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
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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+"));
}
}
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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“。
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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+");
}
}
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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
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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\\(\\*\\)", "*"));
}
}
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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
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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..."));
}
}
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运行结果:
true
false
false
true
Demo5:
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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");
}
}
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运行结果：
[Then, when , have found , shrubbery, , must cut down , mightiest tree in , forest...with... a herring!]
Demo6
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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]", ""));
}
}
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运行结果：
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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!
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二、创建正则表达式
写法参考java.util.regex包下的Pattern类
Demo7:
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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));
}
}
}
}
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传入的参数：
abcabcabcdefabc abc+ (abc)+ (abc){2,}
运行结果：
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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
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