10-7 ?を使う可変長戻り読み

正規表現パズル

Javaの正規表現では、?を使う可変長戻り読みが使えます。

JavaのStringクラス
Javaの正規表現のドキュメント

ソース

import java.util.regex.*;

public class sample10_7{
    private static final String PATTERN = "(?<=Xa?b?c?)Y.*$";
    public static void main(String argv[]){
        String[] strArray = new String[7+1];
        strArray[1] = "XX111";
        strArray[2] = "XabcY222";
        strArray[3] = "XabY333";
        strArray[4] = "XaY444";
        strArray[5] = "XacY555";
        strArray[6] = "XccY666";
        strArray[7] = "XY777";

        System.out.println("Pattern " + PATTERN);
        Pattern p = Pattern.compile(PATTERN);

        for (int i=1;i<=7;i++){
            String willOut = "Line" + Integer.toString(i) + " " + strArray[i] + " ";
            Matcher m = p.matcher(strArray[i]);

            if (m.find()) willOut += "matchs " + m.group();
            else willOut += "no match";

            System.out.println(willOut);
        }
    }
}

実行結果

Pattern (?<=Xa?b?c?)Y.*$
Line1 XX111 no match
Line2 XabcY222 matchs Y222
Line3 XabY333 matchs Y333
Line4 XaY444 matchs Y444
Line5 XacY555 matchs Y555
Line6 XccY666 no match
Line7 XY777 matchs Y777