Top Java Tutorial

Java program to detect a cycle in a singly LinkedList

In this article, we will learn how to detect a cycle or loop in a Linkedlist. We will be using Floyd’s cycle finding algorithm also know an the “tortoise and the hare algorithm”   Floyd’s Tortoise and Hare algorithm Floyd’s cycle-finding algorithm is a pointer algorithm that uses two pointers, which move through the sequence at different speeds. If the two pointers refer to the same node at some…

How to get current date time (today’s date) in Java

In this article, we will discuss how to get current date and time using the legacy Date and Calendar apis alongwith the Java 8 LocalDate, LocalTime, LocalDateTime and ZonedDateTime apis. Current date using java.util.Date instance Date d1 = new Date(); System.out.println(d1); // Tue Mar 06 22:50:37 EST 2018 If you are looking to format the current date in a specific format, use the…

Spring Boot – CRUD operations using JPA

In this article, we will use the JPA (Java Persistence API) with Spring Boot for insert, update, delete and read operations. We are using in-memory H2 database, but the same can be changed for any other relational database.   Project Structure We can use Spring Tool Suite(STS) to create a Spring starter project and choose the h2 and jpa dependencies. We can also use Spring Initializr for the same…

Java program to remove duplicate characters from a String

In this article, we will discuss how to remove duplicate characters from a String. Here is the expected output for some given inputs : Input : topjavatutorial Output : topjavuril Input : hello Output : helo The below program that loops through each character of the String checking if it has already been encountered and ignoring it if the condition is true. package com.topjavatutorial; public…

Java program to find Longest Common Subsequence

Longest Common Subsequence Problem This problem looks to find the longest common subsequence between two strings. This is not same as finding longest common substring between two strings. While substrings occupy consecutive positions, subsequences can be in random order and need not take consecutive positions.   Recursive solution for Longest Common Subsequence package com.topjavatutorial; public…

10+ Java Letter / Character Pattern Programs

In Java, we can use for loop, while loop or do-while loops to print different number, alphabet or star patterns programs. Here are some examples for character or letter pattern programs. For other patterns, please refer the links at the end of the post. Character Pattern Program 1: A BC DEF GHIJ KLMNO class CharPattern1 { public static void main(String[] args) { char ch = 'A'; for (int i = 1; i…

In this article, we try to address a frequently encountered error with regular expression in java : PatternSyntaxException: Unclosed character class The following example demonstrates this : import java.util.regex.Matcher; import java.util.regex.Pattern; public class Hello { public static void main(String[] args) { String regex = "[a-zA-Z\\]*$"; String value = "hello"; boolean match =…

Spring Boot Microservice – How to fix “BindException: Address already in use: bind” error

If you are getting the following error while starting your spring-boot application, this means the 8080 port is being used by another application. You can stop the other application, or follow the approach mentioned below. java.net.BindException: Address already in use: bind at sun.nio.ch.Net.bind0(Native Method) at sun.nio.ch.Net.bind(Net.java:433) at sun.nio.ch.Net.bind(Net.java:425) at…

Android Studio – Gradle project refresh/sync failed : connection timed out

This article tries to address following issues while starting Android Studio Gradle sync failed: Connection timed out   Gradle project refresh failed : connection timed out If you are getting this error while starting Android studio, it will be mostly because its not able to connect to Internet. Check if you are able to connect to internet from Android Studio. For this, go to File -> Settings…

Spring Boot : Adding basic security to microservices

In this article, we will add basic authentication to a previous Spring application we created in this post : Spring Boot Hello World Adding maven dependency Add the following dependency to the pom.xml : org.springframework.boot spring-boot-starter-security This will add the following jars to the maven : spring-security-config-X.X.X.RELEASE.jar spring-security-core-X.X.X.RELEASE.jar…

How to integrate Swagger 2 with Spring Boot

In this article, we will see how to integrate Swagger 2 with Spring Boot to generate a simple api documentation. What is Swagger ? Swagger is set of open source tools that helps with creating documentation for your REST services. Lets start with creating a Spring Tool Web application. You can refer the following article for the same. Spring Boot Hello World Web Application   Adding Swagger 2…

How to fix “Source folder is not a Java project” error in eclipse

If you are creating a maven web project in eclipse and get a “Source folder is not a Java project” error, here is how to fix that : To fix this, right click on your project and select Properties -> Project Facet Click on “convert to faceted form” Select “Java” and click on “Apply and Close” and you should see the java source folder package structure in the project.  

How to configure proxy in Eclipse

If you are behind a proxy and want Eclipse to connect to internet for some plugins like STS(Spring Tool Suite), follow the following steps : In Eclipse menu bar, go to Window -> Preference. Select General -> Network Preferences. Switch the provider to “manual” and update the HTTP and HTTPS entries for the proxy host and port. Provide user id & pwd if you need to authenticate to use the proxy. You…

Handlebars.js – How to escape or display special html characters

Handlebars by default escapes special characters. So, if you trying to print special characters like ™ or ® etc, they will be escaped and the corresponding html codes will be printed. For example , Handlebars js Output : Note that, the above example doesnot print the ™ symbol. Rather, it prints the html characters as is. However, if you don’t want Handlebars to escape a value, use the…

Handlebars.js – Partials

Handlebars allows code reuse using Partials. A Partial is a common template that can be included in another template. To create and register a partial, the method Handlebars.registerPartial() can be used as show below : Handlebars.registerPartial("messagePartial","Employee : {{name}}, Age : {{age}}" ); The first parameter to registerPartial() is the name of the partial template and second…

Handlebars.js – Unless helper

The unless helper in handlebars works as “if not”. So, the block under the unless helper will be rendered if the expression passed is false. For example, the following code will display the block of text “No name element present” only if name is not available in the context. {{#unless name}} No name element present {{/unless}} Here is the complete example : Handlebars js In the above data passed,…

Handlebars.js – Creating Custom Helpers

Handlebars Helpers Helpers in Handlebars.js are reusable functions that can be added to data to change its behavior in some way. Handlebars provides several built-in helpers such as if, each, unless etc. (For built-in helper, refer http://handlebarsjs.com/builtin_helpers.html)   Creating custom Handlebars Helpers We can create our own helper functions in Handlebars using the registerHelper()…