Accessing

// get a system property
String vendor = System.getProperty( "java.vendor" );
System.out.println( vendor );

Unfortunately that code produces a list in scrambled order. It won’t be either alphabetical or in the order of the original properties file, because underneath, Properties are just Hashtables.

The System properties are generated by a magic native method System.initProperties. There is no corresponding jar element or *.properties file on disk. file. You can temporarily add a System property with the -D option on the java.exe line. You can also use the technique to pass the value of a SET variable in as a system property. For Applets, there is a similar PARAM mechanism that generates a properties table.

Overriding Properties on the Command Line

Security And System Properties

System.getProperty( "java.version" );

System.getProperties().getProperty( "java.version" );

Here is how you set a system property:

// turn on anti-aliasing for smooth fonts.
System.setProperty( "swing.aatext", "true" );

The only way I know of to determine which properties are safe in unsigned Applets and which are restricted to applications and signed Applets is to write test Applet to fetch the properties and see which ones raise an Exception. I used an unsigned version of Wassup to create this table.

There are also system properties for proxies that you are not present when there are no proxies.

There are no system properties to tell you about the JDK.

There is no system property to tell you how many cpus there are. However, you can get it with Runtime.availableProcessors.

os.name

User Properties

Since Properties are Hashtables, they scramble the order of the elements. If you want to preserve order, and don’t need key lookup, you can parse the file yourself with a StreamTokenizer and put it in an array. See how com.mindprod.business.Misc.loadProprerties code used by Learn To Count loads its ordered list of languages and classes from a properties file. Learn to Count keeps its properties file in the jar file. It accesses the file with:

To create a new Properties file from scratch programmatically, remember that java.util.Properties is a subclass of java.util.Hashtable. Just create a new Properties object, add the elements to it as if it were a Hashtable and finally save it with Properties.store() or the JDK 1.2-deprecated Properties.save() in old Javas.

JavaBean Properties

Delphi Properties

Network Properties

Learning More