Java Summary, Error set

How to use abstract in Java

Abstract modifiers, which can be decorated with classes and methods 1,abstract decorated classes, make this class an abstract class that cannot generate object instances, but can be used as the type of object variable declaration, that is, the compile-time type, which is like a class of semi-finished products, An abstract method that requires subclasses to inherit and overwrite. The 2,abstract modification method makes this method an abstract method, that is, only the declaration (definition) is not implemented, and the implementation part is replaced with ";". Subclass inheritance Implementation (overwrite) is required. Note: Classes with abstract methods must be abstract classes. But abstract classes are not necessarily abstract methods, but they can all be concrete methods. The abstract modifier must be placed before the class name when decorating the class. The abstract modification method is to require its subclasses to overwrite (implement) this method. Calls can be called in a polymorphic way after a subclass overrides (implements) the method, which means that the abstract method must be implemented in its subclasses, unless the subclass itself is an abstract class. Note: The parent class is an abstract class, in which there is an abstract method, then the subclass inherits the parent class and implements (overwrites) all the abstract methods in the parent class, and the subclass has the ability to create an instance of the object, or the subclass must be an abstract class. An abstract class can have a constructor method, which is the constructor of the parent class (abstract class) that the subclass needs to call when constructing the subclass object. To give a simple example, there is an abstract class, e{public  abstract  void  Show ();//public abstract can be omitted} Then other classes if inheriting it usually in order to implement it inside the method class F extends e{     void Show () {    

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Webexample call the Web jar, after modifying the Web source code, the Web execution install,webexample executes the Run application.


Eclipse Error Set
Always update >>>> (also welcome to the problems and solutions you encounter to share, so that we can less detours)
1. Abnormal phenomenon: "Software Update" appears: Error retrieving "Feature.xml". [Error in opening zip file]
Workaround: Delete the site.xml under Eclipse root
2, abnormal phenomenon: appears log4j:error a "Org.jboss.logging.util.OnlyOnceErrorHandler" object is not assignable to A " Org.apache.log4j.spi.ErrorHandler "Variable's exception
Workaround: Change the following two properties in/server/default/jbossweb-tomcat55.sar/meta-inf/jboss-service.xml to True
True
True
3, abnormal phenomenon: The class file Collision:a resource exists with A different case:/test/testframe$myactionlistener.class.
Cause: File name case problem is caused.
Workaround:
1. Delete the files in the directory first
2, remove project->build automatically before the tick
3. Select Project->clean
4, check project->build automatically, recompile
If the above execution is not resolved, select Project->properities, delete all history in refactoring and perform the above steps
4. Exception: Eclipse hint: Problem calling code from plug-in: "Org.eclipse.jface" exception
Workaround: Delete the workspace and re-establish the new Wordspace
5. Abnormal phenomenon: Prompt java.lang.UnsatisfiedLinkError:no swt-win32-3232 in Java.library.path when developing interface with SWT
Solution: Need to Eclipse\plugins\org.eclipse.swt.win32.win32.x86_3.2.0.v3232m.jar inside the swt-win32-3232.dll extracted to copy to Windows\ SYSTEM32 inside.

No compiler isProvidedinch  ThisEnvironment. Perhaps is running on a JRE rather than a JDK?The problem Maven compiles the project with an error, prompting the following message: [ERROR] No compiler isProvidedinch  ThisEnvironment. Perhaps is running on a JRE rather than a JDK?[ERROR]--[Help1][error][error] To see the full stack trace of the errors, re-run Maven with The-eSwitch. [ERROR] Re-run MavenusingThe-xSwitchTo enable full debug logging. [ERROR] [ERROR] For more information on the errors and possible solutions, please read the following articles: solution: Download Java JDK and Install the Java JDK. : http://www.oracle.com/technetwork/java/javase/downloads/jdk7-downloads-1880260.htmlFrom the Eclipse menu, go to Window > Preferences > Java > Installed jres > Execution environments, select javase-1.7, on the right side add or edit jdk. Then use "Update Project ..." In the Maven menu .

Could not write File:c:\......\.classpathfilecwindowsbuildlinuxpath ' Setting Build Path '  from areset This attribute fixes the error. Right-click the. classpath file to cancel the "hide" 

Java Summary, Error set