Java/Regular Expressions/Digit Number

Check if given string is a number (digits only)

public class Main {
  public static boolean isNumber(String string) {
    return string.matches("^\\d+$");
  }
  public static void main(String[] args) {
    System.out.println(isNumber("123"));
  }
}

Check if given string is number with dot separator and two decimals

public class Main {
  public static boolean isNumberWith2Decimals(String string) {
    return string.matches("^\\d+\\.\\d{2}$");
  }
  
  
  public static void main(String[] args) {
  sysout isNumberWith2Decimals("1234.123") 
    
  }
}

Check if given string is numeric (-+0..9(.)0...9)

public class Main {
  public static boolean isNumeric(String string) {
      return string.matches("^[-+]?\\d+(\\.\\d+)?$");
  }
  
  
  public static void main(String[] args) {
sysout isNumeric("123.123")
  }
}

Match a single digit

import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Main {
  public static void main(String args[]) {
    // match a single digit
    Pattern p = Pattern.rupile("\\d");
    Matcher matcher = p.matcher("5");
    boolean isOk = matcher.matches();
    System.out.println("original pattern matches " + isOk);
    // recycle the pattern
    String tmp = p.pattern();
    Pattern p2 = Pattern.rupile(tmp);
    matcher = p.matcher("5");
    isOk = matcher.matches();
    System.out.println("second pattern matches " + isOk);
  }
}

Matcher Pattern number

import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Main {
  public static void main(String args[]) {
    Pattern p = Pattern.rupile("\\d");
    Matcher m1 = p.matcher("55");
    Matcher m2 = p.matcher("fdshfdgdfh");
    System.out.println(m1.pattern() == m2.pattern());
    // return true
  }
}

Match number

import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Main {
  public static void main(String[] argv) throws Exception {
    Pattern number = Pattern.rupile("\\G\\d+\\.?\\d*");
    Matcher mat = number.matcher("this is a test 999");
    System.out.println(mat.find());
  }
}
//false