TWO_BYTE_ROUNDTRIPPABLE_CHARACTERS * TWO_BYTE_ROUNDTRIPPABLE_CHARACTERS
          +
          // Permutations of one and two byte characters
          3
              * TWO_BYTE_ROUNDTRIPPABLE_CHARACTERS
              * ONE_BYTE_ROUNDTRIPPABLE_CHARACTERS
              * ONE_BYTE_ROUNDTRIPPABLE_CHARACTERS
          +
          // Four byte characters
          FOUR_BYTE_ROUNDTRIPPABLE_CHARACTERS;

  /**
   * Substitute: A character that may be substituted for a character which is determined to be
   * invalid or in error.
   *
   * @since 8.0
   */
  public static final byte SUB = 26;

  /**
   * Escape: A control character intended to provide code extension (supplementary characters) in
   * general information interchange. The Escape character itself is a prefix affecting the

          TWO_BYTE_ROUNDTRIPPABLE_CHARACTERS * TWO_BYTE_ROUNDTRIPPABLE_CHARACTERS
          +
          // Permutations of one and two byte characters
          3
              * TWO_BYTE_ROUNDTRIPPABLE_CHARACTERS
              * ONE_BYTE_ROUNDTRIPPABLE_CHARACTERS
              * ONE_BYTE_ROUNDTRIPPABLE_CHARACTERS
          +
          // Four byte characters
          FOUR_BYTE_ROUNDTRIPPABLE_CHARACTERS;

   *
   * @param seq the sequence of characters from which to decode the code point
   * @param index the index of the first character to decode
   * @param end the index beyond the last valid character to decode
   * @return the Unicode code point for the given index or the negated value of the trailing high
   *     surrogate character at the end of the sequence
   */
  protected static int codePointAt(CharSequence seq, int index, int end) {

    return total;
  }

  /**
   * Discards {@code n} characters of data from the reader. This method will block until the full
   * amount has been skipped. Does not close the reader.
   *
   * @param reader the reader to read from
   * @param n the number of characters to skip
   * @throws EOFException if this stream reaches the end before skipping all the characters
   * @throws IOException if an I/O error occurs
   */

  /**
   * Substitute: A character that may be substituted for a character which is determined to be
   * invalid or in error.
   *
   * @since 8.0
   */
  public static final byte SUB = 26;

  /**
   * Escape: A control character intended to provide code extension (supplementary characters) in
   * general information interchange. The Escape character itself is a prefix affecting the

   *     separator
   */
  public abstract BaseEncoding withPadChar(char padChar);

  /**
   * Returns an encoding that behaves equivalently to this encoding, but adds a separator string
   * after every {@code n} characters. Any occurrences of any characters that occur in the separator
   * are skipped over in decoding.
   *

    assertFailsToDecode(base16(), "\n\n", "Unrecognized character: 0xa");
    assertFailsToDecode(base16(), "EFGH", "Unrecognized character: G");
    // Valid base16 strings always have an even length.
    assertFailsToDecode(base16(), "A", "Invalid input length 1");
    assertFailsToDecode(base16(), "ABC");
    // These have a combination of invalid length and unrecognized characters.

    private static final long serialVersionUID = 0;
  }

  /**
   * Creates a {@code HashCode} from a hexadecimal ({@code base 16}) encoded string. The string must
   * be at least 2 characters long, and contain only valid, lower-cased hexadecimal characters.
   *
   * <p>This method accepts the exact format generated by {@link #toString}. If you require more

import java.util.List;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * A readable source of characters, such as a text file. Unlike a {@link Reader}, a {@code
 * CharSource} is not an open, stateful stream of characters that can be read and closed. Instead,
 * it is an immutable <i>supplier</i> of {@code Reader} instances.
 *
 * <p>{@code CharSource} provides two kinds of methods:
 *