'java' - The Java Launcher
Part:
1
2
3
4
This chapter describes:
- "java" Command
- Hello.java - My First Application
- "-classpath" - Specifying Class Path
- "-jar" - Executable JAR Files
- "-X" Options to Control Memory Size
- "javaw" - Launching Java Applications without Console
"java" Command
"java": A command line tool that launches Java applications. It starts a Java virtual machine,
loads the specified class, and invokes that class's main method. "java" has the following syntax:
java [options] class [arguments]
where "options" is a list of options; "class" is the full name of a Java class to be launched;
"arguments" is a list of arguments to be passed to the main method of the class to be launched.
Another way of launching a Java class is to use the "-jar" option:
java [options] -jar file [arguments]
where "file" is a JAR file, which should contain a "Main-Class" attribute in the manifest file.
The "Main-Class" attibute defines the Java class to be launched.
Commonly used options are:
- "-help" - Displays a short help text.
- "-verbose" - Generates verbose output to standard output.
- "-version" - Prints the version information of the launcher.
- "-classpath classpath" - Specifies a list of path names where the launcher will search for compiled type definitions.
If "-classpath" is not specified, the current directory will be used as the class path.
- "-Dproperty=value" - Defines a new system property, which can be accessed by the application.
Hello.java - My First Application
To test the Java launcher, I wrote the following Java file, Hello.java:
class Hello {
public static void main(String[] a) {
System.out.println("Hello world!");
}
}
Here is what I did in a command window to compile Hello.java into Hello.class:
>javac Hello.java
>dir Hello.*
416 Hello.class
116 Hello.java
>java Hello
Hello world!
As you can see, launching a Java application is easy.
(Continued on next part...)
Part:
1
2
3
4
|