If you need to represent a set of strings according to specific rules, use regular expressions. Regular expressions can use strings to describe rules and be used to match strings
Java provides the standard library java.util.regex , which can easily use regular expressions.
If the regular expression has special characters, it needs to be escaped with \, which will be mentioned later.
number
Match numbers
Use \d to match one digit. The writing method is \\d ,
String regex1 = "\\d\\d\\d";
System.out.println("110".matches(regex1)); // true
System.out.println("119".matches(regex1)); // true
System.out.println("120".matches(regex1)); // true
System.out.println("1200".matches(regex1)); // false
System.out.println("12F".matches(regex1)); // false
Whether it is an 11-digit number, a common scenario is to determine the mobile phone number.
String regex2 = "\\d{11}";
System.out.println("12345678900".matches(regex2));// true
System.out.println("123456789001".matches(regex2));// false
System.out.println("1234567890a".matches(regex2));// false
System.out.println("A2345678900".matches(regex2));// false
Match non-digits
Use \D to match a non-digit, the writing method is \\D,
String regexD = "\\D\\D";
System.out.println("66".matches(regexD));// false
System.out.println("1*".matches(regexD));// false
System.out.println("1@".matches(regexD));// false
System.out.println("1#".matches(regexD));// false
System.out.println("$$".matches(regexD));// true
Match numbers 0-9
Use [0-9] to match one digit,
String regexd09 = "[0-9][0-9]";
System.out.println("11".matches(regexd09));// true
System.out.println("110".matches(regexd09));// false
System.out.println("1A".matches(regexd09));// false
System.out.println("AA".matches(regexd09));// false
Extension, use [5-8] to match numbers 5-8,
String regexd58 = "[5-8][5-8]";
System.out.println("55".matches(regexd58));// true
System.out.println("88".matches(regexd58));// true
System.out.println("66".matches(regexd58));// true
System.out.println("59".matches(regexd58));// false
System.out.println("48".matches(regexd58));// false