“找不到主类”
我正在尝试从命令提示符运行示例 Java 应用程序，但出现以下错误：
Exception in thread "main" java.lang.NoClassDefFoundError: com/badlogic/gdx/helloworld/HelloWorldDesktop
Caused by: java.lang.ClassNotFoundException: com.badlogic.gdx.helloworld.HelloWorldDesktop
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Could not find the main class: com.badlogic.gdx.helloworld.HelloWorldDesktop. Program will exit.
我用来尝试运行此应用程序的命令是：
java -cp .;gdx.jar;gdx-backend-jogl.jar com.badlogic.gdx.helloworld.HelloWorldDesktop
所有相关文件都在当前工作目录中 (.java 、.class 和 .jar 文件）
我用来构建 .class 文件的命令如下（有 2 个 .java 文件）：
javac -cp gdx.jar;gdx-backend-jogl.jar HelloWorld.java HelloWorldDesktop.java
同样，这是从同一工作目录运行的 - HelloWorldDesktop.java< 的内容/code> 是（更多或less)：
package com.badlogic.gdx.helloworld;
public class HelloWorldDesktop {
public static void main (String[] argv) {
// Application
}
}
我正在尝试以 C# 开发人员的身份学习 Java，因此虽然我在编程概念方面拥有强大的背景，但整个 java 工具链目前完全让我感到困惑。该异常表明找不到类 HelloWorldDesktop，但据我所知，我已经获得了正确的名称，并且已将正确的 .jar 文件添加到类路径中，所以Java应该能够加载这个类。
为什么找不到HelloWorldDesktop？
I'm trying to run a sample Java application from the command promopt but I'm getting the following error:
Exception in thread "main" java.lang.NoClassDefFoundError: com/badlogic/gdx/helloworld/HelloWorldDesktop
Caused by: java.lang.ClassNotFoundException: com.badlogic.gdx.helloworld.HelloWorldDesktop
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Could not find the main class: com.badlogic.gdx.helloworld.HelloWorldDesktop. Program will exit.
The command I'm using to try and run this app is:
java -cp .;gdx.jar;gdx-backend-jogl.jar com.badlogic.gdx.helloworld.HelloWorldDesktop
Where all relevant files are in the current working directory (.java, .class and .jar files)
The command I used to build the .class files was as follows (there are 2 .java files):
javac -cp gdx.jar;gdx-backend-jogl.jar HelloWorld.java HelloWorldDesktop.java
Again this was run from the same working directory - The contents of HelloWorldDesktop.java is (more or less):
package com.badlogic.gdx.helloworld;
public class HelloWorldDesktop {
public static void main (String[] argv) {
// Application
}
}
I'm attempting to learn Java as a C# developer, so wheras I have a strong background in programming concepts the whole java toolchain is currently completely confusing me. The exception indicates that the class HelloWorldDesktop couldn't be found, but as far as I can tell I've got the correct name and I've added the correct .jar files to the class path and so Java should be able to load this class.
Why can't it find HelloWorldDesktop?
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是的 - 问题是您在当前目录中有
HelloWorldDesktop.class，而它应该在 com/badlogic/gdx/helloworld 中您可以使用 javac 命令修复此问题 - 只需使用
-d .告诉它处理“.”作为输出的包根目录。通常您还希望按包组织源代码，但对于这个“hello world”测试来说可能不值得。
Right - the problem is that you've got
HelloWorldDesktop.classin the current directory, whereas it should be in com/badlogic/gdx/helloworldYou can fix this with the javac command - just use
-d .to tell it to treat "." as the package root directory for output.Normally you would want to also organize your source code by package, but for this "hello world" test it may not be worth it.
好的，首先您需要使用两个不同的工具编译并运行应用程序
第 1 步：javac.exe，它将 .java 文件编译为 .class 文件。
示例：javac.exe ProgramFolder\*.java（其中 ProgramFolder = 文件系统目录）
然后
步骤 2：java.exe 并给出要运行的应用程序（包括路径）作为参数，但不要对文件夹使用“\”，而使用“ ”。以及你班级的名字
示例：ProgramFolder.ClassProgram
可以。如果您尝试运行 Java.exe ProgramFolder\Program.class 或仅 ProgramFolder\Program 或进入类文件所在的文件夹并且仅执行 Java.exe Program.class，它将始终给您找不到主类错误。
看看这张图片的前两行 http://3.bp.blogspot.com/-FO4Hmg9LrI0/Td7FoSIi_XI/AAAAAAAAF6g/FVAiP0h8CSc/s1600/fiborial_java.PNG
Ok, first of all you need to compile and then run the app using two different tools
Step 1: javac.exe which compiles the .java files into .class files.
Example: javac.exe ProgramFolder\*.java (where ProgramFolder = File System Directory)
then
Step 2: java.exe and give as parameter the app you want to run including the path, but instead of using "\" for folders use "." and the name of your class
Example: ProgramFolder.ClassProgram
That will work. if you try to run Java.exe ProgramFolder\Program.class or just ProgramFolder\Program or go into the folder where the class files are and only do Java.exe Program.class it will always give you the cannot find Main class error.
Have a look at the first 2 lines of this picture http://3.bp.blogspot.com/-FO4Hmg9LrI0/Td7FoSIi_XI/AAAAAAAAF6g/FVAiP0h8CSc/s1600/fiborial_java.PNG