今天碰到了一個(gè)很變態(tài)的問(wèn)題，寫(xiě)了一個(gè)很簡(jiǎn)單的HelloWord.java，內(nèi)容如下：

package com.yanjiuyanjiu;

public class HelloWorld {

public static void main(String args[]) {

System.out.println("Hello World!");

}

}

在eclipse中運(yùn)行是可以的，但是在命令行下運(yùn)行總是失敗。我的工程位置為 d:/workspace/HelloWorld/。

嘗試了很多次，如下

d:/workspace/HelloWorld/bin/com/yanjiuyanjiu/>java HelloWorld

Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld (wrong name: com/yanjiuyanjiu/HelloWorld)

at java.lang.ClassLoader.defineClass1(Native Method)

at java.lang.ClassLoader.defineClassCond(Unknown Source)

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$000(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)

Could not find the main class: HelloWorld.? Program will exit.

Exception in thread "main"

d:/workspace/HelloWorld/bin/com/yanjiuyanjiu/>java -classpath .; HelloWorld

Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld (wrong name: com/yanjiuyanjiu/HelloWorld)

at java.lang.ClassLoader.defineClass1(Native Method)

at java.lang.ClassLoader.defineClassCond(Unknown Source)

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$000(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)

Could not find the main class: HelloWorld.? Program will exit.

Exception in thread "main"

d:/workspace/HelloWorld/bin/com/yanjiuyanjiu/>cd..

d:/workspace/HelloWorld/bin/com/>cd..

d:/workspace/HelloWorld/bin/>java -classpath .; com/yanjiuyanjiu/HelloWorld只有這個(gè)成功

Hello World!

d:/workspace/HelloWorld/bin/>java -classpath .; com/yanjiuyanjiu/HelloWorld換了個(gè)斜杠就不行了

Exception in thread "main" java.lang.NoClassDefFoundError: com/yanjiuyanjiu/HelloWorld (wrong name: com/yanjiuyanjiu/HelloWorld)

at java.lang.ClassLoader.defineClass1(Native Method)

at java.lang.ClassLoader.defineClassCond(Unknown Source)

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$000(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)

Could not find the main class: com/yanjiuyanjiu/HelloWorld.? Program will exit.

Exception in thread "main"

d:/workspace/HelloWorld/bin/>java -classpath ./com/yanjiuyanjiu/; HelloWorld

Exception in thread "main"java.lang.NoClassDefFoundError: HelloWorld (wrong name: com/yanjiuyanjiu/HelloWorld)

at java.lang.ClassLoader.defineClass1(Native Method)

at java.lang.ClassLoader.defineClassCond(Unknown Source)

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$000(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)

Could not find the main class: HelloWorld.? Program will exit.

Exception in thread "main"

在網(wǎng)上搜索了大半天，大部分說(shuō)是環(huán)境變量，classpath或JDK版本的問(wèn)題，還有執(zhí)行時(shí)文件名class后綴不要。我一一試過(guò)，都沒(méi)有解決。最后無(wú)意中換了一下命令符的位置，成功了?？偨Y(jié)如下：

1. 環(huán)境變量，CLASSPATH當(dāng)然要設(shè)置好，執(zhí)行時(shí)不要帶class后綴；

2. 路徑中的斜杠用“/”而不是“/”；

3. 命令符的當(dāng)前目錄要在包的起點(diǎn)。比如這里應(yīng)該在 d:/workspace/HelloWorld/bin/>，如果在 d:/workspace/HelloWorld/bin/com/yanjiuyanjiu/>，反而不行，有點(diǎn)“近水樓臺(tái)不得月”的意思，不知道為什么，還請(qǐng)高手解釋一下。

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