Importing Classes Defined in Unnamed Packages

JDK Tutorials - Herong's Tutorial Examples

∟Calling and Importing Classes Defined in Unnamed Packages

∟Importing Classes Defined in Unnamed Packages

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 \herong\tmp directory, and run the following commands to see what happens with the import statement:

\herong\tmp> more ImportingHello.java
/* ImportingHello.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
import Hello;
public class ImportingHello {
   public static void main(String[] a) {
      System.out.println("Calling the imported Hello.main()...");
      Hello.main(a);
   }
}

When I tried to compile this program with JDK 1.4 or higher, I got a compilation error:

\herong\tmp> javac -classpath ..\src ImportingHello.java
ImportingHello.java:5: '.' expected
import Hello;
            ^
1 error

So importing a class from a unnamed package is not supported.

But this was supported back in JDK 1.3:

\herong\tmp> del *.class
Could Not Find \herong\tmp\*.class

\herong\tmp> del ..\src\*.class
Could Not Find \herong\src\*.class

\herong\tmp> \jdk1.3.1_05\bin\javac -classpath ..\src ImportingHello.java

\herong\tmp> \jdk1.3.1_05\bin\java -classpath .;..\src ImportingHello
Calling the imported Hello.main()...
Hello world!

\herong\tmp> del *.class

\herong\tmp> del ..\src\*.class