1.  一般来说，正则表达式就是以某种方式来描述字符串。

  在其他语言中，\\表示“我想要在正则表达式中插入一个普通的（字面上的）反斜线，请不要给它任何特殊的意义。”而在Java中，\\的意思是“我要插入一个正则表达式的反斜线，所以其后的字符具有特殊的意义。”例如，如果你想表示一位数字，那么正则表达式应该是\\d。如果你想插入一个普通的反斜线，则应该这样\\\\。不过换行和制表符之类的东西只需使用单反斜线：\n\t。

  ？表示可能有某个字符。如-？表示可能有一个负号在前面。

  +表示一个或多个之前的表达式。

2.  String类自带正则表达式工具：

  1）matches , 检查string是否匹配正则表达式

"-1234".matches("-?\\d+"); //true

"you must do it".split("\\W+");//you, must, do, it

  3) replaceFirst ，replaceAll ， 替换

"you found it".replaceFirst("f\\w+","located"); //"you located it"
"you found it".replaceAll("f\\w+","located"); //"you located it"

• Construct	Matches
  Characters
  x	The character x
  \\	The backslash character
  \0n	The character with octal value 0n (0 <= n <= 7)
  \0nn	The character with octal value 0nn (0 <= n <= 7)
  \0mnn	The character with octal value 0mnn (0 <= m <= 3, 0 <= n <= 7)
  \xhh	The character with hexadecimal value 0xhh
  \uhhhh	The character with hexadecimal value 0xhhhh
  \x{h...h}	The character with hexadecimal value 0xh...h (Character.MIN_CODE_POINT  <= 0xh...h <= Character.MAX_CODE_POINT)
  \t	The tab character (‘\u0009‘)
  \n	The newline (line feed) character (‘\u000A‘)
  \r	The carriage-return character (‘\u000D‘)
  \f	The form-feed character (‘\u000C‘)
  \a	The alert (bell) character (‘\u0007‘)
  \e	The escape character (‘\u001B‘)
  \cx	The control character corresponding to x
  Character classes
  [abc]	a, b, or c (simple class)
  [^abc]	Any character except a, b, or c (negation)
  [a-zA-Z]	a through z or A throughZ, inclusive (range)
  [a-d[m-p]]	a through d, or m throughp:[a-dm-p] (union)
  [a-z&&[def]]	d, e, or f (intersection)
  [a-z&&[^bc]]	a through z, except for b andc:[ad-z] (subtraction)
  [a-z&&[^m-p]]	a through z, and not m throughp:[a-lq-z](subtraction)
  Predefined character classes
  .	Any character (may or may not match line terminators)
  \d	A digit: [0-9]
  \D	A non-digit: [^0-9]
  \h	A horizontal whitespace character: [ \t\xA0\u1680\u180e\u2000-\u200a\u202f\u205f\u3000]
  \H	A non-horizontal whitespace character: [^\h]
  \s	A whitespace character: [ \t\n\x0B\f\r]
  \S	A non-whitespace character: [^\s]
  \v	A vertical whitespace character: [\n\x0B\f\r\x85\u2028\u2029]
  \V	A non-vertical whitespace character: [^\v]
  \w	A word character: [a-zA-Z_0-9]
  \W	A non-word character: [^\w]

interface CharSequence {
    charAt(int i);
    length();
    subSequence(int start, int end);
    toString();
}

Pattern p=Pattern.compile("abc+");
Matcher m=p.matcher("abcabcac");
while(m.find){
    println("Match \""+m.group()+"\" at positions "+m.start()+"-"+(m.end()-1));
    //Match "abc" at positions 0-2
    //Match "abc" at positions 3-5
}