正则表达式
申明：正则表达式可以大大的简化代码，不过对于看不懂的人来说，那也只能骂娘。切身体会，所以感觉有必要撸下来正则表达式！（后期会不断添加各种正则判断）
基本概念不多说我，直接上例子，通过例子说明吧。
一、正则基础
Demo1:
在java中对反斜线\的处理与其它语言不同，在其它语言中,\\表示“我想要在正则表达式中插入一个普通的（字面上的）反斜线”，请不要给它任何特殊的意义。而在java中，\\的意思是“我要插入一个正则表达式的反斜线，所以其后的写符具有特殊的意义。"例如，如果我想要表示一位数字，那么正则表达式应该是\\d。如果你想插入一个普通的反斜线，则应该这样\\\\，不过换行和制表之类的东西只需要使用单反斜线：\n\t
package com.rah; /*** * * @author team * */ public class Demo1 { public static void main(String[] args) { /*** * 反斜线\在程序中必须以\\表示如下： */ System.out.println("\\".matches("\\\\")); /*** * ("-?\\d+")匹配：可能有一个负号，或者后面跟着一位或多位数字 */ System.out.println("-1234".matches("-?\\d+")); System.out.println("5678".matches("-?\\d+")); System.out.println("+911".matches("-?\\d+")); /*** * ("(-|\\+)?\\d+")匹配:表示字符串的起始字符可能是一个-或者+（+有特殊意义，需要用\\转义）,后面跟着一位或多位数字 */ System.out.println("+911".matches("(-|\\+)?\\d+")); } }
运行结果：
true true true false true
Demo2
String.spilt是一个非常有用的正则表达式工具，其功能是”将字符串从正则表达式匹配的地方切开“。
package com.rah; import java.util.Arrays; /*** * * @author team * */ public class Demo2 { public static String knights = "Then, when you have found the shrubbery, you must " + "cut down the mightiest tree in the forest..." + "with... a herring!"; public static void split(String regex) { System.out.println(Arrays.toString(knights.split(regex))); } public static void main(String[] args) { /*** * 按空格划分字符串 */ split(" "); /*** * \W(\\W转义)意思是非单词字符如果是小写W，\w则表示一个单词字符 * 该正则可以标点字符给删了 */ split("\\W+"); /*** * 字母n后面跟着一个单词字符 */ split("n\\W+"); } }
运行结果：
[Then,, when, you, have, found, the, shrubbery,, you, must, cut, down, the, mightiest, tree, in, the, forest...with..., a, herring!]
[Then, when, you, have, found, the, shrubbery, you, must, cut, down, the, mightiest, tree, in, the, forest, with, a, herring]
[The, whe, you have found the shrubbery, you must cut dow, the mightiest tree i, the forest...with... a herring!]
Demo3
String.replaceFirst()/replaceAll(),也是可以匹配正则的
package com.rah; /*** * * @author team * */ public class Demo3 { public static String sqlOne = "select * from students"; public static String sqlTwo = "seelct count(*) from students"; public static void main(String[] args) { /*** * 从前四个输出可以看出[]里面是只匹配他就会在第一时间匹配到就不会往下找，就是因为这个小知识点，在开发中浪费了我好多时间Q_Q */ System.out.println(sqlOne.replaceFirst("s", "count(*)")); System.out.println(sqlOne.replaceFirst("[s]", "count(*)")); /*** * 找到se匹配 */ System.out.println(sqlOne.replaceFirst("se", "count(*)")); /*** * 找到s匹配，就不会往下找 */ System.out.println(sqlOne.replaceFirst("[se]", "count(*)")); System.out.println(sqlOne.replaceFirst("[*]", "count(*)")); System.out.println(sqlTwo.replaceFirst("count\\(\\*\\)", "*")); } }
运行结果：
count(*)elect * from students count(*)elect * from students count(*)lect * from students count(*)elect * from students select count(*) from students seelct * from students
Demo4:
检查句子以大写字母开头、以句号结尾
package com.rah; /*** * * @author team * */ public class Demo4 { public static boolean matches(String text) { /*** * \\p{javaUpperCase} 大写字母，不明白的可以看jdk文档 */ return text.matches("\\p{javaUpperCase}.*\\."); } public static void main(String[] args) { System.out.println(matches("This is correct.")); System.out.println(matches("bad sentence 1.")); System.out.println(matches("Bad sentence 2")); System.out.println(matches("This is also correct...")); } }
运行结果:
true false false true
Demo5:
package com.rah; import java.util.Arrays; /*** * * @author team * */ public class Demo5 { public static String knights = "Then, when you have found the shrubbery, you must " + "cut down the mightiest tree in the forest..." + "with... a herring!"; public static void split(String regex) { System.out.println(Arrays.toString(knights.split(regex))); } public static void main(String[] args) { /*** * 在the和you处分割 */ split("the|you"); } }
运行结果：
[Then, when , have found , shrubbery, , must cut down , mightiest tree in , forest...with... a herring!]
