Learning Java

Properties

The java.util.Properties class is a specialized hashtable for strings. Java uses the Properties object to replace the environment variables used in other programming environments. You can use a Properties object (or “table”) to hold arbitrary configuration information for an application in an easily accessible format. The Properties object can also load and store information using streams (see Chapter 10, for information on streams).

Any string values can be stored as key/value pairs in a Properties table. However, the convention is to use a dot-separated naming hierarchy to group property names into logical structures, as is done with X Window System resources on Unix systems.^[36] The java.lang.System class provides system-environment information in this way, through a system Properties table we’ll describe shortly.

Create an empty Properties table and add String key/value pairs just as with any Hashtable:

Properties props = new Properties( );  
props.put("myApp.xsize", "52");  
props.put("myApp.ysize", "79");

Thereafter, you can retrieve values with the getProperty( ) method:

String xsize = props.getProperty( "myApp.xsize" );

If the named property doesn’t exist, getProperty( ) returns null. You can get an Enumeration of the property names with the propertyNames( ) method:

for ( Enumeration e = props.propertyNames( ); e.hasMoreElements; ) {
    String name = e.nextElement( );  
    ...  
}

Default Values

When you create a Properties table, you can specify a second table for default property ...