What are Java applications?

A Java application is a conventional program. It must have a ‘method’ (i.e., a function) called main.

Suppose the file HWTion.java contains the Java application:

0001: public class HWTion {                                         // HWTion.java
0002:    public static void main(String[ ] args) {
0003:       System.out.println("Hello World!");
0004:    }
0005: }

Note: the line numbers should be ignored: they do not form part of the program.

The application can be compiled by using the Unix/MS-DOS command:
```
javac HWTion.java
```
This produces a file of bytecodes in the file HWTion.class.
The file HWTion.class can be interpreted (i.e., executed) by using the command:
```
java HWTion
```
At the University of Durham, the commands javac and java currently run the compiler and interpreter of the Java 2 SDK v 1.4.1-01. All the commands of JDK 1.1.x can be accessed by following a command name with a minus sign, and those of JDK 1.0.2 can be accessed by using two minus signs. Here are some examples:
```
javac-- HWTion.java
java-- HWTion
```