diff --git a/1ano/2semestre/poo/src/aula04/CashRegisterDemo.java b/1ano/2semestre/poo/src/aula04/CashRegisterDemo.java
new file mode 100644
index 0000000..36f6c44
--- /dev/null
+++ b/1ano/2semestre/poo/src/aula04/CashRegisterDemo.java
@@ -0,0 +1,85 @@
+package aula04;
+
+class Product {
+    private final String name;
+    private final double price;
+    private final int quantity;
+
+    public Product(String name, double price, int quantity) {
+        this.name = name;
+        this.price = price;
+        this.quantity = quantity;
+    }
+
+    public double getTotalValue() {
+        return price * quantity;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public double getPrice() {
+        return price;
+    }
+
+    public int  getQuantity() {
+        return quantity;
+    }
+}
+
+
+class CashRegister {
+
+    // TODO: completar implementação da classe
+    private final Product[] products = new Product[5];
+
+    public void addProduct(Product p) {
+        for (int i = 0; i < products.length; i++) {
+            if (products[i] == null) {
+                products[i] = p;
+                break;
+            }
+        }
+    }
+
+    public double getTotalValue() {
+        double total = 0;
+        for (Product product : products) {
+            if (product != null) {
+                total += product.getTotalValue();
+            }
+        }
+        return total;
+    }
+
+    public String toString() {
+        String result = String.format("%-15s %10s %10s %7s\n", "Product", "Price", "Quantity", "Total");
+        for (Product product : products) {
+            if (product != null) {
+                result += String.format("%-15s %10.2f %10d %7.2f\n", product.getName(), product.getPrice(), product.getQuantity(), product.getTotalValue());
+            }
+        }
+        result += String.format("%s %.2f\n", "Total value: ", getTotalValue());
+        return result;
+    }
+
+}
+
+public class CashRegisterDemo {
+
+    public static void main(String[] args) {
+
+        // Cria e adiciona 5 produtos
+        CashRegister cr = new CashRegister();
+        cr.addProduct(new Product("Book", 9.99, 3));
+        cr.addProduct(new Product("Pen", 1.99, 10));
+        cr.addProduct(new Product("Headphones", 29.99, 2));
+        cr.addProduct(new Product("Notebook", 19.99, 5));
+        cr.addProduct(new Product("Phone case", 5.99, 1));
+        
+        // TODO: Listar o conteúdo e valor total
+        System.out.println(cr);
+
+    }
+}
\ No newline at end of file
diff --git a/1ano/2semestre/poo/src/aula04/Shapes.java b/1ano/2semestre/poo/src/aula04/Shapes.java
new file mode 100644
index 0000000..af75682
--- /dev/null
+++ b/1ano/2semestre/poo/src/aula04/Shapes.java
@@ -0,0 +1,118 @@
+package aula04;
+
+class Circle {
+    public double radius;
+    
+    public Circle(double radius) {
+        if (radius <= 0)
+            return;
+        this.radius = radius;
+    }
+
+    public double getRadius() {
+        return this.radius;
+    }
+
+    public void setRadius(double radius) {
+        this.radius = radius;
+    }
+
+    public boolean equals(Circle c2) {
+        return this.radius == c2.radius;
+    }
+
+    public String toString() {
+        return "Circle with radius " + this.radius;
+    }
+
+    public double getArea() {
+        return Math.PI * Math.pow(this.radius, 2);
+    }
+
+    public double getPerimeter() {
+        return 2 * Math.PI * this.radius;
+    }
+}
+
+class Triangle {
+    public double side1;
+    public double side2;
+    public double side3;
+
+    public Triangle(double side1, double side2, double side3) {
+        if (side1 <= 0 || side2 <= 0 || side3 <= 0)
+            return;
+        this.side1 = side1;
+        this.side2 = side2;
+        this.side3 = side3;
+    }
+
+    public double[] getSides() {
+        return new double[] {this.side1, this.side2, this.side3};
+    }
+
+    public void setSides(double side1, double side2, double side3) {
+        this.side1 = side1;
+        this.side2 = side2;
+        this.side3 = side3;
+    }
+
+    public boolean equals(Triangle c2) {
+        return this.side1 == c2.side1 && this.side2 == c2.side2 && this.side3 == c2.side3;
+    }
+
+    public String toString() {
+        return "Triangle with sides " + this.side1 + ", " + this.side2 + ", " + this.side3;
+    }
+
+    public double getArea() {
+        double p = this.getPerimeter() / 2;
+        return Math.sqrt(p * (p - this.side1) * (p - this.side2) * (p - this.side3));
+    }
+
+    public double getPerimeter() {
+        return this.side1 + this.side2 + this.side3;
+    }
+}
+
+class Rectangle {
+    public double side1;
+    public double side2;
+
+    public Rectangle(double side1, double side2) {
+        if (side1 <= 0 || side2 <= 0)
+            return;
+        this.side1 = side1;
+        this.side2 = side2;
+    }
+
+    public double[] getSides() {
+        return new double[] {this.side1, this.side2};
+    }
+
+    public void setSides(double side1, double side2) {
+        this.side1 = side1;
+        this.side2 = side2;
+    }
+
+    public boolean equals(Rectangle c2) {
+        return this.side1 == c2.side1 && this.side2 == c2.side2;
+    }
+
+    public String toString() {
+        return "Rectangle with sides " + this.side1 + ", " + this.side2;
+    }
+
+    public double getArea() {
+        return this.side1 * this.side2;
+    }
+
+    public double getPerimeter() {
+        return 2 * (this.side1 + this.side2);
+    }
+}
+
+public class Shapes {
+    public static void main(String[] args) {
+    }
+}