu gestured to the first old monk. “This one works on the persistence tier, where all database keys are large integers. Understandably, he wishes the method to take a Long.”

Kaimu gestured to the second old monk. “This one works on the business tier, which employs strong typing. He wishes the method to take an EmployeeID object.”

Kaimu gestured to the third old monk. “This one works on the web tier, where all data is manipulated as text. He wishes the method to take a String.”

The master then bowed to the three monks, and bade the novices offer their solutions.

- - -

The first novice stood. “The method should take a String, for that representation will be most useful within the method itself. As for the monks who prefer Long or EmployeeID, they can easily invoke toString on those objects and feed the result into the method.”

Said Kaimu: “When the beggar squatting in the dirt asks you for coins, you may well demand that he lift up his bowl to meet you. But what of the man with no elbows?”

Before the first novice could answer, the second stood. “The apparent simplicity of invoking toString is hampered by the caller’s need to check for null first. So the method should take an Object, which can hold any of the three types. The method itself can check for null, and invoke toString only if it is safe to do so. Thus, nothing is required of the caller.”

Said Kaimu: “Knowing the armless beggar can only accept what is placed on his tongue, you charitably go everywhere with rice in your pockets. Yet you toss your grains into anyone’s mouth. How glad you make the rats and magpies!”

The third novice stood. “Three monks, three novices. Why not three methods, each taking a different type? EmployeeID, Long, and String. The first and second can delegate to the third, and each can check for null.”

Said Kaimu: “Not a scrap for the rats in your village, but how fat the beggars must be! Yet if a method takes four parameters, will you write it eighty-one different ways? You may waste so much time pleasing everyone that you please no one.”

Kaimu then bade the senior monks depart, to let the novices determine for themselves the best way to satisfy all concerns.

- - -

The first old monk whispered as they went: “What approach will be decided upon, do you think?”

The second old monk replied: “If they are anything like us, it will be the one championed by the novice who shouts the loudest.”

The third old monk nodded. “Doubtless, some of us will find fault with the solution, yet begrudgingly we will abide by it, and the world will continue to turn. But so it goes: we are all of us beggars at each others’ feet.”