今日课程：

class Supermarket {
    private int price; // Instance variables, using private for better encapsulation
    private int discount;
    private String productName;

    // Parameterized constructors
    public Supermarket(String productName, int price, int discount) {
        this.price = price;
        this.discount = discount;
        this.productName = productName;
    }

    public Supermarket(String productName, int price) {
        this.price = price;
        this.productName = productName;
        this.discount = 0; // Default discount if not provided
    }

    public static void main(String[] args) {
        Supermarket product1 = new Supermarket("Good Day", 10, 2);
        Supermarket product2 = new Supermarket("Rice", 55);

        System.out.println(product1.getProductName()); // Accessing using getter method
        System.out.println(product2.getProductName());

        product1.buy();
        product1.returnProduct();
    }

    // Methods for better readability and maintainability
    public void buy() {
        System.out.println("Buying " + productName + " for " + (price - discount));
    }

    public void returnProduct() {
        System.out.println("Returning " + productName + " for " + price);
    }

    // Getter method for productName
    public String getProductName() {
        return productName;
    }
}

The improved code uses private instance variables (price, discount, productName) for better encapsulation, preventing direct access and modification from outside the class. It also introduces getter methods (like getProductName()) for controlled access to the instance variables. The names of the methods have been made more descriptive (e.g., return_product changed to returnProduct). Finally, a default discount of 0 is set in the constructor that takes only the product name and price. This makes the code more robust and easier to understand and maintain.

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