正则表达式初步
1 为什么用正则表达式？
String已经有了这个 String s.matchers(reg);和String s.replaceall（reg，“”）
使用pattern和matcher两个类的原因在于上面的字符串处理能力有限，丰富了其它的很多的方法，提高处理的能力。其次是提高程序代码执行的效率，先把pattern编译。
2 正则表达式基础
基本的正则表达式的:
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Test {
public static void main(String[] args) {
//简单认识正则表达式的概念
/*
p("abc".matches("..."));
p("a8729a".replaceAll("\\d", "-"));
Pattern p = Pattern.compile("[a-z]{3}");
Matcher m = p.matcher("fgh");
p(m.matches());
p("fgha".matches("[a-z]{3}"));
*/
//初步认识. * + ?
/*
p("a".matches("."));
p("aa".matches("aa"));
p("aaaa".matches("a*"));
p("aaaa".matches("a+"));
p("".matches("a*"));
p("aaaa".matches("a?"));
p("".matches("a?"));
p("a".matches("a?"));
p("214523145234532".matches("\\d{3,100}"));
p("192.168.0.aaa".matches("\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}"));
p("192".matches("[0-2][0-9][0-9]"));
*/
//范围
/*
p("a".matches("[abc]"));
p("a".matches("[^abc]"));
p("A".matches("[a-zA-Z]"));
p("A".matches("[a-z]|[A-Z]"));
p("A".matches("[a-z[A-Z]]"));
p("R".matches("[A-Z&&[RFG]]"));
*/
//认识\s \w \d \
/*
p(" \n\r\t".matches("\\s{4}"));
p(" ".matches("\\S"));
p("a_8".matches("\\w{3}"));
p("abc888&^%".matches("[a-z]{1,3}\\d+[&^#%]+"));
p("\\".matches("\\\\"));
*/
//POSIX Style
//p("a".matches("\\p{Lower}"));
//boundary
//^在【】中表示非的意思，在外面表示开头的意思
/*
p("hello sir".matches("^h.*"));
p("hello sir".matches(".*ir$"));
p("hello sir".matches("^h[a-z]{1,3}o\\b.*"));
p("hellosir".matches("^h[a-z]{1,3}o\\b.*"));
//whilte lines
p(" \n".matches("^[\\s&&[^\\n]]*\\n$"));
p("aaa 8888c".matches(".*\\d{4}."));
p("aaa 8888c".matches(".*\\b\\d{4}."));
p("aaa8888c".matches(".*\\d{4}."));
p("aaa8888c".matches(".*\\b\\d{4}."));
*/
//p("[email protected]".matches("[\\w[.-]]+@[\\w[.-]]+\\.[\\w]+"));
//matches find lookingAt
//matches是找整个字符串，find是找字串，lookingAt每次从头开始找
//matches和find一起用可能会产生冲突，matches之后find接着从matches不匹配//的位置开始找，因此要用reset一下
/*
Pattern p = Pattern.compile("\\d{3,5}");
String s = "123-34345-234-00";
Matcher m = p.matcher(s);
p(m.matches());
m.reset();
p(m.find());
p(m.start() + "-" + m.end());
p(m.find());
p(m.start() + "-" + m.end());
p(m.find());
p(m.start() + "-" + m.end());//用的时候确保能够找的出来，不然用这个方法会报错
p(m.find());
//p(m.start() + "-" + m.end());
p(m.lookingAt());
p(m.lookingAt());
p(m.lookingAt());
*/
//replacement
/*
Pattern p = Pattern.compile("java", Pattern.CASE_INSENSITIVE);
Matcher m = p.matcher("java Java JAVa JaVa IloveJAVA you hateJava afasdfasdf");
StringBuffer buf = new StringBuffer();
int i=0;
while(m.find()) {
i++;
if(i%2 == 0) {
m.appendReplacement(buf, "java");
} else {
m.appendReplacement(buf, "JAVA");
}
}
m.appendTail(buf);
p(buf);
*/
//group
/*
Pattern p = Pattern.compile("(\\d{3,5})([a-z]{2})");
String s = "123aa-34345bb-234cc-00";
Matcher m = p.matcher(s);
while(m.find()) {
p(m.group());
}
*/
//qulifiers
/*
Pattern p = Pattern.compile(".{3,10}+[0-9]");
String s = "aaaa5bbbb68";
Matcher m = p.matcher(s);
if(m.find())
p(m.start() + "-" + m.end());
else
p("not match!");
*/
//non-capturing groups
/*
Pattern p = Pattern.compile(".{3}(?=a)");
String s = "444a66b";
Matcher m = p.matcher(s);
while(m.find()) {
p(m.group());
}
*/
//back refenrences
/*
Pattern p = Pattern.compile("(\\d(\\d))\\2");
String s = "122";
Matcher m = p.matcher(s);
p(m.matches());
*/
//flags的简写
//Pattern p = Pattern.compile("java", Pattern.CASE_INSENSITIVE);
p("Java".matches("(?i)(java)"));
}
public static void p(Object o) {
System.out.println(o);
}
}