Calculating Area With JOptionPane?

I am supposed to be doing a class assignment that calculates the area of a triangle and outputs with JOptionPane. I was able to fix some errors, but it's uncovering more errors.Here is my code:

import javax.swing.JOptionPane;
import java.util.*;
import java.text.DecimalFormat;
import java.util.StringTokenizer;

public class Area {
public static void main (String [] args) {
double a, b, c; //Input sides of triangle
double x; //Perimeter of triangle
double area; //Area of triangle
StringTokenizer st;

[code]....