Regular expression summary

Catalog

Regular expressions (regular expression)

1. Extract useful information from a string ：

2. Judge the password input ：

3. Extract Chinese ,int Turn into String, String splicing

4. Find the number of a string in a string （ Four ways ）

5. Enter a string , Count the number of occurrences of each character

 6. Enter two strings to determine whether they are heterogeneous

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Regular expressions (regular expression) It describes one kind string matching The pattern of （pattern）, Can be used to check Check whether a string contains a certain seed string 、 Replace a matched substring or remove a substring from a string that meets a condition, etc .

1. Extract useful information from a string ：

public static void main(String[] args) {
		String url = "http://dyit:8663/pets?username=xjaih458&password=456";
		String[] h = new String[3];
		String[] s = url.split("[?]");
		for (String st : s) {
			System.out.println(st+"\t");
		}
		String[] s1 = s[1].split("[&]");
		h[2] = s1[1].substring(s1[1].indexOf("=")+1);
		h[1] = s1[0].substring(s1[0].indexOf("=")+1);
		
		h[0] = s[0].substring(s[0].indexOf("dyit:")+"dyit:".length(),s[0].indexOf("/pets"));
	
		for (String st : h) {
			System.out.print(st+"\t");
		}
	}

2. Judge the password input ：

public static void main(String[] args) {
		String password = "123546";
		String regex = "[0-9]{6}";// Match the password 
		System.out.println(password.matches(regex));

		// Match cell phone number 
		String num = "17623586478";
		String regex1 = "[1][0-9]{10}";
		System.out.println(num.matches(regex1));
		
		// Match ID number 
		String num1 = "610056888785642682";
		String regex2 = "[1-9][0-9]{16}[0-9X]";
		System.out.println(num1.matches(regex2));
		
		String password1 = "123456zxc789";
		String regex3 = "[0-9a-z]{6,}";
		System.out.println(password1.matches(regex3));
		String regex4 = "[0-9a-z]{6,11}";
		System.out.println(password1.matches(regex4));
		// At least 
		String str = "";
//		String regex5 = "[0-9]+";
		String regex6 = "\\d*";// \w \D
		System.out.println(str.matches(regex6));
		String regex7 = "[0-9]?";//? Express 0 Time or 1 Time 
		System.out.println(str.matches(regex7));
		
		//XY And X|Y Relationship 
		String gender = " A secret ";
		String regex8 = "[ male ]|[ Woman ]|( A secret )";
		System.out.println(gender.matches(regex8));	
	}

summary ：

Order number (.): Matching elimination “\n” Any single character other than .

Numeric character \d： Matches a numeric character . Equivalent to [0-9]. 

Nonnumeric character \D： Matches a non-numeric character . Equivalent to [ˆ0-9].

Word characters \w： Match any word character that includes an underline . Equivalent to “[A-Za-z0-9_]”

Nonword character \W ： Match any non word character . Equivalent to “[ˆA-Za-z0-9_]”.

* Number ： Match the previous subexpression Zero or more times .

+ Number ： Match the previous subexpression Once or more .

? Number ： Match the previous subexpression Zero or one .

{n}：n Is a non negative integer . Matched definite Just right n Time .

{n,}：n Is a non negative integer . matching At least n Time .

{m,n} ：m,n Is a nonnegative integer . matching At least m Time , at most n Time .

XY matching ： First match X Match again Y

X|Y matching ： matching X Or match Y,(group) Brackets denote a set of

3. Extract Chinese ,int Turn into String, String splicing

String str = "8w5wf4f7wfe1 stay aaj Go to s56a4 Card hobby 5s";
		String regex = "[^\u4e00-\u9fa5]";// Extract Chinese 
		
		String s = str.replaceAll(regex, "");
		System.out.println(s);
		
		int a = 5;//int Convert to String
		String s1 = String.valueOf(a);
		
		String b = "it's my book";
		// Find substrings 
		System.out.println("indexOf=" +b.indexOf("book"));
		System.out.println("endsWith=" +b.endsWith("book"));
		System.out.println("concat=" +b.contains("book"));
		
		// String splicing 
		String k = "tom";
		String l = "good";
		
		String j = k+l;
		System.out.println("+--->"+j);
		System.out.println("concat--->"+ k.concat(l));
		System.out.println("join--->"+ String.join("?", k,l));

4. Find the number of a string in a string （ Four ways ）

// The first set of methods 
		String h = str1.replaceAll("apple", "#");
		System.out.println(h.replaceAll("[^#]", "").length());
		
		
		// The second method 
		int index = 0;
		int count = 0;
		while(true){
			index = str1.indexOf("apple",index);
			if(index == -1) {
				break;
			}else {
				count++;
				index+="apple".length();
			}
		}
		System.out.println("apple="+ count);
		
		// The third method 
		int o = 0;
		String[] p = str1.split("[ ,]");
		for (String st : p) {
			System.out.print(st);
			if(st.contains("apple")) {
				o++;
			}
		}
		System.out.println("\napple："+ o);
		
		
		d(str1);
		System.out.println(u);
	}

	// Recursive method 
	static int u = 0;
	public static void d(String str) {
		int index1 = str.indexOf("apple");
		if(index1 == -1) {
			return ;
		}
		u++;
		d(str.substring(index1+"apple".length()));
	}

5. Enter a string , Count the number of occurrences of each character

int[] arr = new int[127];
		String str="fhjghftgvgghgvgvfgj$^&#@()*!as12";
		
		for(int i = 0;i<str.length();i++) {
			char ch = str.charAt(i);
			arr[ch] +=1;		
			}
		System.out.println(Arrays.toString(arr));
		
		int pos = 0;
		for(int i = 0;i<arr.length;i++) {
			if(arr[pos]<arr[i]) {
				pos=i;
			}
			System.out.println((char)(i)+" appear ："+arr[i]+" Time ");
			
		}
		System.out.println(" What appears most is ："+(char)pos);
		

 6. Enter two strings to determine whether they are heterogeneous

String a = "hello";
		String b = "hoell";
        int[] chs1= new int[26];
		int[] chs2= new int[26];
		for(int i = 0;i<a.length();i++) {
			char ch1 = a.charAt(i);
			chs1[ch1-'a']+=1;
			char ch2 = b.charAt(i);
			chs2[ch2-'a']+=1;
		}
		System.out.println(Arrays.toString(chs1));
		System.out.println(Arrays.toString(chs2));
		System.out.println(Arrays.equals(chs1, chs2));
		
		
		// Sorting method 
		char[] chs3 = a.toCharArray();
		char[] chs4 = b.toCharArray();
		Arrays.sort(chs3);// Sort 
		System.out.println(Arrays.toString(chs3));
		Arrays.sort(chs4);
		System.out.println(Arrays.toString(chs4));