Java 正则表达式 向前、向后匹配

//向后匹配

String a = "I paid $90 for 10 oranges, 12 pears and 8 apples. I saved $5 on ";

Pattern p = Pattern.compile("(?<=\\$)\\d+");

Matcher m = p.matcher(a);

while (m.find ())

{

String group = m.group ();

System.out.println (group);

}

向前匹配

a = "https://mail.huawei.com ";

p = Pattern.compile(".+(?=:)");

m = p.matcher(a);

while (m.find ())

{

String group = m.group ();

System.out.println (group);

}