class HelloWorld {
     public static void main(String[] args) {
       System.out.println("Hello World!");            
     }
}

> gcj HelloWorld.java
/usr/lib64/gcc/x86_64-*****-linux/4.1.2/../../../../lib64/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
collect2: ld returned 1 exit status