Чашечка Java

How to Fix java.lang.NoClassDefFoundError: org/dom4j/DocumentException [Solution] Exception in thread "main" java.lang.NoClassDefFoundError: org/dom4j/DocumentException comes when your program is using the DOM4j library but necessary JAR is not present. This error can also come when you are indirectly using the DOM4j library like  when you use the Apache POI library to read the XLSX file in Java,  this library needs dom4j.jar in your classpath. Not just this one but there are several other libraries that use this JAR internally, if you are using any of them but don't have this JAR then your program will compile fine but fail at runtime because JVM will try to load this class but will not be able to find it on the classpath. Java Interview questions and tutorials Read: http://www.java67.com/2015/06/org.dom4j.DocumentException-javalangnoclassdeffounderror.html

java.lang.NoClassDefFoundError: org/apache/xmlbeans/XmlObject [Solved] Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/xmlbeans/XmlObject error means that your Java program needed a class called org.apache.xmlbeans.XmlObject but JVM is not able to find that in your application's CLASSPATH. You can see the actual cause of this error is "java.lang.ClassNotFoundException: org.apache.xmlbeans.XmlObject". The most probable reason for this error could be a missing JAR file. In order to solve this error, you need to first find out which JAR file this class belongs. If you look at the error message it's clearly saying that it's from xmlbeans package, it means this class belongs to XMLBeans library. Java Interview questions and tutorials Read: http://www.java67.com/2015/06/OrgApachexmlbeansXmlObjectNoClassDefFoundErrorClassNotFoundException.html

Быстро сжимаем, быстро пишем и читаем! На Java В ходе разработки IDE 1С:Enterprise Development Tools у нас возникла необходимость быстро оперировать с довольно большими (несколько гигабайтов) объемами данных. Если не вдаваться в детали: при интерактивной работе пользователя с IDE при переключении с одной ветки репозитория на другую нам нужно сохранить текущее состояние проекта и загрузить состояние проекта из новой ветки. Детали (и объяснение – почему счет идет на гигабайты) — в конце статьи, непосредственно к Java это отношения не имеет, кому интересно – прочтет. Ну а что касается Java, то задача выглядит так: быстро сохранить несколько гигабайт информации на диск и быстро считать несколько гигабайт информации с диска. Как мы решали эту задачу, с какими трудностями столкнулись и как их преодолели – под хабракатом. Читать: https://habr.com/ru/post/680838/?utm_campaign=680838

'javac' is not recognized as an internal or external command [Solution] 'javac' is not recognized as an internal or external command, operable program, or batch fileerror comes when you try to compile a Java source file using the javac command like javac Helloworld.java but your PATH is not set properly. It means that the javac.exe executable file, which exists in the bin directory of the JDK installation folder is not added to the PATH environment variable. You need to add the JAVA_HOME/binfolder in your machine's PATH to solve this error. You cannot compile and run a Java program until your add Java into your system's PATH variable. Java Interview questions and tutorials Read: http://www.java67.com/2015/07/javac-is-not-recognized-as-internal-or-external-command-program-batch-file.html

How to Fix java.lang.OufOfMemoryError: Direct Buffer Memory Java allows an application to access non-heap memory by using a direct byte buffer. Many high-performance applications use a direct byte buffer, along with a memory-mapped file for high-speed IO. And, while the ByteBuffer object is small itself, it can hold a large chunk of non-heap memory, which is outside of the Garbage collection scope.  This means the garbage collectors can not reclaim this memory. It is often used to store large data like order or static data cache. Since generally, your program allocates the large buffer e.g. size of 1GB or 2GB, you get "Exception in thread "main" java.lang.OutOfMemoryError: Direct buffer memory" error, when you try to allocate memory by running the following code Java Interview questions and tutorials Read: http://www.java67.com/2014/01/how-to-fix-javalangoufofmemoryerror-direct-byte-buffer-java.html

java.lang.OutOfMemoryError: Java heap space : Cause and Solution So you are getting java.lang.OutOfMemoryError: Java heap space and run out of ideas on what to do, especially if you are a user of any Java application and not the programmer or developer, this could be a tricky situation to be in. I receive lots of emails from Minecraft user ( a popular Java game), along with junior developers who are using Tomcat, Jetty, Untow, JBoss, WebSphere, Android user, who uses Android apps and several other Swing-based Java desktop application user complaining about java.lang.OutOfMemoryError: Java heap space in their Mobile or Laptop. Java Interview questions and tutorials Read: http://www.java67.com/2013/08/guide-of-javalangoutofmemoryerror-java-heap-space-tomcat-eclipse-minecraft-jboss.html

