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考虑以下 java 程序：

import computer_package.Computer;
import com.sun.jna.Library;
public class HelloWorld {
    public static void main(String[] args) {
        Computer computer = new Computer();
        System.out.println("Hello, World");
    }
}

和以下目录结构：

Rebs-MacBook-Pro:jalint2 rebcabin$ find computer_package/
computer_package/
computer_package//Computer.class
computer_package//Computer.java

其中Computer.java如下：

package computer_package;
public class Computer {
    public Computer() {
        System.out.println("Constructor of Computer class.");
    }
    public void computer_method() {
        System.out.println("Power gone! Shut down your PC soon...");
    }
}

和另一个只有jar文件的目录：

Rebs-MacBook-Pro:jalint2 rebcabin$ find com
com
com/sun
com/sun/jna
com/sun/jna/jna-4.0.0.jar
com/sun/jna/jna-platform-4.0.0.jar

如果我只注释掉import com.sun.jna;原始HelloWorld.java文件中的行，那么一切正常

Rebs-MacBook-Pro:jalint2 rebcabin$ javac -g HelloWorld.java 
Rebs-MacBook-Pro:jalint2 rebcabin$ java HelloWorld
Constructor of Computer class.
Hello, World

Javac 和 java 能够在./computer_package/Computer.class没有任何进一步提示或注释或类路径黑客攻击的情况下找到类文件。

现在，如果我恢复该import com.sun.jna;行并仅注释掉import computer_package.Computer;构造 a 的行和行new Computer，并像这样编译：

Rebs-MacBook-Pro:jalint2 rebcabin$ javac -g -cp "./com/sun/jna/jna-4.0.0.jar" HelloWorld.java

甚至像这样：

Rebs-MacBook-Pro:jalint2 rebcabin$ make
javac -g -cp "./com/sun/jna/jna-4.0.0.jar:./computer_package" HelloWorld.java

那么一切都很好：

Rebs-MacBook-Pro:jalint2 rebcabin$ java HelloWorld
Hello, World

At least, the import com.sun.jna; line didn't throw a compiler error -- admittedly, I am not yet using the jna library; I'm just trying to build up to that momentous achievement in baby steps.

So if I now cautiously uncomment the import computer_package; line and the line that constructs an instance of Computer, yielding the HelloWorld.java file at the top of this question that tries to use both my Computer class and jna, all hell breaks loose; the previously acceptable Computer class is now inaccessible:

Rebs-MacBook-Pro:jalint2 rebcabin$ make
javac -g -cp "./com/sun/jna/jna-4.0.0.jar:./computer_package" HelloWorld.java
HelloWorld.java:20: error: package computer_package does not exist
import computer_package.Computer;
                       ^
HelloWorld.java:25: error: cannot access Computer
        Computer computer = new Computer();
        ^
  bad class file: ./computer_package/Computer.class
    class file contains wrong class: computer_package.Computer
    Please remove or make sure it appears in the correct subdirectory of the classpath.
2 errors
make: *** [HelloWorld.class] Error 1

I know this is elementary; I am not a java expert and I admit I am trying to guess my way around the classpath nightmare world; I am using just emacs and bash, avoiding the IDEs that add even more layers of opaque abstraction.

4

1 回答 1

2

You need to specify the classpath as the directory containing the package, not the package's classes, so if you're running from the same directory:

javac -g -cp "./com/sun/jna/jna-4.0.0.jar:./"

Note that, when you don't specify a classpath, the current directory is used by default. See http://docs.oracle.com/javase/tutorial/essential/environment/paths.html

于 2013-08-12T00:00:52.770 回答