Using System Properties
One obscure feature of the JDK is that the command-line option -D can modify the performance of the Java class library.
If you have used other programming languages prior to learning Java, you might be familiar with environment variables, which provide information about the operating system in which a program is running. An example is the CLASSPATH setting, which indicates the folders in which the Java interpreter should look for a class file.
Because different operating systems have different names for their environment variables, they cannot be read directly by a Java program. Instead, Java includes a number of different system properties that are available on any platform with a Java implementation.
Some properties ...
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