2 · Interactive Console Input (Scanner Class)

In Java, reading keyboard inputs is managed by the Scanner utility class (located in package java.util). Using Scanner involves three steps: 在 Java 中，读取键盘输入由 java.util 包中的 Scanner 工具类进行管理。使用 Scanner 包含三个步骤：

1. Import:导入： Write reference statement at the top of the file: import java.util.Scanner;在文件顶部编写引用语句：import java.util.Scanner;
2. Declaration:声明： Create and bind Scanner object to input system: Scanner input = new Scanner(System.in);创建 Scanner 对象并绑定到输入流系统：Scanner input = new Scanner(System.in);
3. Reading:读取： Invoke input reading methods: int count = input.nextInt(); or double val = input.nextDouble();调用输入读取方法：int count = input.nextInt(); 或 double val = input.nextDouble();

3 · Formatting Program Output (printf)

The standard System.out.println() prints values raw, which often yields too many decimal places for monetary values. Instead, use System.out.printf() (formatted print) to control spacing and alignment: 标准的 System.out.println() 只是原始打印数据，这通常会导致金额值出现过多的小数位。相反，使用 System.out.printf()（格式化打印）来控制输出格式与宽度：

4 · Executable Program Logic Flow

When structuring interactive codes, the logic must run in sequential order: import utilities → declare class → declare Scanner → prompt user for input → read data → process formulas → format and output results → close scanner. 在结构化交互式代码中，逻辑必须按顺序执行：导入类库 → 声明类与主方法 → 声明 Scanner → 提示用户输入 → 读取数据 → 运行公式计算 → 格式化并输出结果 → 关闭 scanner。

Applied Case Study: Interactive Cafe Billing应用案例研究：交互式咖啡店账单

Company: Kompas Coffee House.
We write an interactive program that prompts the cashier for purchase details: quantity ordered, unit item price, and calculates total sales including a 6% service tax. 公司： Kompas Coffee House。
我们编写一个交互式程序，提示收银员输入商品购买明细：订购数量、商品单价，并计算包含 6% 服务税的总销售额。

import java.util.Scanner;

public class CoffeeRegister {{
    public static void main(String[] args) {{
        Scanner input = new Scanner(System.in);
        final double TAX_RATE = 0.06; // 6% service tax

        System.out.print("Enter item price (RM): ");
        double unitPrice = input.nextDouble();

        System.out.print("Enter quantity: ");
        int quantity = input.nextInt();

        double subtotal = unitPrice * quantity;
        double serviceTax = subtotal * TAX_RATE;
        double grandTotal = subtotal + serviceTax;

        System.out.println("\n--- KOMPAS COFFEE HOUSE RECEIPT ---");
        System.out.printf("Unit Price: RM %.2f%n", unitPrice);
        System.out.printf("Quantity:   %d units%n", quantity);
        System.out.printf("Subtotal:   RM %.2f%n", subtotal);
        System.out.printf("Tax (6%%):   RM %.2f%n", serviceTax);
        System.out.printf("Total Due:  RM %.2f%n", grandTotal);

        input.close();
    }}
}}

Enter item price (RM): 12.50
Enter quantity: 3

--- KOMPAS COFFEE HOUSE RECEIPT ---
Unit Price: RM 12.50
Quantity:   3 units
Subtotal:   RM 37.50
Tax (6%):   RM 2.25
Total Due:  RM 39.75

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