If you are using jQuery, Angular JS, or plain old JavaScript and getting "Uncaught ReferenceError: $ is not defined" error which means $ is either a variable or a method that you are trying to use before declaring it using the var keyword. In jQuery, it's a short name of jQuery() function and most commonly used in $(document).ready(function()). If you are doing some jQuery stuff when DOM is loaded and getting this error it means your browser has a problem loading jQuery library either from the internet or local file system. --- Java, Unix, Tibco RV and FIX Protocol Tutorial

Problem: I was trying to run a HelloWorld program using Spring Boot when I got this error: Exception in thread "main" java.lang.IllegalStateException: Could not evaluate condition on org.springframework.boot.autoconfigure.PropertyPlaceholderAutoConfiguration#propertySourcesPlaceholderConfigurer due to internal class not found. This can happen if you are @ComponentScanning a springframework package (e.g. if you put a @ComponentScan in the default package by mistake) at org.springframework.boot.autoconfigure.condition.SpringBootCondition.matches(SpringBootCondition.java:52) at org.springframework.context.annotation.ConditionEvaluator.shouldSkip(ConditionEvaluator.java:92) at org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitionsForBeanMethod(ConfigurationClassBeanDefinitionReader.java:174) at org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitionsForConfigurationClass(ConfigurationClassBeanDefinitionReader.java:136) --- Java Interview questions and tutorials

Hello guys, this is one of the common errors in a client-server application. The big problem in solving this error is not the error but the knowledge of how client-server SSL handshake works. I have blogged about that before and if you have read that you know that in order to connect to any website or server (like LDAP Server) using SSL, you need to have certificates (public keys) to validate the certificates sends by the website you are connecting. If you don't have the root certificate or public key, which is required to validate the certificate presented by the server in your JRE truststore then Java will throw this error. --- Java Interview questions and tutorials

java.io.NotSerializableException: org.apache.log4j.Logger error says that an instance of org.apache.lo4j.Logger is not Serializable. This error comes when we use log4j for logging in Java and create Logger in a Serializable class e.g. any domain class or POJO which we want to store in HttpSession or want to serialize it. As we know from 10 Java Serialization interview question that, if you have a non serializable class as member in a Serializable class, it will throw java.io.NotSerializableException Exception. --- Java, Unix, Tibco RV and FIX Protocol Tutorial

The "Exception in thread "main" java.lang.NoClassDefFoundError: helloworldapp/HelloWorldApp" error comes when you are trying to run the HelloWorldApp Java program from the command line but either .class file is not there or Java is not able to find the class file due to incorrect classpath settings. The name of the class could be different in each case, it depends upon which class you are passing to java command for running from the command prompt. Another interesting thing to remember is that this error only comes in Java version less than or equal to Java 6 like Java 1.5 or Java 1.4, if you are running in JDK 7 or Java 8 instead of this you will see "Error: could not able to find or load class HelloWorldApp". Technically, both errors come due to some reason and their solution is also exactly the same. --- Java, Unix, Tibco RV and FIX Protocol Tutorial

The java.lang.OutOfMemoryError: GC overhead limit exceeded is another type of OutOfMemoryError in Java which comes when JVM spent too much time doing garbage collection without any success.  For example, if almost 98% of CPU for a Java process is busy doing GC and reclaims very less amount of Java heap space around 2%, then JVM throws "java.lang.OutOfMemoryError: GC overhead limit exceeded" error. Though, the definition of 98% CPU time may vary between different Garbage collectors and different JVM versions.   --- Java, Unix, Tibco RV and FIX Protocol Tutorial

Sometimes we need to create custom Exceptions in Java, i.e. Exceptions which are not defined in JDK or any third-party library your application is using. Though it’s widely recommended on several Exception best practices articles, even Joshua Bloch has recommended in Effective Java to prefer standard exception over custom exception, sometimes you really need it. There are certain guidelines to help to find whether you really need a custom exception or not.  --- Java, Unix, Tibco RV and FIX Protocol Tutorial

You will always see some interview questions from Exception and Error handling in core Java Interviews. Exception handling is an important aspect of Java application development and its key to writing robust, stable Java programs, which makes it natural favorites on interviews. Questions from Error and Exception in Java mostly based on the concept of Exception and Error in Java, How to handle Exception , best practices to follow during Exception handling etc. Though multithreading, garbage collection, JVM concepts and questions from object oriented design rules these interviews, you should always expect and prepare some questions on effective error handling. --- Java, Unix, Tibco RV and FIX Protocol Tutorial

java.net.BindException: Address already in use: JVM_Bind is a common exception in Java with applications trying to connect on a particular port and some other processes either Java or non Java is already connected on that port. You can get "Address already in use: JVM_Bind" error while doing remote debugging in Java in Eclipse, when Eclipse trying to connect to remote Java application when you are starting tomcat and another instance of tomcat is listening on port 8080 you will get java.net.BindException: Address already in use: JVM_Bind:8080. --- Java, Unix, Tibco RV and FIX Protocol Tutorial

