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Case 30

Cups

Java master Bawan said: “The beggar in the marketplace owns nothing but empty cups. Fill all but one with tea and he will praise you; yet spill a drop into the last and he must instantly die of thirst. Explain.”

No monk could answer Bawan’s question. The teacher retired to his chambers.

That evening four students came to his door, seeking help with a truculent program. Its log files were overflowing with ArrayIndexOutOfBounds exceptions which the students insisted were impossible: the array in question was declared to hold a thousand elements, and the index—a one-byte integer—could never exceed 255 by definition.

Master Bawan pointed to an object in the corner. “What is that?” he asked of each student.

“A broom,” said each in turn.

Bawan then grabbed the broom and swung it wide over the heads of the students. Pictures were swept off the walls and sent spinning to the floor. Vases and cups came crashing down from their shelves. Paper screens tore. Dust fell from the rafters.

“Not a broom!” shouted Master Bawan, still swinging like a madman. “Not a broom!”

Qi’s Commentary

Each of the beggar’s cups is alike in every way to the one beside it, yet each also holds twice as much as the cup to its right. Now quickly say what it is.

Qi’s Poem

In the hand of a beggar, the staff engenders pity.
In the hand of a master, fear.
These qualities reside nowhere in the staff:
only in the where of it.

Topics...  overflow, integers, bits