Исследуем граф «мир тесен» при помощи Neo4j Когда моя сестра переехала в другой город и познакомилась с соседями, оказалось, что дедушка и бабушка ее соседа и наши бабушка с дедушкой были хорошими друзьями и общались, живя рядом в другом городе – два поколения назад. Интересно, когда обнаруживаются такие неожиданные связи. Согласно теории сетей, пути, соединяющие узлы сети, зачастую короче, чем могло бы показаться. Если каждый в сети знает k других людей, то можно упрощенно предположить, что, начав от этого человека и совершив n переходов от узла к узлу, мы найдем kⁿ человек. Учитывая экспоненциальный рост, потребуется совсем немного времени, чтобы построить путь от любого конкретного человека до любого другого в графе. Но в реальных социальных сетях многие люди, знакомые конкретному человеку, также знают друг друга. Такое пересечение между друзьями друзей снижает количество новых людей, к которым я могу обратиться после каждого перехода на пути от стартового узла.  Может быть непросто найти такие пути, которые начинаются в сплоченном сообществе, а далее разветвляются до самых отдаленных уголков сети. В главе 20 книги Networks Crowds and Markets ее авторы Дэвид Изли и Джон Клейнберг дают теоретический аппарат, описывающий, как в реальном мире могут возникать феномены, укладывающиеся в граф «мир тесен». В этой теории сочетается идея гомофилии, согласно которой схожие люди кучкуются вместе, и идея слабых связей, где отношения ветвятся в масштабах всей сети. Объяснение основано на работе Дункана Уоттса и Стива Строгаца. Давайте проследим эти примеры при помощи кода, написанного при помощи Neo4j. Читать: https://habr.com/ru/post/680576/?utm_campaign=680576

Top 30 Gradle Interview Questions with Answers for beginners and experienced Hello guys, if you are preparing for Java or Kotlin developer interview where Gradle skills are needed then you should prepare for Gradle related questions. I have seen many interviewer asking Maven and Gradle related questions during interviews and many Java developer don't prepare them. But, considering you are looking for Gradle questions I think you are one step ahead of them and If you are looking for Gradle interview questions then you have come to the right place. Earlier, I have shared Maven Interview Questions and in this article, I am going to share Gradle interview questions for Java and Kotlin developers. Java Interview questions and tutorials Read: http://www.java67.com/2022/08/gradle-interview-questions-with-answers.html

[Solved] How to Fix StringIndexOutOfBoundsException 1 and ArrayIndexOutOfBoundsException in Java? Though both StringIndexOutOfBoundsException and ArrayIndexOutOfBoundsException are children of IndexOfBoundsExceptionclass, the former is thrown by methods of String and related class like StringBuffer and StringBuilder to indicate that an index is either negative or greater than the size of the String, or more generally not valid. For example, charAt() method throws StringIndexOutOfBoundsException when an index is equal to the length of String? why? because String is backed by character array where index starts at 0and ends at length -1. Java Interview questions and tutorials Read: http://www.java67.com/2016/04/difference-between-stringindexoutofboundsException-vs-ArrayIndexOutOfBoundsException-Java.html

How to fix "class, interface, or enum expected" error in Java? Example If you have ever written Java programs using Notepad or inside DOS editor, then you know that how a single missing curly bracecan blow your program and throw 100s of "illegal start of expression" errors during compilation of Java Programmer. I was one of those lucky people who started their programming on DOS editor, the blue window editor which allows you to write Java programs. I didn't know about PATH, CLASSPATH, JDK, JVM, or JRE at that point. It's our lab computer where everything is supposed to work as much as our instructor wants. Java Interview questions and tutorials Read: http://www.java67.com/2016/08/how-to-fix-class-interface-or-enum-expected-error-java.html

How to fix "illegal start of expression" error in Java? Example The "illegal start of expression"error is a compile-time error when the compiler finds an inappropriate statement in the code. The java compiler, javac, compile your source code from top to bottom, left to right and when it sees something inappropriate at the start of an expression, it throws an "illegal start of expression"error. The most common reason for this is a missing semi-colon. You might know that every statement in Java ends with a semicolon, but if you forget one, you won't get an error that there is a missing semi-colon at the end of the statement because the compiler doesn't know the end. Java Interview questions and tutorials Read: http://www.java67.com/2016/08/how-to-fix-illegal-start-of-expression-error-in-java.html

How to deal with Unsupported major.minor version 55.0, 57,0, 60.0, 61.0 in Java + Eclipse + Linux [Solution] The "unsupported major.minor version 55.0"error started to come after Java SE 11 release and the root cause of this error is trying to run a Java application compiled with JDK 11 into a JRE lower than Java SE 11 like JRE 9 or JRE 8. This is very common because a developer has updated their compiler or IDE to Java SE 11 but many times their runtime is not upgraded to Java 11. If you remember, in Java you can run a class file compiled with a lower version say Java 8 to a higher version say JRE 11 because Java is backward compatible but vice-versa is not allowed. I mean, you cannot run a JAR file or class file created by Java 11 version into  Java 8 or Java 9 version. Similarly, you cannot run a Java SE 17 compiled class file in Java SE 11 or Java SE 13 runtime environment. Java Interview questions and tutorials Read: http://www.java67.com/2016/06/unsupported-majorminor-version-520-in-java-eclipse-linux.html

