One fall afternoon, Java master Bawan heard that the monk Landhwa had been struggling with a straightforward data-extraction program. Intrigued, Bawan visited the monk, who was slouching low in his chair.

“The program runs out of memory,” yawned Landhwa, who had no patience for such investigations. “True, it processes many large files, but it does so one at a time, and retains only the smallest snippet from each.”

“Show me,” said Bawan.

The monk sighed, pointing to the screen. “To process a file, I read its lines into a List of Strings. This I search to find the section of interest: a few short lines at most. I extract that via subList, and store it in this static Map. The code could not be simpler.”

Bawan nodded. “Meet me at midnight on the river dock, down in the village,” he said. “I know who can help us, and the journey is not a long one.”

That night Landhwa descended with a lantern to the foggy banks. Spying a twinkling light on the water, he followed the boardwalk past dozens of small watercraft to find small master Bawan seated in the last rowboat at the end of the pier. The master gestured to the oars.

“Upstream,” said Bawan.

Landhwa pulled at the oars alone, while the master sat silently in the stern with arms folded. Each stroke against the current was a painful struggle, yet somehow the little craft inched its way forward through the fog. Hours passed. Just when Landhwa was on the verge of collapse, Bawan ordered him to dock at an ramshackle pier far from the last village they’d passed. The master looped a coil of rope around one of the pilings to anchor them.

“We wait,” said Bawan.

Dawn came, scattering the night fog, but still no one approached from the banks. When he happened to glance downriver, Landhwa discovered that their rowboat had been towing another boat by an underwater line many yards long. The lifting fog revealed another boat beyond that, and then another and another; and though the tenth passed out of sight beyond a bend in the river, Landhwa was certain that he had unwittingly towed every boat in the river dock behind them that night.