JDK Tutorials - Herong's Tutorial Examples - v6.32, by Herong Yang
What Is an Unnamed Package?
This section describes what is an unnamed package - a package of compilation units with no package name. The main question is how to refer to a compilation unit in an unnamed package.
Unnamed packages contain compilation units (classes or interfaces) that have no package declaration statement. For example, the following class is a compilation unit in an unnamed package, Hello.java:
class Hello { public static void main(String[] a) { System.out.println("Hello world!"); } }
There are a number of questions about unnamed packages we need to answer:
Based on the documentation of JDK for Windows system, my guess is that JDK supports multiple unnamed packages. Each unnamed package is stored in the top directory of each class path specified in one of the following three ways:
Let's do some tests to answer these questions and to confirm my guess in next sections.
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