Java软件包无法编译

Question

I think my understanding of how to set up a Java package might be missing something because I cannot get my package to compile. I have 3 class files. My directory looks like this: ...Documents\\jsjf which contains: ArrayStack.java and StackADT.java. Within the jsjf directory I also have a folder "EmptyCollectionException" which contains EmptyCollectionException.java. I can compile EmptyCollectionException.java and StackADT.java but when I try to compile ArrayStack.java I get the following error messages (see link): http://i.stack.imgur.com/koJ8P.jpg

Here is the top part of each part of my code for each file. Does anyone know what the problem is here. Why is ArrayStack not able to import the package?

For ArrayStack.java

package jsjf;



import jsjf.EmptyCollectionException;
import java.util.Arrays;

public class ArrayStack<T> implements StackADT<T>
{
   private final int DEFAULT_CAPACITY = 100;
   private int top;
   private T[] stack;



   //-----------------------------------------------------------------
   //  Creates an empty stack using the specified capacity.
   // Note top is now initialized at -1 so that when first
   // element is added an top is decremented, top will equal 0
   // corresponding to the array index of the first element.
   //-----------------------------------------------------------------
   public ArrayStack(int initialCapacity)
   {
      top = -1;
      stack = (T[]) (new Object[initialCapacity]);
   }

   //-----------------------------------------------------------------
   //  Creates an empty stack using the default capacity.
   //-----------------------------------------------------------------
   public ArrayStack()
   {
      this(DEFAULT_CAPACITY);
   }


//Rest of code.......

For EmptyCollectionException.java:

package jsjf.exceptions;


public class EmptyCollectionException extends RuntimeException
{
    /**
     * Sets up this exception with an appropriate message.
     * @param collection the name of the collection
     */
    public EmptyCollectionException(String collection)
    {
        super("The " + collection + " is empty.");
    }
}

For StackADT:

package jsjf;


public interface StackADT<T>
{
    /**  
     * Adds the specified element to the top of this stack. 
     * @param element element to be pushed onto the stack
     */

    //Rest of Code

Answer 1

Firstly, a package name should not start with an upper case. It would have helped you to see that jsjf.EmptyCollectionException does not point to a class in your hierarchy but to a package. Therefore, after renaming the package according to the Java naming conventions, the correct import should be :

import jsjf.emptyCollecionException.EmptyCollectionException

In you exception class, you use another package name ( exceptions ). The package name should match the name of the parent directory. Therefore, I woul rename the directory containing EmptyCollectionException to exception and fix the import in ArrayStack .

Finally, I strongly recommend you to work with an IDE when you will have compiled some classes manually just to know how it works. An IDE will help you with the imports, compilation, and lots of other things

Answer 2

Your code is saying you expect EmptyCollectionException to be in the package jsjf , but you say that class exists in a subfolder, which would be deeper in the package hierarchy (and counter to Java naming conventions, where package names usually aren't camel-cased).

Your EmptyCollectionException class code says it's in the jsjf.exceptions package, meaning (a) it should be in the exceptions folder under the jsjf folder, and your import of EmptyCollectionException should be import jsjf.exceptions. EmptyCollectionException import jsjf.exceptions. EmptyCollectionException .

You also need to be in a reasonable place when you compile, eg, your documents folder since packages would live "underneath" where you're compiling from. Personally, I'd put this into a more reasonable folder location, preferably without spaces, somewhere not under a Windows documents folder.