当我在 Linux 中从命令行运行 Java 类文件时，为什么会收到 NoClassDefFoundError 错误？

发布于 2024-11-29 10:27:42 字数 1150 浏览 1 评论 0原文

我正在尝试从 Linux 命令行运行 test.class 文件。我使用 javac test.java 编译了该文件，生成了 test.class 文件。当我运行命令 java test 时，它会抛出一个类未找到异常。我也尝试指定包名称，结果相同。这是输出，有人可以帮忙吗？根据谷歌搜索，我相信我的语法是正确的。

[root@localhost usr]# java test
Exception in thread "main" java.lang.NoClassDefFoundError: test (wrong name: testJava/test)
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:634)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:277)
        at java.net.URLClassLoader.access$000(URLClassLoader.java:73)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:212)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
Could not find the main class: test. Program will exit.

原文

I am trying to run a test.class file from the linux command line. I compiled the file using javac test.java which produced the test.class file. When I run the command java test it throws a class not found exception. I also tried specifying the package name with the same result. Here is the output, can anybody help? I believe my syntax is correct according to Google searches.

[root@localhost usr]# java test
Exception in thread "main" java.lang.NoClassDefFoundError: test (wrong name: testJava/test)
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:634)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:277)
        at java.net.URLClassLoader.access$000(URLClassLoader.java:73)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:212)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
Could not find the main class: test. Program will exit.

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死开点丶别碍眼 2024-12-06 10:27:42

您需要使用 javac 编译您的 .java 文件：

  javac MyFile.java

然后使用 java 运行该文件

  java MyFile

如果您执行此操作但仍然不起作用，则意味着您需要确保该文件和文件内的类名具有相同的名称名称...所以 MyFile.java 包含

  class MyFile
  {
     // ...
     public static void main(String[] args)
     {
        // ...
     }
     // ...
  }

You need to compile your .java file with javac:

  javac MyFile.java

Then run the file using java

  java MyFile

If you're doing this and it still doesn't work, that means you need to make sure the file and the class name inside the file have the same name... so MyFile.java contains

  class MyFile
  {
     // ...
     public static void main(String[] args)
     {
        // ...
     }
     // ...
  }

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廻憶裏菂餘溫 2024-12-06 10:27:42

使用
testJava 父目录中的 java testJava.test

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娇纵 2024-12-06 10:27:42

假设您的类如下所示：

package javaTest;

public class test{
    public static void main(String[] a){
        System.out.println("Test");
    }
}

然后要编译并运行该文件，您基本上会这样做：

$ ls
testJava
$ ls testJava
test.java
$ javac testJava/test.java
$ java testJava.test
Test

这意味着您必须使用其完全限定名称运行该类，其中包括该类的包名称。您还必须从包含包根目录的目录执行此操作。（除非您使用 -cp 标志指定“根”目录。）

Assuming your class looks like this:

package javaTest;

public class test{
    public static void main(String[] a){
        System.out.println("Test");
    }
}

Then to compile and run the file, you basically do this:

$ ls
testJava
$ ls testJava
test.java
$ javac testJava/test.java
$ java testJava.test
Test

What this means is that you have to run the class with its fully qualified name, which includes the package name of the class.You also have to do it from the directory that conatins the root of your package. (Unless you specify the "root" directory with the -cp flag.)

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