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package java.util.regex;

/**
 * The result of a match operation.
 *
 * <p>This interface contains query methods used to determine the
 * results of a match against a regular expression. The match boundaries,
 * groups and group boundaries can be seen but not modified through
 * a {@code MatchResult}.
 *
 * @author  Michael McCloskey
 * @see Matcher
 * @since 1.5
 */
public interface MatchResult {

    /**
     * Returns the start index of the match.
     *
     * @return  The index of the first character matched
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     */
    public int start();

    /**
     * Returns the start index of the subsequence captured by the given group
     * during this match.
     *
     * <p> <a href="Pattern.html#cg">Capturing groups</a> are indexed from left
     * to right, starting at one.  Group zero denotes the entire pattern, so
     * the expression <i>m.</i>{@code start(0)} is equivalent to
     * <i>m.</i>{@code start()}.  </p>
     *
     * @param  group
     *         The index of a capturing group in this matcher's pattern
     *
     * @return  The index of the first character captured by the group,
     *          or {@code -1} if the match was successful but the group
     *          itself did not match anything
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     *
     * @throws  IndexOutOfBoundsException
     *          If there is no capturing group in the pattern
     *          with the given index
     */
    public int start(int group);

    /**
     * Returns the offset after the last character matched.
     *
     * @return  The offset after the last character matched
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     */
    public int end();

    /**
     * Returns the offset after the last character of the subsequence
     * captured by the given group during this match.
     *
     * <p> <a href="Pattern.html#cg">Capturing groups</a> are indexed from left
     * to right, starting at one.  Group zero denotes the entire pattern, so
     * the expression <i>m.</i>{@code end(0)} is equivalent to
     * <i>m.</i>{@code end()}.  </p>
     *
     * @param  group
     *         The index of a capturing group in this matcher's pattern
     *
     * @return  The offset after the last character captured by the group,
     *          or {@code -1} if the match was successful
     *          but the group itself did not match anything
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     *
     * @throws  IndexOutOfBoundsException
     *          If there is no capturing group in the pattern
     *          with the given index
     */
    public int end(int group);

    /**
     * Returns the input subsequence matched by the previous match.
     *
     * <p> For a matcher <i>m</i> with input sequence <i>s</i>,
     * the expressions <i>m.</i>{@code group()} and
     * <i>s.</i>{@code substring(}<i>m.</i>{@code start(),}&nbsp;<i>m.</i>{@code end())}
     * are equivalent.  </p>
     *
     * <p> Note that some patterns, for example {@code a*}, match the empty
     * string.  This method will return the empty string when the pattern
     * successfully matches the empty string in the input.  </p>
     *
     * @return The (possibly empty) subsequence matched by the previous match,
     *         in string form
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     */
    public String group();

    /**
     * Returns the input subsequence captured by the given group during the
     * previous match operation.
     *
     * <p> For a matcher <i>m</i>, input sequence <i>s</i>, and group index
     * <i>g</i>, the expressions <i>m.</i>{@code group(}<i>g</i>{@code )} and
     * <i>s.</i>{@code substring(}<i>m.</i>{@code start(}<i>g</i>{@code
     * ),}&nbsp;<i>m.</i>{@code end(}<i>g</i>{@code ))}
     * are equivalent.  </p>
     *
     * <p> <a href="Pattern.html#cg">Capturing groups</a> are indexed from left
     * to right, starting at one.  Group zero denotes the entire pattern, so
     * the expression {@code m.group(0)} is equivalent to {@code m.group()}.
     * </p>
     *
     * <p> If the match was successful but the group specified failed to match
     * any part of the input sequence, then {@code null} is returned. Note
     * that some groups, for example {@code (a*)}, match the empty string.
     * This method will return the empty string when such a group successfully
     * matches the empty string in the input.  </p>
     *
     * @param  group
     *         The index of a capturing group in this matcher's pattern
     *
     * @return  The (possibly empty) subsequence captured by the group
     *          during the previous match, or {@code null} if the group
     *          failed to match part of the input
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     *
     * @throws  IndexOutOfBoundsException
     *          If there is no capturing group in the pattern
     *          with the given index
     */
    public String group(int group);

    /**
     * Returns the number of capturing groups in this match result's pattern.
     *
     * <p> Group zero denotes the entire pattern by convention. It is not
     * included in this count.
     *
     * <p> Any non-negative integer smaller than or equal to the value
     * returned by this method is guaranteed to be a valid group index for
     * this matcher.  </p>
     *
     * @return The number of capturing groups in this matcher's pattern
     */
    public int groupCount();

}