Brooke  Giles

Brooke Giles

1604432280

AbstractMethodError in Java

1. Overview

Sometimes, we may encounter AbstractMethodError at runtime in our application. If we don’t know this error well, it might take a while to determine the cause of the problem.

In this tutorial, we’ll take a closer look at AbstractMethodError. We’ll understand what AbstractMethodError is and when it may happen.

2. Introduction to AbstractMethodError

**AbstractMethodError is thrown when an application attempts to call an unimplemented abstract method. **

We know that if there are unimplemented abstract methods, the compiler will complain first. Therefore, the application won’t get built at all.

We may ask how we can get this error at runtime?

First, let’s have a look at where AbstractMethodError fits into the Java exception hierarchy:

java.lang.Object
|_java.lang.Throwable
  |_java.lang.Error
    |_java.lang.LinkageError
      |_java.lang.IncompatibleClassChangeError
        |_java.lang.AbstractMethodError

As the hierarchy above shows, this error is a subclass of IncompatibleClassChangeError. As its parent class’s name implies, AbstractMethodError is usually thrown when incompatibilities exist between compiled classes or JAR files.

Next, let’s understand how this error can happen.

3. How This Error May Happen

When we build an application, usually we’ll import some libraries to make our work easier.

Let’s say, in our application, we include a baeldung-queue library. The baeldung-queue library is a high-level specification library, which contains only one interface:

public interface BaeldungQueue {
    void enqueue(Object o);
    Object dequeue();
}

Also, to use the BaeldungQueue interface, we import a BaeldungQueue implementation library: good-queue. The good-queue library also has only one class:

public class GoodQueue implements BaeldungQueue {
    @Override
    public void enqueue(Object o) {
       //implementation 
    }

    @Override
    public Object dequeue() {
        //implementation 
    }
}

Now, if both good-queue and baeldung-queue are in the classpath, we may create a BaeldungQueue instance in our application:

public class Application {
    BaeldungQueue queue = new GoodQueue();

    public void someMethod(Object element) {
        queue.enqueue(element);
        // ...
        queue.dequeue();
        // ...
    }
}

So far, so good.

Someday, we’ve learned that baeldung-queue released version 2.0 and that it ships with a new method:

public interface BaeldungQueue {
    void enqueue(Object o);
    Object dequeue();

    int size();
}

We want to use the new size() method in our application. Therefore, we upgrade the baeldung-queue library from 1.0 to 2.0. However, we forget to check if there’s a new version of the good-queue library that implements the BaeldungQueue interface changes.

Therefore, we have good-queue 1.0 and baeldung-queue 2.0 in the classpath.

Further, we start using the new method in our application:

public class Application {
    BaeldungQueue queue = new GoodQueue();

    public void someMethod(Object element) {
        // ...
        int size = queue.size(); //<-- AbstractMethodError will be thrown
        // ...
    }
}

Our code will be compiled without any problem.

However, when the line queue.size() is executed at runtime, an AbstractMethodError will be thrown. This is because the good-queue 1.0 library doesn’t implement the method size() in the BaeldungQueue interface.

#java #programming #developer

What is GEEK

Buddha Community

AbstractMethodError in Java
Tyrique  Littel

Tyrique Littel

1600135200

How to Install OpenJDK 11 on CentOS 8

What is OpenJDK?

OpenJDk or Open Java Development Kit is a free, open-source framework of the Java Platform, Standard Edition (or Java SE). It contains the virtual machine, the Java Class Library, and the Java compiler. The difference between the Oracle OpenJDK and Oracle JDK is that OpenJDK is a source code reference point for the open-source model. Simultaneously, the Oracle JDK is a continuation or advanced model of the OpenJDK, which is not open source and requires a license to use.

In this article, we will be installing OpenJDK on Centos 8.

#tutorials #alternatives #centos #centos 8 #configuration #dnf #frameworks #java #java development kit #java ee #java environment variables #java framework #java jdk #java jre #java platform #java sdk #java se #jdk #jre #open java development kit #open source #openjdk #openjdk 11 #openjdk 8 #openjdk runtime environment

Samanta  Moore

Samanta Moore

1620458875

Going Beyond Java 8: Local Variable Type Inference (var) - DZone Java

According to some surveys, such as JetBrains’s great survey, Java 8 is currently the most used version of Java, despite being a 2014 release.

