This section provides a tutorial example on how to import classes defined in an unnamed package - done in the same as importing classed defined in named packages with JDK 1.3.1. But it is not allowed with JDK 1.4.1.
For classes defined in unnamed packages, their simple names are identical to their fully
qualified names. Therefore, there is no need to use import statement in the compilation
units where they are referred.
But if you really want to use an import statement, it shouldn't be a problem.
So let's enter another class, ImportingHello.java, in C:\hy\tmp directory,
and run the following commands to see what happens with the import statement:
C:\hy\tmp>type ImportingHello.java
/**
* ImportingHello.java
* Copyright (c) 2003 by Dr. Herong Yang
*/
import Hello;
public class ImportingHello {
public static void main(String[] a) {
System.out.println("Calling the imported Hello.main()...");
Hello.main(a);
}
}
C:\hy\tmp>del *.class
Could Not Find C:\hy\tmp\*.class
C:\hy\tmp>del ..\src\*.class
Could Not Find C:\hy\src\*.class
C:\hy\tmp>\jdk1.3.1\bin\javac -classpath ..\src ImportingHello.java
C:\hy\tmp>\jdk1.3.1\bin\java -classpath .;..\src ImportingHello
Calling the imported Hello.main()...
Hello world!
C:\hy\tmp>del *.class
C:\hy\tmp>del ..\src\*.class
As you can see, there is no problem. The import statement makes no impact on the compilation
and execution processes with JDK 1.3.1.
However, the import statement will cause compilation problem if we use JDK 1.4.1,
see the following commands and outputs:
Obviously, specification on import statement has been changed. With JDK 1.4.1, import
statement can not be used on compilation units in unnamed packages. So, from now on,
stop use import statements on classes or interfaces defined in unnamed packages.
