MultFiles

Working with Multiple Files

In Java, each public class is resides in its own file. As each program is usually composed of many classes, this means you will have many different files.

Compiling:

In order to compile the files A.java, B.java and C.java, you can use the command:

> javac A.java B.java C.java

Alternatively, in order to compile all the files with the extension .java in the current directory, you can use:

> javac *.java

Compiling like is done above will put the compiled .class files alongside the source .java files. It is sometimes convenient to separate the compiled files from the source files. You can use the -d switch to tell the compiler to put the class files in a specific folder.

> javac -d ../class *.java

will tell the compiler to create the .class files in the ../class directory.

Running

When you run a java program, you tell the java interpreter to run the void main(String[] args) method of a specific class.

For example, the commandline:

> java A

tells java to look at the A class (which is in the file A.class) and run its main(String[] args) method.

When doing its work, class A may want to create or send messages to other classes (for example B and C). This is not a problem, as long as java knows where the B.class and C.class files are. By default, java looks for the class files in the current directory. You can tell java (and javac) to look at other directories as well, using the -cp commandline switch.