Java in a Nutshell, 5th Edition

Name

Properties

Synopsis

This class is an extension of Hashtable that allows key/value pairs to be read from and written to a stream. The Properties class implements the system properties list, which supports user customization by allowing programs to look up the values of named resources. Because the load( ) and store( ) methods provide an easy way to read and write properties from and to a text stream, this class provides a convenient way to implement an application configuration file.

When you create a Properties object, you may specify another Properties object that contains default values. Keys (property names) and values are associated in a Properties object with the Hashtable method put( ). Values are looked up with getProperty( ); if this method does not find the key in the current Properties object, it looks in the default Properties object that was passed to the constructor method. A default value can also be specified, in case the key is not found at all. Use setProperty( ) to add a property name/value pair to the Properties object. This Java 1.2 method is preferred over the inherited put( ) method because it enforces the constraint that property names and values be strings.

propertyNames( ) returns an enumeration of all property names (keys) stored in the Properties object and (recursively) all property names stored in the default Properties object associated with it. list( ) prints the properties stored in a Properties object, which can be useful for debugging. ...