// The highest index we've seen so far.
  private int max = -1;

  /** Construct a new sparse array builder. */
  public CharEscaperBuilder() {
    this.map = new HashMap<>();
  }

  /** Add a new mapping from an index to an object to the escaping. */
  @CanIgnoreReturnValue
  public CharEscaperBuilder addEscape(char c, String r) {
    map.put(c, checkNotNull(r));
    if (c > max) {
      max = c;
    }
    return this;

import org.jspecify.annotations.NullUnmarked;

@NullUnmarked
public class CharEscaperBuilderTest extends TestCase {

  public void testAddEscapes() {
    char[] cs = {'a', 'b', 'c'};
    CharEscaperBuilder builder = new CharEscaperBuilder().addEscapes(cs, "Z");
    Escaper escaper = builder.toEscaper();
    assertThat(escaper.escape("abcdef")).isEqualTo("ZZZdef");
  }

   * called by the {@link #escape(String)} method when it discovers that escaping is required. It is
   * protected to allow subclasses to override the fastpath escaping function to inline their
   * escaping test. See {@link CharEscaperBuilder} for an example usage.
   *
   * @param s the literal string to be escaped
   * @param index the index to start escaping from
   * @return the escaped form of {@code string}

   * called by the {@link #escape(String)} method when it discovers that escaping is required. It is
   * protected to allow subclasses to override the fastpath escaping function to inline their
   * escaping test. See {@link CharEscaperBuilder} for an example usage.
   *
   * <p>This method is not reentrant and may only be invoked by the top level {@link
   * #escape(String)} method.
   *
   * @param s the literal string to be escaped