Java String类正则操作示例

public class RegExp
{
  public static void main(String[] args) throws Exception
  {
    if ("123".matches("\\d+"))
    {
      System.out.println("由数字组成！");
    } else
    {
      System.out.println("不是由数字组成！");
    }
  }
}

public class SubString
{
  public static void main(String[] args) throws Exception
  {
    String str = "a1b22c333d4444e55555f6666666g";
    String regex = "[0-9]+"; // 数字出现1次或多次
    //String regex = "\\d+"; // 数字出现1次或多次
    System.out.println(str.replaceAll(regex, ""));
  }
}

import java.util.*;
public class EmailValidation
{
  public static void main(String[] args) throws Exception
  {
    String str = null;
    String regex = "\\w+@\\w+.\\w+";
    Scanner reader = new Scanner(System.in);
    do
    {
      System.out.print("请输入一个有效的邮件地址：");
      str = reader.next();
      System.out.println(str);
    } while (!str.matches(regex));
    System.out.println("邮件地址有效！谢谢注册！");
    reader.close();
  }
}