objects , writing files

this may be a long shot , but im totally stuck and need help. i have a farely large project where we have to read in some some numbers, and these numbers represent triangles and will be used to make a picture of a tea pot. ive got about 65% of the project done , except i dont understand how to write to a file. there are 2 methods in my model class , which are writeDatatoFile and writeInfotoFile. write data to file just writes back whatever ive read in and should have a line containing the keyword triangle followed by three lines, each with information for each vertex. i think once i figure out how to do this part , i can figure out the writeInfoToFile method , which writes all the into out ( like the max,min). i know how t write out to a file , but im having problems seeing how to implement it. i just cant see the big picture. ill paste the code below , its split into 6 classes. App, D3V, Model,Triangle, vector and vertex.


this is my model class , this is were the 2 write to file methods are.

 

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Scanner;

public class Model {

	ArrayList<Triangle> triangles = new ArrayList<Triangle>();

	void readFromFile(String filename) {
		File file = new File(filename);
		readFromFile(file);
	}

	void writeDataToFile(File file) {
		
	}

	void writeInfoToFile(File file) {
		// please implement this method...
		// double a = m.computeSurfaceArea();
		// System.out.println("total surface area = " + a);
	}

	void readFromFile(File file) {
		try {
			Scanner s2 = new Scanner(file);
			while (s2.hasNext()) {
				s2.nextLine();
				String[] threeLines = { 
						s2.nextLine(), 
						s2.nextLine(),
						s2.nextLine() 
				};
				triangles.add(new Triangle(threeLines));
			}
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		}
	}
	
	double computeSurfaceArea() {
		double v = 0;
		// loop through each triangle and sum up their areas
		for ( Triangle t : triangles )
		{
			double sArea = t.computeArea();
			v += sArea;
		}
		return v;
	}
	double averageSurface(){
		double v = 0;
		int count = 0;
		for ( Triangle t : triangles){
			
			double aAverage =t.computeArea();
			count++;
			v += aAverage;
			
			
		       	
		}
		return v/count;
		}
	 double computeMax(){
		 double maxValue= 0;
		 for ( Triangle t : triangles) {
			 
			 double areaT = t.computeArea();
			if (areaT> maxValue ){
				maxValue =areaT;
				
			} 
			 
		 }
		return maxValue;
				
		}  
	
	 double computeMin(){  
		 double minValue= 0;
		 for ( Triangle t : triangles) {
			 
			 double areaT = t.computeArea();
			if (areaT < minValue ){
				minValue =areaT;
				
			} 
			 
		 }
		return minValue;
				
		}  
		
		
		
	}

triangle class

public class Triangle {

	Triangle(String[] lines) {
		this.points = new Vertex[3];
		for (int i = 0; i < 3; i++)
			this.points[i] = new Vertex(lines[i]);
	}

	Vertex points[]; // array of vertices 
	
	public String toString() {
		String buffer = "";
		for (Vertex point : points) {
			buffer += point.toString() + "\n";
		}
		return buffer;
	}
	
	  double computeArea() {
		
		double area = 0.0;
		
		D3V uu = D3V.sub(points[0].position, points[2].position);
		D3V vv = D3V.sub(points[1].position, points[2].position);
		
		area = 0.5 * Vector.length(Vector.cross(uu,vv));
		
		return area;
	}
	
}

vector class

public class Vector extends D3V {
	
	public Vector(double d, double e, double f) {
		super(d, e, f);
	}

	static double length(Vector u) {
		return Math.sqrt(u.x*u.x + u.y*u.y + u.z*u.z);
	}

	public static Vector cross(D3V u, D3V v) {
		return new Vector(
			u.y * v.z - u.z * v.y,
			u.z * v.x - u.x * v.z,
			u.x * v.y - u.y * v.x
		);
	}

	public static Vector dot(D3V u, D3V v) {
		return new Vector(u.x*v.x,u.y*v.y,u.z*v.z);
	}
}

vertex class

public class Vertex {
	
	D3V position;
	D3V normal;
	double u;
	double v;
	
	Vertex() {
		position = new D3V();
		normal = new D3V();
	}
	
	public String toString() {
		String buffer = "";
		// fill in buffer with P(x,y,z), N(x,y,z), u, and v
		return buffer;
	}
	
	double X() { 
		return position.x;
	}
	
	double Nx() {
		return normal.x;
	}
	
	Vertex(String line) {
		String[] array = line.split("\\s+");
		int idx = 0;
		position.x = Double.parseDouble(array[idx++]);
		position.y = Double.parseDouble(array[idx++]);
		position.z = Double.parseDouble(array[idx++]);
		normal.x=Double.parseDouble(array[idx++]);
		normal.y=Double.parseDouble(array[idx++]);
		normal.z=Double.parseDouble(array[idx++]);
		// etc..
	}

	public Vertex(double x, double y, double z) {
		position = new D3V(x,y,z);
	}
	
	public Vertex(double px, double py, double pz, double nx, double ny, double nz) {
		position = new D3V(px,py,pz);
		normal = new D3V(nx,ny,nz);
	}
}

D3V class

public class D3V {
	double x, y, z;

	public D3V() {
		x = 0; y = 0; z = 0;
	}
	
	public String toString() {
		// convert x, y, z to string
		return "";
	}
	
	public D3V(double d, double e, double f) {
		x = d; y = e; z = f;
	}

	public static D3V add(D3V a, D3V B)/>/> {
		return new D3V (a.x + b.x, a.y + b.y, a.z + b.z);
	}
	
	public static D3V sub(D3V a, D3V B)/>/> {
		return new D3V(a.x - b.x, a.y - b.y, a.z - b.z);
	}
}

app class , which runs it all

import java.io.File;

public class App {

	String changeExtension(String filename, String originalExtension, String newExtension) {
		int lastDot = filename.lastIndexOf(".");
		if (lastDot != -1) {
			return originalExtension.replace(originalExtension, newExtension);
		} 
		else 
		{
			return originalExtension + newExtension;
		}
	}



	public void Run(String inputFilename) {
		Model m = new Model();
		m.readFromFile(inputFilename);
		// write model's data
		String dataOutFilename = changeExtension(inputFilename, "asc", "out.txt");
		m.writeDataToFile(new File(dataOutFilename));

		// write model's info
		String infoOutFilename = changeExtension(inputFilename, "asc", "info.txt");
		m.writeInfoToFile(new File(infoOutFilename));
	}

	public static void main(String[] args) {
		App app = new App();
		app.Run(args[0]);
	}

}