checker/tests/index/Stopwatch.java

import java.text.DecimalFormat;
import org.checkerframework.checker.index.qual.IndexFor;

public final class Stopwatch {
  private static final DecimalFormat[] timeFormat = {
    new DecimalFormat("#.#"),
    new DecimalFormat("#.#"),
    new DecimalFormat("#.#"),
    new DecimalFormat("#.#"),
    new DecimalFormat("#.#"),
  };

  public DecimalFormat format(@IndexFor("Stopwatch.timeFormat") int digits) {
    return Stopwatch.timeFormat[digits];
  }
}