- java.lang.AbstractMethodError – How to resolve Abstract Method Error
- The structure of AbstractMethodError
- The AbstractMethodError in Java
- More about the AbstractMethodError in Java
- How to deal with AbstractMethodError
- About The Error
- Why It Occurs?
- How Do You Fix Java.lang.AbstractMethodError?
- Find More Support At Codexoxo – Contact
- Resolve Missing Method Body or Declare Abstract in Java
- Resolve the Missing Method Body or Declare Abstract Error in Java
- Related Article — Java Error
- Class Is Not Abstract and Does Not Override Error in Java
- Why Does the Error Class is not abstract and does not override abstract method Occur in Java?
- Solution 1: Override the canSpeak() Method
- Solution 2: Make Baby Abstract
- Solution 3: Make Human a Class and Extend It in the Baby Class
- Related Article — Java Error
- Related Article — Java Class
java.lang.AbstractMethodError – How to resolve Abstract Method Error
In this example we will discuss about AbstractMethodError . As you may have figured out, this is thrown when the application calls an abstract method. Normally, this error is caught by the compiler, it can only occur at run time if the definition of some class has incompatibly changed since the currently executing method was last compiled. The AbstractMethodError extends the IncompatibleClassChangeError class, which occurs when an incompatible class change has occurred to some class definition. The AbstractMethodError exists since JDK 1.0.
The structure of AbstractMethodError
The AbstractMethodError in Java
To make an example of AbstractMethodError , I will use the javac compiler from the command-line. This error is thrown when the classes are separately-compiled, and most of IDEs don’t allow this.
Create a java class called AbsClass with the following source code:
To compile this class, execute this on the command-line:
Now that the first class is compiled, create the second class, called MainClass , with this source code:
public class MainClass extends AbsClass < public static void main(String[] args) < MainClass obj = new MainClass(); obj.hello(); >>
The output of compiling and running this would be:
>_ javac MainClass.java >_ java MainClass Hello! I belong to AbsClass
Things are actually OK, but what would happen if we change the hello() method to abstract and then recompile AbsClass without changing MainClass ? Let’s try it, by changing AbsClass to this:
public abstract class AbsClass
Now, I can recompile this class without any problem, but when I run the MainClass , I get this:
>_ java MainClass Exception in thread "main" java.lang.AbstractMethodError: MainClass.hello()V at MainClass.main(MainClass.java:6)
More about the AbstractMethodError in Java
AbstractMethodError is thrown when the programmer calls an abstract method without firstly overriding it. Of course, this would resolve in a compile-time error and the compilation would fail, but it doesn’t always go this way.
AbstractMethodError would happen if a method of the base class changes to abstract, hence changing the base class to abstract, and all this happens without the proper changes in the child class (i.e. overriding the abstract methods). So, just as in the example above, the programmer calls an abstract, not implemented method (without knowledge of its abstractness), and he is not informed of this error since only the base class gets changed and compiled.
How to deal with AbstractMethodError
What you need to do in this case, is just implement the abstract method of the AbsClass in the MainClass . This would solve the problem you have with the AbstractMethodError .
About The Error
Getting an error such as “java.lang.AbstractMethodError” may not be a common one though.
In Java programming, an ‘Abstract Method’ is a method which is declared without showing implementation details, except the function that a programmer can actually carry out. Also, it only has a method signature, but no method body.
Generally, this type of error is thrown at run-time when an abstract method cannot be invoked in the program. Beginners who are new in Java programming, may experience such error, especially when using the abstract method or abstract class.
Why It Occurs?
There can be various reasons that cause this error in a Java program or application. One of the reasons is that the java.lang.AbstractMethodError occurs when an application attempts to call an abstract method in a Java program. Most of the time, this type of abstract method error is caught by the compiler before it is executed. So, if you have written a Java program using abstract classes and abstract methods and have encountered the java.lang.AbstractMethodError during code compilation, then this could be the main reason for the occurrence of the error in your Java program.
Other reason which leads to the occurrence of java.lang.abstractmethoderror in a Java program may be due to what is called binary incompatibility. Here, binary refers to any data that is invoked in a Java program, usually by the abstract method or abstract class. In an abstract class, the sub-class has to have an implementation for only the methods marked as abstract.
Most beginners as well as professional programmers use a Java application such as Eclipse or NetBeans for compiling and executing their code. Thus, if you fail to declare a class using the abstract keyword, your chances of encountering the issue will eventually increase.
How Do You Fix Java.lang.AbstractMethodError?
What basically happens here is that whenever a class is modified, then the other classes that refer to the modified class will not be aware of the changes which have been made by the previous class. Therefore, in order to avoid this type of error in Java, it is a good idea to compile all classes as a whole.
Getting the Java.lang.AbstractMethodError in Java can be resolved quickly with the help of a couple of effective solutions. If you are not familiar with java.lang.abstractmethoderror in Java programming, you might not be able to find the right solution through which you can fix the error with less effort.
Find More Support At Codexoxo – Contact
The solutions given above will help you resolve the “Java.lang.AbstractMethodError” error in Java easily and quickly. Apart from the solutions given above, if you are still experiencing problems, or are getting other errors and issues with regards to Java programming, you can contact us to avail assistance from our Java experts at Codexoxo. Our support centre can be reached by dialling the toll-free phone number round the clock.
