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📜 WAYPOINT LESSON

Edge cases by type

⭐⭐⭐ advanced⏳ 10 min read📍 Lesson 210 of 256

Each data type owns a canonical edge set: run the empty and single-element cases before the example.

Edge cases by type. Each data type owns a canonical edge set:

  • String: empty, single char, all-same, alternating. Adjacent scans start at i = 1 and compare charAt(i) to charAt(i - 1).
  • Array: empty, one element, all-equal (tie-break territory), negatives (initialization must survive: use arr[0] or MIN_VALUE, never 0).
  • ArrayList: empty, removals while scanning (iterate backward or build anew), .equals for objects — == on Integer beyond the small cache is a latent bug.
  • Recursion: zero, one digit/element, and the shape of the smallest input that still recurses once.

The habit that earns the edge-case rubric line: after coding, RUN your plan against the empty input and the single element before the example in the prompt. The example is seductive; edges are where the hidden tests live.