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}."));

              */

             

              //email

              //p("asdfasdfsafsf@dsdfsdf.com".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);

       }

 

}