an error about import p1.*

[Mike Lin]

Hi ,all,I meet a confused compile question today.
create two java source file named T1.java and T2.java in the same directory,then comiple them.
T1.java

package p1;
public class T1{}

T2.java

import p1.T1;
public class T2{  
 T1 t=new T1();
}

compile T1 first ,then compile T2.Nothing exceptions happen.
But change

import p1.T1; 

to

import p1.*;

in T2.java,a compile error happens.compile messages like these:

D:\temp>javac T2.javaT2.java:3: cannot access T1
bad class file: .\T1.javafile does not contain class T1
Please remove or make sure it appears in the correct subdirectory of the classpath.
T1 t=new T1();   ^1 error

Yet ,what's the difference between import p1.* and import p1.T1


EDIT by mw: Broke up really long error message line in code tags.
[ October 10, 2006: Message edited by: marc weber ]

[wise owen]

Both cases had compile error on my machine.

[marc weber]

This is a little sticky, but I'll try it.

"A single-type-import declaration imports a single type by giving its canonical name, making it available under a simple name..." (JLS - 7.5.1) So with import p1.T1; the canonical name is easily resolved, and makes T1 available under its simple name.

But a "type-import-on-demand [i.e. "wildcard"] declaration allows all accessible (�6.6) types declared in the type or package named by a canonical name to be imported as needed." (JLS - 7.5.2) So with import p1.*; the compiler needs to go looking for what you mean by the simple name T1. It starts in the current directory (denoted by "."). And indeed, there is a T1.class in the current directory (p1).

But now the compiler says...
bad class file: ./T1.class
class file contains wrong class: p1.T1

The compiler is finding T1 in the current directory (./T1). But this considered a "bad class file" because T1 is really in a package called p1, and what the compiler thinks it's found (./T1) isn't matching what that file actually contains (p1.T1).

So the compiler makes a suggestion...
Please remove or make sure it appears in the correct subdirectory of the classpath.


Question: Have you started working with "classpath" yet?
[ October 10, 2006: Message edited by: marc weber ]

[marc weber]

Please continue under the cross-post in the beginners forum, and please don't cross-post.