String s = "2015-10-26"; 
Pattern p = Pattern.compile("(?<year>\\d{4})-(?<month>\\d{2})-(?<day>\\d{2})"); 
Matcher m = p.matcher(s); 
if (m.find()) { 
  System.out.println("year: " + m.group("year")); //年 
  System.out.println("month: " + m.group("month")); //月 
  System.out.println("day: " + m.group("day")); //日 
    
  System.out.println("year: " + m.group(1)); //第一组 
  System.out.println("month: " + m.group(2)); //第二组 
  System.out.println("day: " + m.group(3)); //第三组 
} 
 
System.out.println(s.replaceAll("(?<year>\\d{4})-(?<month>\\d{2})-(?<day>\\d{2})", "${day}-${month}-${year}")); //将 年-月-日 形式的日期改为 日-月-年 形式 

year: 2015
month: 10
day: 26
year: 2015
month: 10
day: 26
26-10-2015