Demo6
package com.rah; /*** * * @author team * */ public class Demo5 { public static String knights = "Then, when you have found the shrubbery, you must " + "cut down the mightiest tree in the forest..." + "with... a herring!"; /* * 对应的内嵌标志表达式是 (?i)，它有四种形式： * 1，(?i) * 2，(?-i) * 3，(?i:X) * 4，(?-i:X) * 不带有 - 的是开标志，带有 - 的是关标志。 */ public static void main(String[] args) { /*** * 对book都忽略大写 */ System.out.println("Book".matches("(?i)Book")); /*** * 对b都忽略大写，ook还是得比较大小写，下面的方法作用一样，写的更简洁 */ System.out.println("Book".matches("(?i)b(?-i)ook")); /*** * 对b都忽略大写，ook还是得比较大小写 */ System.out.println("Book".matches("(?i:b)ook")); /*** * (?-i) 的作用域是前面，如a(?-i) (?-i)的作用域是后面，如(?i)B */ System.out.println("bOOk".matches("b(?-i)(?i)ook")); System.out.println("aBook".matches("a(?-i:B)ook")); /*** * [] 只要匹配到一个再往下匹配，匹配不到了就把当前的替换 * 没有[] 他要满足字符串到匹配到才换 */ System.out.println("ouahoahuah".replaceAll("[ou]", "")); System.out.println("ouahoahuah".replaceAll("ou", "")); /*** * 忽略大小写匹配aeiou */ System.out.println(knights.replaceAll("(?i)[aeiou]", "")); } }
运行结果：
true true true true true ahahah ahoahuah Thn, whn y hv fnd th shrbbry, y mst ct dwn th mghtst tr n th frst...wth... hrrng!
二、创建正则表达式
写法参考java.util.regex包下的Pattern类
Demo7:
package com.rah; import java.util.regex.Matcher; import java.util.regex.Pattern; public class Demo7 { public static void main(String[] args) { if(args.length<2){ System.out.println("Usage:\njava TestRegularExpression " + "characterSequence regularExpression"); System.exit(0); } System.out.println("Input: \"" + args[0] + "\""); for(String arg : args){ System.out.println("Regulqr expression: \"" +arg +"\""); Pattern p = Pattern.compile(arg); Matcher m = p.matcher(args[0]); while(m.find()){ System.out.println("Match \"" + m.group() + "\" at position " + m.start() + "-" + (m.end()-1)); } } } }
传入的参数：
abcabcabcdefabc abc+ (abc)+ (abc){2,}
运行结果：
Input: "abcabcabcdefabc" Regulqr expression: "abcabcabcdefabc" Match "abcabcabcdefabc" at position 0-14 Regulqr expression: "abc+" Match "abc" at position 0-2 Match "abc" at position 3-5 Match "abc" at position 6-8 Match "abc" at position 12-14 Regulqr expression: "(abc)+" Match "abcabcabc" at position 0-8 Match "abc" at position 12-14 Regulqr expression: "(abc){2,}" Match "abcabcabc" at position 0-8
Demo8:
package com.rah; import java.util.regex.Matcher; import java.util.regex.Pattern; /*** * * @author team * */ public class Demo8 { public static void main(String[] args) { Matcher m = Pattern.compile("\\w+").matcher("Evening is full of the linnet's wings"); while(m.find()) System.out.print(m.group() + " "); System.out.println(); int i = 0; /*** * find(args) 是字符的起始位置，注意输出结果 */ while(m.find(i)) { System.out.print(m.group() + " "); i++; } } }
运行结果：
Evening is full of the linnet s wings
Evening vening ening ning ing ng g is is s full full ull ll l of of f the the he e linnet linnet innet nnet net et t s s wings wings ings ngs gs s
Demo9 （Group组）
组是用括号提供划分的正则表达式，可以根据组的编号来引用某个组。组号为0表示整个表达式组号为1表示被第一对括号括起来的组。
a(b(c))d abcd是组0 bc是组1 c是组2
package com.rah; import java.util.regex.Matcher; import java.util.regex.Pattern; /*** * * @author team * */ public class Demo9 { static public final String POEM = "Twas brillig, and the slithy toves\n" + "Did gyre and gimble in the wabe.\n" + "All mimsy were raths outgrabe.\n" + "And the mome raths outgrabe.\n\n" + "Beware the Jabberwock, my son,\n" + "The jaws that bite, the claws that catch.\n" + "Beware the Jubjub bird, and shun\n" + "The frumious Bandersnatch."; public static void main(String[] args) { /*** * 检索每行的3个单词，每行最后以$结尾。通常$是与整个输入序列的末端进行匹配的，为了达到每行最后以$结尾，我们需要显示的通知正则表达式注意输入 * 序列中的换行符，这个工作就由模式标记(?m)来完成。 */ Matcher m = Pattern.compile("(?m)(\\S+)\\s+((\\S+)\\s+(\\S+))$").matcher(POEM); while(m.find()) { for (int i = 0; i <= m.groupCount(); i++) { System.out.print("[" + m.group(i) + "]" + " "); } System.out.println(); } } }
运行结果：
[the slithy toves] [the] [slithy toves] [slithy] [toves] [in the wabe.] [in] [the wabe.] [the] [wabe.] [were raths outgrabe.] [were] [raths outgrabe.] [raths] [outgrabe.] [mome raths outgrabe.] [mome] [raths outgrabe.] [raths] [outgrabe.] [Jabberwock, my son,] [Jabberwock,] [my son,] [my] [son,] [claws that catch.] [claws] [that catch.] [that] [catch.] [bird, and shun] [bird,] [and shun] [and] [shun] [The frumious Bandersnatch.] [The] [frumious Bandersnatch.] [frumious] [Bandersnatch.]
Demo10
?:、?!、?s、?i、?x、?m、?u、?d等的使用
未完待续。。。