Question

我已经构建了一个DLL，我试图用它来包装Java代码，但是我在运行Java程序时遇到了一些麻烦。我写了一个简单的测试DLL和Java程序，并产生相同的错误，虽然有很多关于NoClassDefFoundError在线的资源我似乎无法解决我的任何故障排除方法。

这是我的D:\Test1.Java文件

public class Test1 { 

    static {
        //System.loadLibrary("HeyLand");
        System.load("D://HeyLand.dll");
    }

    public native void displayHeyLand();

    public static void main (String[] args) {
        Test1 t = new Test1();
        t.displayHeyLand();
    }
}

编译后，尝试运行D:\Test1.class会产生以下结果：

D:\>java Test1.class
Exception in thread "main" java.lang.NoClassDefFoundError: Test1.class
Caused by: java.lang.ClassNotFoundException: Test1.class
        at java.net.URLClassLoader.findClass(URLClassLoader.java:434)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:660)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:358)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:626)
Could not find the main class: Test1.class.  Program will exit.

为什么我难倒？
1.我已将类路径设置为D:\，所以我相信我的类定义将在类路径中，并且我看不出我的编译时和运行时类路径是如何有所不同的。
2.我不知道这与静态初始化有什么关系，我相信异常看起来会有所不同。

也许我只是错过了一些非常简单的东西，我是Java的新手。

非常感谢任何帮助！

Answer 1

classpath环境变量优先于java run命令中的变量。您需要指定类位置（以及删除.class文件扩展名）

java -cp . Test1

Answer 2

Java normal syntax for executing class file is 
Java [<options>....} <class-name> [<arguments>....]


For example 

java com.package.name.Test1

here how compiler works

1. Compiler search for complete class name
2. Load that class
3. check for main method - in the same class
4. Call main method with passed arguments in command line string.



Now following are the possibilities why your class may not found main method.
1 - forgot to include package name
    I am new developer in java but I found when I run application using eclips or intellJ editor it gives different path and package name and execute code as I noticed it on command line edior. So make sure you are including package name 

    For example:
    java com.package.name.Test1 instead of 
    java Test1 

2. File name or pathname rather then class name
   As I noticed output file is in different location. That why class file path was different.
   java Test1.class
   java com/package/name/Test1.class

3. Typo


also I noticed you are using 
  static {
        //System.loadLibrary("HeyLand");
        System.load("D://HeyLand.dll");
    }


 Is this function ? or constructor? If it is function then where is name of the function? You cant write code without any reference in classs

不确定NoClassDefFoundError背后的原因

2 个答案: