我运行时无法找到 Java 中的主类
我有一个java swing代码，其中有5个类，主类引用其他四个类，这里我还添加了一些jar，我给出以下cmd进行编译，
C:\Users\FSSD\Desktop\FinalAttempt\install\lib>javac WriteHelper.java JavaDemo.j
ava DataBaseHelper.java FileEncryption.java SendEmail.java -cp dnsns.jar;dsn.jar
;imap.jar;javaws.jar;jce.jar;jsse.jar;jxl-2.6.jar;localedata.jar;mail.jar;mailap
i.jar;pop3.jar;rt.jar;smtp.jar;sqlitejdbc-v056.jar;sunjce_provider.jar;sunmscapi
.jar;sunpkcs11.jar;tools.jar JavaSamp.java
这里JavaSamp持有主类，其他类是WriteHelper，JavaDemo，DataBaseHelper， fileEncription 和 SendEmail 类，当我使用上面的 cmd 进行编译时，它编译成功，当我运行这个类时，我遇到以下异常
C:\Users\FSSD\Desktop\FinalAttempt\install\lib>java WriteHelper.java JavaDemo.ja
va DataBaseHelper.java FileEncryption.java SendEmail.java -cp dnsns.jar;dsn.jar;
imap.jar;javaws.jar;jce.jar;jsse.jar;jxl-2.6.jar;localedata.jar;mail.jar;mailapi
.jar;pop3.jar;rt.jar;smtp.jar;sqlitejdbc-v056.jar;sunjce_provider.jar;sunmscapi.
jar;sunpkcs11.jar;tools.jar JavaSamp
Exception in thread "main" java.lang.NoClassDefFoundError: WriteHelper/java
Caused by: java.lang.ClassNotFoundException: WriteHelper.java
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Could not find the main class: WriteHelper.java. Program will exit.
我该如何克服它，提前感谢...
I have a java swing code In that There are 5 classes, the Main Class refer other four classes, here i added some jar also, i give the following cmd for compiling,
C:\Users\FSSD\Desktop\FinalAttempt\install\lib>javac WriteHelper.java JavaDemo.j
ava DataBaseHelper.java FileEncryption.java SendEmail.java -cp dnsns.jar;dsn.jar
;imap.jar;javaws.jar;jce.jar;jsse.jar;jxl-2.6.jar;localedata.jar;mail.jar;mailap
i.jar;pop3.jar;rt.jar;smtp.jar;sqlitejdbc-v056.jar;sunjce_provider.jar;sunmscapi
.jar;sunpkcs11.jar;tools.jar JavaSamp.java
Here JavaSamp holding mainclass the other classes are WriteHelper,JavaDemo,DataBaseHelper,fileEncription and SendEmail classes, when i Complied using above cmd it Compiled Successfully, When i run this class i having the following Exception
C:\Users\FSSD\Desktop\FinalAttempt\install\lib>java WriteHelper.java JavaDemo.ja
va DataBaseHelper.java FileEncryption.java SendEmail.java -cp dnsns.jar;dsn.jar;
imap.jar;javaws.jar;jce.jar;jsse.jar;jxl-2.6.jar;localedata.jar;mail.jar;mailapi
.jar;pop3.jar;rt.jar;smtp.jar;sqlitejdbc-v056.jar;sunjce_provider.jar;sunmscapi.
jar;sunpkcs11.jar;tools.jar JavaSamp
Exception in thread "main" java.lang.NoClassDefFoundError: WriteHelper/java
Caused by: java.lang.ClassNotFoundException: WriteHelper.java
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Could not find the main class: WriteHelper.java. Program will exit.
How do i overcome it, thanks in advance...
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您不能通过告诉 Java 类源代码来运行该类。你告诉它运行哪个类。例如：
假设
com.foo包中有一个名为JavaSamp的类。请注意，编译时，您可能应该使用类似-d .的内容来告诉它根据源文件中的包名称将类文件放入以当前目录为根的文件夹结构中。You don't run a Java class by telling it about source code. You tell it which class to run. For example:
That's assuming a class called
JavaSampin a package ofcom.foo. Note that when you compile, you should probably use something like-d .to tell it to put the class files into a folder structure rooted in the current directory, based on the package name within the source file.要运行 java 文件，您需要指定哪个类文件（以
.class扩展名结尾，但不指定扩展名）以及其余的类和库（带有.jar扩展名）在类路径中提供。例如
，要编译该文件，请改用
javac。您所做的就是告诉 java 在WriteHelper目录（或包）中查找java。To run a java file, you specify which class file (ends with a
.classextension but you don't specify the extension) and the rest of the classes and libraries (with a.jarextension) are provided in the classpath.e.g.
To compile the file, use
javacinstead. What you did is you told java to look forjavainWriteHelperdirectory (or package).您需要将第一步生成的类包含到第二步的类路径中。
You need to include the classes generated in the first step to the class path in the second step.
当您运行 java WriteHelper.java 时，您是在告诉 Java 在“WriteHelper”包中查找名为“java”的类。它不存在，这就是异常告诉您的内容：
将类作为
java WriteHelper运行。java命令需要类名...而不是类文件名。编译和运行代码的方式还存在其他问题。
-cp选项及其值必须出现在 Java 源文件名称（对于javac）和 Java 类名称（对于java)。java命令需要一个类名，而不是很多类名。您需要找出具有public static void main(String[] args)方法的类，并（仅）使用该类作为java类参数。 （我猜想，如果您有一个名为Main的类，它具有main入口点方法。）只有在所有类都已声明的情况下，这才有效在默认类中。如果源代码以
package声明开头，则需要将类组织在目录树中，其组件镜像类包；请参阅 @Jon Skeet 的回答。最后，强烈建议您仔细阅读
java和javac的手册页，以及讨论类路径如何工作的链接页面。一旦你理解了它们，这些东西就不再像是黑魔法了。When you run
java WriteHelper.javayou are telling Java to look for a class called "java" in the "WriteHelper" package. It isn't there, and that is what the exception is telling you when it says:Run the class as
java WriteHelper. Thejavacommand expects a class name ... not a class file name.There are other problems with the way that you are compiling and running code.
The
-cpoption and its value must appear before the names of the Java source files (forjavac) and the name of the Java class (forjava).The
javacommand expects ONE class name, not lots of class names. You need to figure out which class is the one with thepublic static void main(String[] args)method and use that one (only) as thejavaclass argument. (I would guess, that if you have a class calledMainthat that has themainentry point method.)This will only work if the classes are all declared in the default class. If the source code starts with a
packagedeclaration, you need to organize the classes in a directory tree whose components mirror the class packages; see @Jon Skeet's answer.Finally, you would be well advised to read the manual pages for
javaandjavaccarefully, along with the linked page that talks about how the classpath works. Once you understand them, this stuff won't seem like black magic anymore.