[Solved] java.lang.unsupportedclassversionerror Unsupported major.minor version 55.0, 57.0, 60.0, 61.0 Error in Java? Examples The java.lang.unsupportedclassversionerror unsupported major.minor version 60.0 error comes in Java environment when you compile your Java file in a higher Java version like Java 16 and then trying to run the same Java program in lower Java version like Java 11. Java is backward compatible, I mean you can run your Java 15 binary or JAR into Java or JRE 16 but vice-versa is not true. You can not run a Java program that is compiled in a higher Java version into lower JRE. class file version changes between every Java version and class file generated by the javac command of Java 16 installation is not appropriate for JRE of Java 15 Installation. Java Interview questions and tutorials Read: http://www.java67.com/2012/10/how-to-fix-javalangunsupportedclassversionerror-major-minor-version-49-50-51.html

How to deal with java.net.SocketException: Broken pipe, Connection reset, and Too many open files in Java? [Solution] In this blog, I plan to talk about some common exceptions and errors that arise while using sockets. Quite often, these socket issues arise out of application bugs, system settings, or system load. It might be an unnecessary delay to go to product teams, only to discover that the issue can be resolved by tuning/configuring your local settings. Understanding these messages will not only help resolve the issues but also make a conscious effort in avoiding these scenarios while developing applications. Java Interview questions and tutorials Read: http://www.java67.com/2019/02/7-common-socket-errors-and-exception-in-java.html

How to solve java.sql.BatchUpdateException: String or binary data would be truncated in Java JDBC? [Solution] Recently I was working in a Java application that uses Microsoft SQL Server at its backend. The architecture of the Java application was old i.e. even though there was heavy database communication back and forth there was no ORM used like no Hibernate, JPA, or Apache iBatis. The Java application was using an old DAO design pattern, where the DB related classes which are responsible for loading and storing data from the database was calling the stored procedure to do their job. These stored procedures take data from Java applications and insert it into SQL Server tables. Java Interview questions and tutorials Read: http://www.java67.com/2016/10/how-to-solve-javasqlbatchupdateexception-string-or-binary-data-would-be-truncated.html

How to Fix Reference Error: $ is not defined in jQuery and JavaScript [Solved] Hello JavaScript developer, if you are wondering how to fix the Reference Error $ is not defined while using jQuery then you have come to the right place. "Reference Error: $ is not defined" is one of the common JavaScript errors which come when you try to use $, which is a shortcut of jQuery() function before you load the jQuery library like calling $(document).ready() function. "ReferenceError: XXX is not defined"is a standard JavaScript error, which comes when you try to access a variable or function before declaring it. Since jQuery is also a JavaScript library, you must first include the declaration of the jQuery function or $() before you use it. Java Interview questions and tutorials Read: http://www.java67.com/2020/07/fixing-referenceerror-is-not-defined-in.html

How to Fix SQLServerException: The index is out of range? JDBC Example I was executing a stored procedure against SQL SERVER 2008 database from Java program using CallableStatement, but unfortunately, I was getting the following error "SQLServerException: The index 58 is out of range". Since I am passing a lot of parameters I thought that something is wrong with a number of parameters I was passing to the stored proc. My stored procedure had 58 INPUT parameters, as soon as I removed the 58th INPUT parameter the error goes away, which confirmed my belief that SQL Server supports a maximum of 57 INPUT parameters in stored procedure via JDBC. Java Interview questions and tutorials Read: http://www.java67.com/2015/12/sqlserverexception-index-58-is-out-of-range-SQL-SERVER-stored-proc.html

How to deal with java.lang.NullPointerExceptionin Java? Cause, Solution, and Tips to avoid NPE Hello Java programmers, if you want to learn what is NullPointerExcpeiton in Java and how to deal with NullPointerException or NPE then you have come to the right place. NullPointerException in Java is an unchecked Exception defined in java.lang package and comes when a member of an object either field or method is called on an object which is null. null is a keyword in Java that means nothing and the calling method on an object whose value is null will result in NullPointerException. Since the default value of Objectis null, if you call any method or access any field on an Object which is not initialized will throw NullPointerException. Java Interview questions and tutorials Read: http://www.java67.com/2021/05/how-to-solve-nullpointerexception-in-java.html

How to fix org.springframework.beans.factory.BeanCreationException: Error creating bean with name X [Java Spring] If you are using the Spring framework in your Java application and getting this error during startup it means Spring is not able to initialize the bean X and add it into its application context, Why? There could be multiple reasons like a typo on the spring bean name. Let's take a closer look at the stack trace to find out the real reason: BeanInstantiationException: Could not instantiate bean class [X]: No default constructor found; nested exception is java.lang.NoSuchMethodException: X.() Here X is the class, which is declared as Spring bean. The error clearly says that the default constructor is not present in class X. Java Interview questions and tutorials Read: http://www.java67.com/2017/07/solving-orgspringframeworkbeansfactoryb-beancreation-exception-java-spring.html