java命令列下運行class檔案

今天碰到了一個很變態的問題，寫了一個很簡單的HelloWord.java，內容如下：
package com.yanjiuyanjiu;

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

在eclipse中運行是可以的，但是在命令列下運行總是失敗。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   
只有這個成功

Hello
World!

 

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

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"

 

 

 在網上搜尋了大半天，大部分說是環境變數，classpath或JDK版本的問題，還有執行時檔案名稱class尾碼不要。我一一試過，都沒有解決。最後無意中換了一下命令符的位置，成功了。總結如下：

1. 環境變數，CLASSPATH當然要設定好，執行時不要帶class尾碼；

2. 路徑中的斜杠用“/”而不是“/”；

3. 命令符的目前的目錄要在包的起點。比如這裡應該在 d:/workspace/HelloWorld/bin/>，如果在 d:/workspace/HelloWorld/bin/com/yanjiuyanjiu/>，反而不行，有點“近水樓台不得月”的意思，不知道為什麼，還請高手解釋一下。

 

原文地址：http://www.yanjiuyanjiu.com/2011/06/23/javac-mutiple-files/