JDK Tutorials - Herong's Tutorial Examples - v6.32, by Herong Yang
Importing Classes from Unnamed to Named Packages
This section provides a tutorial example on how to import classes defined in an unnamed package to a named package. The imported class must be defined as 'public'.
Recently, I received an email from a reader asking me how to refer to a class defined in an unnamed package if the calling class is in a named class with JDK 1.4.1 or higher. To answer this question, let's enter a new class called "ImportingHelloCom" in a package called "com", and run the following commands:
\herong\tmp> more com\ImportingHelloCom.java /* ImportingHelloCom.java * Copyright (c) HerongYang.com. All Rights Reserved. */ package com; import Hello; public class ImportingHelloCom { public static void main(String[] a) { System.out.println("Calling the imported Hello.main()..."); Hello.main(a); } } \herong\tmp> more Hello.java class Hello { public static void main(String[] a) { System.out.println("Hello world!"); } } \herong\tmp> del *.class Could Not Find \herong\tmp\*.class \herong\tmp> del com\*.class Could Not Find \herong\tmp\com\*.class \herong\tmp> \jdk1.3.1_05\bin\javac com\ImportingHelloCom.java com\ImportingHelloCom.java:5: cannot resolve symbol symbol: class Hello import Hello; ^ com\ImportingHelloCom.java:9: cannot resolve symbol symbol : variable Hello location: class ImportingHelloCom Hello.main(a); ^ 2 errors \herong\tmp> \jdk1.3.1_05\bin\javac -classpath . com\ImportingHelloCom.java com\ImportingHelloCom.java:6: Hello is not public in empty package; cannot be accessed from outside package import Hello; ^ com\ImportingHelloCom.java:10: Hello is not public in empty package; cannot be accessed from outside package Hello.main(a); ^ com\ImportingHelloCom.java:10: main(java.lang.String[]) in Hello is not defined in a public class or interface; cannot be accessed from outside package Hello.main(a); ^ 3 errors
This test shows us that:
To fix the last compilation error, just declare the Hello class as "public". Now let's modify the classes and run the following commands:
\herong\tmp> more Hello.java public class Hello { public static void main(String[] a) { System.out.println("Hello world!"); } } \herong\tmp> del *.class Could Not Find \herong\tmp\*.class \herong\tmp> del com\*.class Could Not Find \herong\tmp\com\*.class \herong\tmp> \jdk1.3.1_05\bin\javac -classpath . com\ImportingHelloCom.java \herong\tmp> \jdk1.3.1_05\bin\java -classpath . com.ImportingHelloCom Calling the imported Hello.main()... Hello world!
As you can see, importing a class defined in an unnamed package into a class defined in a named package is easy with JDK 1.3.1.
Table of Contents
Date, Time and Calendar Classes
Date and Time Object and String Conversion
Number Object and Numeric String Conversion
Locales, Localization Methods and Resource Bundles
►Calling and Importing Classes Defined in Unnamed Packages
One Class in an Unnamed Package - Hello.java
Two Classes in Unnamed Packages - Hello.java and CallingHello.java
Importing Classes Defined in Unnamed Packages
►Importing Classes from Unnamed to Named Packages
Importing Classes from Unnamed to Named Packages - JDK 1.4.1
HashSet, Vector, HashMap and Collection Classes
Character Set Encoding Classes and Methods
Encoding Conversion Programs for Encoded Text Files
Datagram Network Communication
DOM (Document Object Model) - API for XML Files
DTD (Document Type Definition) - XML Validation
XSD (XML Schema Definition) - XML Validation
XSL (Extensible Stylesheet Language)
Message Digest Algorithm Implementations in JDK
Private key and Public Key Pair Generation
PKCS#8/X.509 Private/Public Encoding Standards
Digital Signature Algorithm and Sample Program
"keytool" Commands and "keystore" Files
KeyStore and Certificate Classes
Secret Key Generation and Management
Cipher - Encryption and Decryption
The SSL (Secure Socket Layer) Protocol
SSL Socket Communication Testing Programs