Abstract Error Java
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Method java.lang Class AbstractMethodError
Missing Method Body Or Declare Abstract Error Java
java.lang.Object java.lang.Throwable java.lang.Error java.lang.LinkageError java.lang.IncompatibleClassChangeError java.lang.AbstractMethodError All Implemented Interfaces: java.lang.abstractmethoderror android Serializable public class AbstractMethodError extends IncompatibleClassChangeError Thrown when an application tries to call an abstract
Java.lang.abstractmethoderror Spring
method. Normally, this error is caught by the compiler; this error can only occur at run time if the definition of some class has incompatibly changed since the currently java.lang.abstractmethoderror hibernate executing method was last compiled. Since: JDK1.0 See Also:Serialized Form Constructor Summary Constructors Constructor and Description AbstractMethodError() Constructs an AbstractMethodError with no detail message. AbstractMethodError(Strings) Constructs an AbstractMethodError with the specified detail message. Method Summary Methods inherited from classjava.lang.Throwable addSuppressed, fillInStackTrace, getCause, getLocalizedMessage, getMessage, getStackTrace, getSuppressed, initCause, printStackTrace, printStackTrace, printStackTrace, setStackTrace, toString Methods inherited from classjava.lang.Object clone, equals, finalize, getClass, hashCode, Java.lang.abstractmethoderror Javax.ws.rs.core.uribuilder.uri(ljava/lang/string ) Learn more about Stack Overflow the company Business Learn more about hiring developers or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow connection isvalid abstractmethoderror Community Stack Overflow is a community of 4.7 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up Abstract Class Error in Java up vote 0 https://docs.oracle.com/javase/7/docs/api/java/lang/AbstractMethodError.html down vote favorite I'm new to Java and I'm running into a compile error I cannot figure out. Chapter5Debug is not abstract and does not override abstract method itemStateChanged(java.awt.event.ItemEvent) in java.awt.event.ItemListener public class Chapter5Debug extends Frame implements ItemListener ^ Can anyone help me understand what I need to do to fix this? Appreciate the help! Sheila abstract share|improve this question edited Jul 23 '13 at 2:55 SheetJS 12k63755 http://stackoverflow.com/questions/17800659/abstract-class-error-in-java asked Jul 23 '13 at 2:47 Sheila Mathews 94 add a comment| 4 Answers 4 active oldest votes up vote 1 down vote accepted You have to remember that if ItemListener is abstract, then you will need to implement all the methods inside ItemListener. If you want to keep your current structure, you can just add an empty itemStateChanged method to your Chapter5Debug class. share|improve this answer answered Jul 23 '13 at 2:53 kevolution 513 add a comment| up vote 1 down vote To elaborate on @kevolution's answer: public class Chapter5Debug extends Frame implements ItemListener { public void itemStateChanged(ItemEvent e) { // Write your method here } } An abstract class is one which is just like a regular class but can contain some 'stub' - or abstract - methods. These are methods which need to be implemented by the class extending the abstract class. In this case, itemStateChanged() is marked as abstract, meaning that you need to declare it. Abstract classes are useful for when you're writing code which you need the caller to provide guts in some ways. In this case, Java cannot know what to do when the item's state changes, but it can do a whole method cannot be invoked and if we try to do so then you will get a compile-time error.So you may think how this error is thrown at run-time?. The reason http://craftingjava.blogspot.com/2012/07/javalangabstractmethoderror.html is binary incompatibility-what does it mean? Whenever a http://beginnersbook.com/2013/05/java-abstract-class-method/ class is modified,other classes that refer to this (modified) class will not be aware of the changes made in it.So all the classes must be compiled as a whole.If not then you may encounter one of the subclasses of incompatible class change error. "This error indicates that the method error java that you invoke is converted into an abstract method now". see the following example to have an idea about this error class B { public void display() { System.out.println("I am inside B"); } } import java.util.*; public class A extends B { public static void main(String args[]) { A a=new A(); a.display(); } } output: C:\blog>javac A.java C:\blog>java A I am abstract error java inside B Now i am going to convert the display()method as an abstract method and compile it alone. abstract class B { public abstract void display(); } Output: C:\blog>javac A.java C:\blog>java A I am inside B C:\blog>javac B.java C:\blog>java A Exception in thread "main" java.lang.AbstractMethodError: B.display()V at A.display(A.java:3) at A.main(A.java:8) As you see,the reason for this exception to be thrown at run-time is i have not compiled the classes as a whole.So whenever you make changes to the existing classes ensure that you have compiled the classes as a whole. Hence it is not a good practice to change a method into an abstract method in classes that are distributed.Mostly these kind of error occurs when you use third party library in your application. If this error is not shown at compile time,even if you compile it as a whole package then you must have to check your library settings and class path settings. Because compiler usually searches for classes in system libraries like bootstrap libraries and extension libraries,also in the current directory,but ConceptA class that is declared using "abstract" keyword is known as abstract class. It may or may not include abstract methods which means in abstract class you can have concrete methods (methods with body) as well along with abstract methods ( without an implementation, without braces, and followed by a semicolon). An abstract class can not be instantiated (you are not allowed to create object of Abstract class). Abstract class declaration Specifying abstract keyword before the class during declaration, makes it abstract. Have a look at below code: // Declaration using abstract keyword abstract class AbstractDemo{ // Concrete method: body and braces public void myMethod(){ //Statements here } // Abstract method: without body and braces abstract public void anotherMethod(); } Since abstract class allows concrete methods as well, it does not provide 100% abstraction. You can say that it provides partial abstraction. Interfaces are used for 100% abstraction (full abstraction) Remember two rules: 1) If the class is having few abstract methods and few concrete methods: declare it as abstract class. 2) If the class is having only abstract methods: declare it as interface. Error!! - Object creation of abstract class is not allowed As discussed above, we cannot instantiate an abstract class. The following code throws an error. abstract public class AbstractDemo{ public void myMethod(){ System.out.println("Hello"); } abstract public void anotherMethod(); } public class ConcreteDemo{ public void anotherMethod() { System.out.print("Abstract method"); } public static void main(String args[]) { //Can't create object of abstract class - error! AbstractDemo obj = new AbstractDemo(); obj.display(); } } Output: Unresolved compilation problem: Cannot instantiate the type AbstractEx1 Note: The class that extends the abstract class, have to implement all the abstract methods of abstract class, else they can be declared abstract in the class as well. Why we need an abstract class? Let me explain this with an example. Suppose there is a class Animal and there are few other classes like Cat, Dog and Horse. These classes extends Animal class so basically they are having few common habits(methods in technically) which they are inheriting from Animal class. Now, if you have understood the above example then you would have been able to figure out that creating object of Animal class has no significance as you can't judge that the new object of Animal class will represent which animal. Hence for such kind of scenarios we generally creates an abstract class and later coJava.lang.abstractmethoderror: Abstract Method