What you are reading is one in a series of articles titled ‘Going beyond Java 8,’ inspired by the contents of my book, Java for Aliens. These articles will guide you step-by-step through the most important features introduced to the language, starting from version 9. The aim is to make you aware of how important it is to move forward from Java 8, explaining the enormous advantages that the latest versions of the language offer.

In this article, we will talk about the most important new feature introduced with Java 10. Officially called local variable type inference, this feature is better known as the **introduction of the word **var. Despite the complicated name, it is actually quite a simple feature to use. However, some observations need to be made before we can see the impact that the introduction of the word var has on other pre-existing characteristics.

#java #java 11 #java 10 #java 12 #var #java 14 #java 13 #java 15 #verbosity

Samanta  Moore

Samanta Moore

1620462686

Spring Boot and Java 16 Records

In this article, we will discuss Java 16’s newest feature, Records. Then we will apply this knowledge and use it in conjunction with a Spring Boot application.

On March 16th, 2021, Java 16 was GA. With this new release, tons of new exciting features have been added. Check out the release notes to know more about these changes in detail. This article’s focus will be on Java Records, which got delivered with JEP 395. Records were first introduced in JDK 14 as a preview feature proposed by JEP 359, and with JDK 15, they remained in preview with JEP 384. However, with JDK 16, Records are no longer in preview.

I have picked Records because they are definitely the most favored feature added in Java 16, according to this Twitter poll by Java Champion Mala Gupta.

I also conducted a similar survey, but it was focused on features from Java 8 onwards. The results were not unexpected, as Java 8 is still widely used. Very unfortunate, though, as tons of new features and improvements are added to newer Java versions. But in terms of features, Java 8 was definitely a game-changer from a developer perspective.

So let’s discuss what the fuss is about Java Records.

#java #springboot #java programming #records #java tutorials #java programmer #java records #java 16

Seamus  Quitzon

Seamus Quitzon

1602637135

Learning by Doing: How to Learn Java Basics by Building Your Own Project

Java is not the hardest language to start with. So, it becomes way popular among novice developers joining the ranks of Java coders every single day. If you are reading this blog post, you might be interested in learning Java.

Java is widely used across industry, and especially in the area of Enterprise software, which results in many high paying job opportunities and makes this programming language a common language for newbies. A general promotion of it within colleges and other institutions providing a formal Computer Science education also contributes to its popularity.

However, these are not the only advantages of Java — among other things, it allows you to adopt good practices and makes it way easier to learn other languages in the future. And with no doubt, you can easily learn it if you’re following the right approach. In this post, I am going to share some of them with you.

The Importance of Practice in Programming

Beyond all doubt, practice is important and valuable. But, before we get to the advantages of hands-on experience, I want to draw your attention to one essential thing I often tell my students.

New programmers who are just learning and start implementing things, without being supervised, often end up adapting bad practices. To avoid that, especially when you are making your first steps in programming, I recommend looking for a person who will supervise you and teach you. A strong mentorship with someone engaged in a serious project, as well as communication within the community in the form of sharing code and asking for feedback, is worth the effort. Similarly, when you are applying for your first job, you want to be looking for a company with a strong team and a good leader who would be keen on investing into your learning.

Now, let’s return to practical experience. Learning by doing is different from learning by passively consuming the information. To make sure we can use all the newly acquired technology, we should put our skills to test and write tons of code. The benefits of hands-on experience are almost endless.

Efficiency and Productivity

By practicing, you get a clear understanding of what programming is. Consequently, you start doing better with each new hands-on task, complete it faster, and thus become more productive.

Even if you are not working on real-world projects yet, it’s important to get used to having deadlines. They are inextricably linked to the programming process. My recommendation is to set up your own deadlines while practicing stage and follow them as closely as possible.

#java #learn java #java code #learn java in easy way #learn java course #learn java development

Samanta  Moore

Samanta Moore

1624948542

Lambda Expression in Java 8

In this blog we will understand what is the lambda expression and why we need lambda expression and how we use lambda and about the functional interface.

What is Lambda Expression :
  • It is an anonymous function.
  • Not having name
  • No return type and no modifiers.

#functional programming #java #functional java #java #java 8 #java8 #lambda expressions in java