Speak with our team of Java professionals today and get help immediately to resolve any issues and errors which you encounter in Java. Our experts can assist and guide you with tasks such as Java programming, developing websites and applications for desktop as well as mobile platform and much more.
Resolve Missing Method Body or Declare Abstract in Java
This tutorial discusses a compile-time error, missing method body, or declare abstract . Here, we will go through three different steps.
First, we will understand a Java program to learn about the error. Second, highlight the possible causes of this error and finally have a solution to eradicate this compile time error.
Resolve the Missing Method Body or Declare Abstract Error in Java
Let’s start with the first step and understand the program causing this error.
Example Code ( Main.java class):
class Main public static void main(String[] param) HiWorld(); System.exit(0); > public static void HiWorld(); System.out.println("Hi World"); > > Here, we have a Main.java class that contains a main() method. Inside the main() method, we call a method HiWorld() and exit from the program.
Then, the HiWorld method has a simple println statement.
Everything seems fine, but this is causing the error saying missing method body, or declare abstract . Why? It is because the compiler assumes that we have missed writing the function body or we want to declare this function as abstract , but we forgot to write the abstract keyword while defining the function.
Here, we are at the second step to learn about possible reasons causing this error. All possible reasons are listed below:
- First, re-check the code. We might have put the semi-colon ( ; ) at the end of the function definition or somewhere else where it should not be. If so, remove that.
- Another possibility is to forget to write the abstract keyword if we were intended to write an abstract method.
- Sometimes, we get this error if we have forgotten the < after the main() method.
- If you have setters in your program, then make sure the setters are not returning any value because usually, they do not have the return type.
In our case, we have written the semi-colon ( ; ) at the end of the HiWorld() method’s definition. So, removing it leads to the final step, which is a solution for this error.
class Main public static void main(String[] param) HiWorld(); System.exit(0); > public static void HiWorld() System.out.println("Hi World"); > > Mehvish Ashiq is a former Java Programmer and a Data Science enthusiast who leverages her expertise to help others to learn and grow by creating interesting, useful, and reader-friendly content in Computer Programming, Data Science, and Technology.
Related Article — Java Error
Class Is Not Abstract and Does Not Override Error in Java
- Why Does the Error Class is not abstract and does not override abstract method Occur in Java?
- Solution 1: Override the canSpeak() Method
- Solution 2: Make Baby Abstract
- Solution 3: Make Human a Class and Extend It in the Baby Class
This article will find solutions to the error Class is not abstract and does not override abstract method that occurs when we use the concept of abstraction in Java.
Why Does the Error Class is not abstract and does not override abstract method Occur in Java?
In the code below, we have two classes and an interface. The class JavaExample has a main() method without any body part. We create a Human interface with an abstract method canSpeak() with boolean as a return type. We do not specify a body for canSpeak() because an abstract method doesn’t have a body.
In the second class, Baby , we inherit the Human interface using the implements keyword. If we use an IDE, there will be an error, and when we run the code, the error will occur, as shown in the output.
If we look at the error Baby is not abstract and does not override abstract method canSpeak() in Human , we can understand why it occurred. It says that the class Baby is not abstract, and it doesn’t override the method canSpeak() of the Human interface.
This error appears because we have to override the abstract methods to define the body when implementing any class interface with abstract methods.
public class JavaExample public static void main(String[] args) > > class Baby implements Human > interface Human abstract boolean canSpeak(); > java: Baby is not abstract and does not override abstract method speak() in Human Solution 1: Override the canSpeak() Method
To fix the Baby is not abstract and does not override abstract method speak() in Human error, the first solution is to override the abstract method canSpeak() in the Baby class that implements the Human interface.
The canSpeak() function returns false and in the main() method we create an object of the Baby class and call the overridden function canSpeak() . In the output, we can see that there’s no error, and the expected value shows.
public class JavaExample public static void main(String[] args) Baby baby = new Baby(); System.out.println("Can Speak? "+baby.canSpeak()); > > class Baby implements Human @Override public boolean canSpeak() return false; > > interface Human abstract boolean canSpeak(); > Solution 2: Make Baby Abstract
Another solution involves making the class Baby an abstract . We have the same code here, but Baby is an abstract class. It cannot be initialized; we only create an instance of the Baby class in the main() method.
public class JavaExample public static void main(String[] args) Baby baby; > > abstract class Baby implements Human > interface Human abstract boolean canSpeak(); > Solution 3: Make Human a Class and Extend It in the Baby Class
The last solution is a different one. Instead of implementing an interface, we can change the interface Human to a class and extend that class in the Baby class using the keyword extends . We specify the body of canSpeak() in the Human class itself, which removes the error.
public class JavaExample public static void main(String[] args) Baby baby = new Baby(); System.out.println("Can Speak? " + baby.canSpeak()); > > class Baby extends Human > class Human boolean canSpeak() return false; > > Rupam Saini is an android developer, who also works sometimes as a web developer., He likes to read books and write about various things.
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Related Article — Java Class
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