How to make Calculation In Java

import java.io.StringWriter;
import java.io.Writer;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.Velocity;

public class ProductList {

public static void main(String[] args) throws Exception {
Velocity.init();
Template t = Velocity.getTemplate("./src/calculation.vm");

VelocityContext ctx = new VelocityContext();

Collection products = new ArrayList();
products.add(new Product("Product 1", 12.99));
products.add(new Product("Product 2", 13.99));
products.add(new Product("Product 3", 11.99));
ctx.put("productList", products);

// calculate total
Iterator itr = products.iterator();
double total = 0.00;

while (itr.hasNext()) {
Product p = (Product) itr.next();
total += p.getPrice();
}

ctx.put("totalPrice", new Double(total));

Writer writer = new StringWriter();
t.merge(ctx, writer);

System.out.println(writer);
}
}

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public class Product {

private String name;
private double price;

public Product(String aName, double aPrice) {
name = aName;
price = aPrice;
}

public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
}