error java lang nullpointerexception unexpected error

Exception and error difference error and Exception Learn the difference between the exception and the error, and know what to do when you intercept an exception. by Josh Street Many programmers do not realize that there is a difference between an error and an exception, and that this distinction has important impli

interviewing technical managers. Because exception handling is critical in project design, it is essential to be proficient in exception handling. There are many best practices for exception handling, which are listed below, which improve the robustness and flexibility of your code: 1 Returns a Boolean value when invoking the method instead of returning null, which can be nullpointerexception. Because the null pointer is the most disgusting exception

handle. The Exception class has an important subclass runtimeexception. The RuntimeException class and its subclasses represent errors thrown by the JVM common Operation . For example, if you attempt to use null object references, divide by zero, or array out of bounds, the run-time exceptions (NullPointerException, ArithmeticException), and arrayindexoutofboundexception are raised respectively.Note: Exceptions and errors are different: Exceptions ca

, try-catch Block Processing, or add throws to the method to throw the exception to the upper layer of the call stack. Inherited from java. lang. Exception (except java. lang. RuntimeException ). Unchecked exception: Indicates the program logic error. Is a subclass of Runtim

accessed, nullpointerexception is thrown. Another scenario is that Java allows programmers to extend this semantic check. programmers can create their own exceptions and choose when to use the throw keyword to cause exceptions. All exceptions are subclasses of Java. Lang. thowable.Eg: First TypeClass test {Public int

critical in project design, it is necessary to be proficient in exception handling. There are a number of best practices for exception handling, as outlined below, which improve the robustness and flexibility of your code:1) Returns a Boolean value when invoking a method instead of returning null, which can be nullpointerexception. Since the null pointer is the most disgusting exception in Java exceptions,

array is created, each reference is automatically set as a special value. This value is expressed by the keyword null. When Java sees the null value, it regards this reference as "not pointing to any object ". Before using any reference, you must assign an object to it. If you use a reference and its value is null, an error will occur during the execution period.Array initialization starts when space is al

A project was downloaded from the Web, and the following error was found when importing eclipse:Check that the original JDK version is inconsistent, the project's default JDK configuration is 1.5, and on its own computer is 1.7.You need to modify the configuration of two places as shown in:Modify One:Modified two:After modifying these two places, you can!Reference:(1) http://blog.sina.com.cn/s/blog_87479ba60100x6wh.html(2) http://blog.csdn.net/chszs/a

Java basic questions: What are the similarities and differences between runtime exceptions and general exceptions? What is the difference between error and exception? Please write the five most common runtimeexception ?, ThrowableIt is the parent class for Java Error handling. It has two subclasses:

most essential difference between exceptions and errors is that exceptions can be handled by developers. When errors occur, the system comes with them. Generally, they cannot be handled and do not need to be handled by our programmers.1. An exception is an event that occurs during the execution of a program. It interrupts the running of normal commands.2. Error. An action or instance that deviates from an acceptable code behaviorException Structure c

One, error dynamic Web Module 3.0 requires Java 1.6 or newerWorkaround, add the Java version of the property configuration to the Pom.xml file as followsNote that the configuration needs to be added to the Ii. error cannot change version of the project facet Dynamic Web Module to 3.0This

().toString();File file = new File(appDir + "/" + "config.properties");if(!file.exists()){ file.createNewFile();} Use getApplicationContext (). getFilesDir (). toString () to obtain the absolute path of the application package directory, and then create a file. The absolute path is "/data/com. company. App/files/", and com. company. App indicates your application package name. Error 2 Java.

The error message is as follows:The class file HashmapThe solutions that are given online are:"This problem arises because it is compiled under different JDK versions and can be resolved as follows:Add JDK 1.7 under window-preferenecs-java-installed jres (if available);Right-click Project-properties-java build Path-libraries-add LIBRARY-JRE System library point N

If you encounter an error when tomcat is started in the Java Web project 14:39:32, 657 INFO (org. springframework. web. context. ContextLoader: 296)-Root WebApplicationContext: initialization completed in 3735 MS14:39:32, 740 INFO (com. opensymphony. xwork2.config. providers. XmlConfiGurationProvider: 42)-Parsing configuration file [struts-default.xml]14:39:44, 805 ERRO