Tag Archives: java

Setting up SonarQube for Android Gradle project to improve code quality

I’m working on a new Android project which I inherited. Well, I forked it because I didn’t feel welcomed to contribute to the project and I see a lot of places where improvements are needed.

First, I need to improve the codebase. Previous developers didn’t care about any Java coding guidelines from Oracle, Google, CERT or even Android. Some of the problems I have to solve now are:

  • inconsistent style
  • catch (Exception e){}
  • catch(Throwable e){}
  • ArrayList<Object> list = new ArrayList<String>()
  • complex methods – if {switch {for {if {else {}}}}
  • new Thread().start()

To quickly start clean-up and identify those problems, different static code analysis tools can be used; one of them is SonarQube.

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[Java] – Regular expression to match IPv4 address

I saw such question on SO. There was no solution with RegEx so… I was bored I think.

public static boolean isValid(String ip) {
    boolean isvalid;
    isvalid = ip.matches(
            "(([0-9]|[0-9]{0,2}|1[0-9]*{0,2}|2[0-5][0-5]|0{0,3}).){3}" +
    return isvalid;

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[Java] regular expression to match emails and domains works with gTLD

Recently we got many new top-level domains like .international, .berlin etc, so older regular expressions are no longer valid.
Below you can see a list of valid domains; an address may contain . (dot), – (minus) and .subdomain (domain may contain many sub-domains). A domain must end with a letter, it cannot be . (dot) or a number.

  • site.international
  • site.international.com
  • site.ac.uk
  • site.org
  • site.babia-gora.pl
  • site.pl

Email address may contain a delimiter like – or + and . (dot), it might contain numbers and for sure contain letters. Below is a list of valid email addresses:

  • info9@agilob.net
  • in-fo@site.international
  • in.fo@site.ac.uk
  • in+fo@site.babia-gora.pl
  • 1in-+fo2@site.babia-gora.pl

A regular expression to match gTLD domains can look like this:


and regular expression to match emails in domains above like this:


Code to test those regexpes:

package regexp;
import java.util.ArrayList;
public class RegExpMatcher {
    public static void main(String[] args) {
        ArrayList domains = new ArrayList<>();
        boolean matches;
        System.out.println("Matching domains: ");
        for (int i = 0; i < domains.size(); i++) {
            matches = domains.get(i).matches("^[A-Za-z0-9][A-Za-z0-9.-]*\.*[A-Za-z]$");
            if (matches == true) {
                System.out.println(domains.get(i) + " matches");
            } else {
                System.err.println(domains.get(i) + " doesn't match");
        System.out.println("nnMatching email addresses: ");
        ArrayList emails = new ArrayList&lt;&gt;();
        for (int i = 0; i < emails.size(); i++) {
            matches = emails.get(i).matches("[A-Za-z0-9-+.]*@[A-Za-z0-9][A-Za-z0-9.-]*\.*[A-Za-z]$");
            if (matches == true) {
                System.out.println(emails.get(i) + " matches");
            } else {
                System.err.println(emails.get(i) + " doesn't match");


Matching domains: 
site.international matches
site.international.com matches
site.ac.uk matches
site.org matches
site.babia-gora.pl matches
site.pl matches

Matching email addresses: 
info9@agilob.net matches
in-fo@site.international matches
in.fo@site.ac.uk matches
in+fo@site.babia-gora.pl matches
1in-+fo2@site.babia-gora.pl matches

Solution to SQLException: No suitable driver found for jdbc:mysql

Just a quick fix.

Instead of:

Connection con = null;
String url = "jdbc:mysql://localhost:3306/mysql";
String user = "user";
String password = "password";
con = DriverManager.getConnection(url, user, password);

You should have:

Connection con = null;
String url = "jdbc:mysql://localhost:3306/mysql";
String user = "user";
String password = "password";
try {
} catch (Exception ex) {
con = DriverManager.getConnection(url, user, password);

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AberPizza in Java

AberPizza – simple cash register for small pizzerias. Application made as a first year, second semester assignment.

Application has a built-in database of products and prices, can add those product to an order, give discount in GBP or in percentage of the whole order.

Bills are stored in XML files and can be loaded into the application to print receipt.

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