Pattern Greedy, Reluctant, and Possessive 扫盲

原文是 http://java.sun.com/docs/books/tutorial/essential/regex/quant.html

有时候感慨到底java人有多少看过了tutorial

Greedy, Reluctant, and Possessive

input string xfooxxxxxxfoo.

    
    Enter your regex: .*foo  // greedy quantifier
    Enter input string to search: xfooxxxxxxfoo
    I found the text "xfooxxxxxxfoo" starting at index 0 and ending at index 13.

Greedy 其实是整个字符串开始匹配，然后慢慢的backs off，这样就能得到最大匹配串
(backs off的行为到底是怎么样的我没有研究)


    Enter your regex: .*?foo  // reluctant quantifier
    Enter input string to search: xfooxxxxxxfoo
    I found the text "xfoo" starting at index 0 and ending at index 4.
    I found the text "xxxxxxfoo" starting at index 4 and ending at index 13.

reluctant 是从字符串的最开始开始匹配，慢慢的增加，所以匹配到的是最小字串


    Enter your regex: .*+foo // possessive quantifier
    Enter input string to search: xfooxxxxxxfoo
    No match found.

possessive 是greeedy + no backs off，相当于整个字符串都塞进来看，结果.*就匹配了所有串，foo没有匹配到，所有就no match found

最后推荐一下 pattern 工具，这个工具的tutorial也很不错
http://www.regular-expressions.info/tutorial.html