Java 正则表达式

import java.util.Calendar;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegularExpression {

    public static void main(String[] args) {

        String name = "今年是2013年吗？";
        String year = "";
        Pattern pa = Pattern.compile("[0-9]{4}"); //正则表达式（匹配4个数字）
        Matcher m = pa.matcher(name); //name是待匹配的字符串
        if (m.find()) {         //如果匹配得到
            year = m.group();  //符合正则表达式的字符串
        } else {
            Calendar calendar = Calendar.getInstance();
            year = "" + calendar.get(Calendar.YEAR);
        }
        System.out.println(year);
    }

}