“Greedy” 和 “Reluctant” 正则表达式量词有什么区别？

来自Pattern http://java.sun.com/javase/6/docs/api/java/util/regex/Pattern.htmljava文档：

Greedy quantifiers:
X?      X, once or not at all  
X*      X, zero or more times  
X+      X, one or more times  
X{n}    X, exactly n times  
X{n,}   X, at least n times  
X{n,m}  X, at least n but not more than m times

Reluctant quantifiers:
X??     X, once or not at all  
X*?     X, zero or more times  
X+?     X, one or more times  
X{n}?   X, exactly n times  
X{n,}?  X, at least n times  
X{n,m}? X, at least n but not more than m times
  

他们所做的事情的描述是相同的......那么，有什么区别呢？

我真的很感激一些例子。

我正在使用 Java 进行编码，但我听说这个概念对于大多数现代正则表达式实现来说是相同的。

贪婪的运算符总是尝试“获取”尽可能多的输入，而不情愿的量词将匹配尽可能少的输入，但仍然会创建匹配。

Example:

"The red fox jumped over the red fence"
/(.*)red/ => \1 = "The red fox jumped over the "
/(.*?)red/ => \1 = "The "

"aaa"
/a?a*/ => \1 = "a", \2 = "aa"
/a??a*/ => \1 = "", \2 = "aaa"

"Mr. Doe, John"
/^(?:Mrs?.)?.*\b(.*)$/ => \1 = "John"
/^(?:Mrs?.)?.*?\b(.*)$/ => \1 = "Doe, John"