如何从 cmd 运行作为包一部分的 .class 文件?

2022-01-13 00:00:00 class package cmd java javac

当我将 .class 作为 package 的一部分并尝试从 cmd 运行它时，我不断收到错误.

I keep getting errors when I make my .class part of a package and try to run it from cmd.

这是使用 javac 然后使用 java:

Here's the code that works after using javac and then java:

class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}

然后是不起作用的代码:

and then the code that does not work:

package com;

class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}

尝试通过以下命令运行程序后出现此错误:java HelloWorld:

giving me this error after trying to run the program via the command: java HelloWorld:

Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld (wrong nam
e: com/HelloWorld)
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(Unknown Source)
    at java.security.SecureClassLoader.defineClass(Unknown Source)
    at java.net.URLClassLoader.defineClass(Unknown Source)
    at java.net.URLClassLoader.access$100(Unknown Source)
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.launcher.LauncherHelper.checkAndLoadMain(Unknown Source)

这是我迄今为止尝试过的:

Here's what I've tried doing so far:

java -cp . HelloWorld
java -cp . com.HelloWorld
java -cp . com/HelloWorld
java HelloWorld
java com.HelloWorld
java com/HelloWorld

请记住，javac 返回时没有错误，只需删除 package com; 即可解决问题.有时在其他情况下，我会收到一条错误消息，提示找不到主类文件或类似的内容.

Keep in mind that javac returns with no errors and that simply removing package com; solves the problem. Sometimes in other scenarios I get an error that says the main class file cannot be found or something along those lines.

我做错了什么?

推荐答案

假设你做了 cd C:/projects 并且 HelloWorld.class 在 C:/projects/com，然后输入:

Suppose you did cd C:/projects and HelloWorld.class is in C:/projects/com, then just type:

java com.HelloWorld

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