You are an enthusiastic Java programmer who just learned about developing Android apps in Java. To start with you have installed Android Studio, which is the official Integrated Development Environment (IDE) for Android app development, based on IntelliJ IDEA, but as soon as you click on the Android Studio Desktop Icon to start Android Studio you are getting "No JVM installation found. Please install a 64-bit JDK" error? How do you solve this problem? Well, even though the error message is the same, every problem is different depending upon your machine, the Java version, whether your desktop or laptop has 32-bit or 64-bit OS e.g. Windows 10 or Windows 11. Whether you have installed 32-bit Java or 64-bit JDK e.g. JDK 21.0 and what is the value of the JAVA_HOME environment variable or whether you have defined it or not. --- Java, Unix, Tibco RV and FIX Protocol Tutorial

Error: Could not find or load main class HelloWorld comes when you are trying to run your Java program using java command with the main class as HelloWorld but Java is not able to find the class. In order to solve this error, you must know how Java find and loads the classes, that's a little bit complex topic for beginners, but we will touch the same base here. For the curious reader, I would suggest reading my post How Classpath works in Java, a must read for a beginner. For now, you just remember that there is an environment variable called CLASSPATH which includes directories where Java looks for all class files and if it doesn't find your main class there then it throws "Error: Could not find or load main class XXX", where XXX is the name of your main class. --- Java, Unix, Tibco RV and FIX Protocol Tutorial

The error ArrayIndexOutOfBoundsException: 1 means index 1 is invalid and it's out of bounding i.e. more than the length of the array. Since the array has a zero-based index in Java, this means you are trying to access the second element of an array which only contains one element. The ArrayIndexOutfBoundsException comes when your code, mostly for loop tries to access an invalid index of the array. If you have worked in C, C++ then you will notice this difference between array in C and Java. You simply cannot access invalid array index in Java i.e. indexes which are less than zero and more than the length of the array. --- Java, Unix, Tibco RV and FIX Protocol Tutorial

If you are working in a Java web or enterprise application that connects to any other web server using HTTPS you might have seen the "javax.net.ssl.SSLHandshakeException". This is one of the particular cases of that error. If you know how SSL and HTTPS work that when a Java client connects to a Java server the SSL handshake happens. In these steps server return certificates to confirm its identity, which the client validates against the root certificate he has in its truststore. If Server returns a certificate that cannot be validated against the certificates a browser or Java client holds in its truststore then it throws the "sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target". --- Java, Unix, Tibco RV and FIX Protocol Tutorial

There are several types of OutOfMemoryError in Java e.g. OutOfMemoryError related to Java heap space and permgen space, and a new one coming in Java 8, Java.lang.OutOfMemoryError: Metaspace. Each and every OutOfMemoryError has its own unique reason and corresponding unique solution. For example, java.langOutOfMemoryError: Java Heap Space comes when the application has exhausted all heap memory and tries to create an object which requires further memory allocation, At that time JVM throws this error to tell the application that it's not possible to create an object. --- Java Interview questions and tutorials

In this blog post of the FIX protocol tutorial series I would like to share my experience with connectivity issues around Fix Engines. to exchange messages or say to trade electronically clients connect to the broker using FIX protocol and for that, they use FIX Engine. In FIX protocol connection between two FIX Engines is refereed as FIX Session and we normally say whether FIX Session is connected or not connected. FIX Session normally has their start time, end time, and EOD time (End of day time) also called TradingSession start time, Trading Session End Time, and Trading Session EOD time. --- Java, Unix, Tibco RV and FIX Protocol Tutorial

The error "java.sql.SQLException: No suitable driver found for jdbc:mysql://localhost:3306/test" occurs when you try to connect MySQL database running on your localhost, listening on port 3306 port from Java program but either you don't have MySQL JDBC driver in your classpath or driver is not registered before calling the getConnection() method. Since JDBC API is part of JDK itself, when you write a Java program to connect any database like MySQL, SQL Server, or Oracle, everything compiles fine, as you only use classes from JDK but at runtime, when the JDBC driver which is required to connect to the database is not available, JDBC API either throws this error or "java.lang.ClassNotFoundException: com.mysql.jdbc.Driver". --- Java, Unix, Tibco RV and FIX Protocol Tutorial

"Failed to connect to queue manager" error comes in WebSphere MQ if any Client like a Java program is not able to connect to the MQ server due to any reason. The reason is actually identified by reason code in error message e.g. code 2397 comes when SSL is enabled between client and server and Java client is not able to connect to the server due to unknown or expired SSL certificates. If you are working in a Java application that is using WebSphere MQ for messaging over SSL then you are bound to face some setup, certificate, and keystore vs truststore related error.  --- Java, Unix, Tibco RV and FIX Protocol Tutorial

Not many Java programmers know that socket connections are treated like files and they use file descriptors, which is a limited resource. The different operating system has different limits on the number of file handles they can manage. One of the common reasons for java.net.SocketException: Too many files open in Tomcat, Weblogic, or any Java application server is, too many clients connecting and disconnecting frequently a very short span of time. Since Socket connection internally uses TCP protocol, which says that a socket can remain in TIME_WAIT state for some time, even after they are closed. One of the reasons to keep the closed socket in the TIME_WAIT state is to ensure that delayed packets reached the corresponding socket. --- Java, Unix, Tibco RV and FIX Protocol Tutorial