Java For Dummies Quick Reference

java Command

The java command runs a Java program from a command prompt. The basic syntax is

java filename [options]

When you run the java command, the JRE is loaded along with the class you specify. Then, the main method of that class is executed.

Here’s an example that runs a program named HelloApp:

C:\java\samples>java HelloApp

The bold indicates the part you type.

The class must be contained in a file with the same name as the class, and its filename must have the extension .class. You typically don’t have to worry about the name of the class file because it’s created automatically when you compile the program with the javac command.

The Java runtime command lets you specify options that can influence its behavior.

Option	Description
-? or -help	Lists standard options
-classpath directories and archives	Lists the directories or JAR or Zip archive files used to search for class files
-client	Runs the client virtual machine
-cp <search path>	Does the same thing as -classpath
-D name=value	Sets a system property
-dsa or -disablesystemassertions	Disables system assertions
-ea classes or packages	Enables assertions for the specified classes or packages
-ea or -enableassertions	Enables the assert command
-esa or ...