\documentclass {jarticle}
\begin{document}
Hello TeX world.
\end{document}

\documentclass {jarticle}
\begin{document}
Hello TeX world.

$$ f(x) = a_{0} + \sum_{n=1}^\infty \left
   a_{n} cos {n\pi x \over L}
   + b_{n} sin {n \pi x \over L } \right) $$

\end{document}

#include <stdio.h>
main()
{
   printf(“How are you?\n”);
}

public class hello {
	public static void main { String arg[] ) {
		System.out.println ( "Hello Java World." );
	}
}

public class hello{
        public static void main ( String args[] ) {
                int     i;
                int     t;
                t = 0;
                for ( i = 1; i <= 1000; i++ ) {
                        t = t + i;
                }
                System.out.println ( "t = " + t );
        }
}

      program test2
        print *,"Hello fortran"
      end program