Java 程序产生不正确的输出。 (while 循环)

Question

Here is a sample of what output should look like!!

我的用于显示已购买笔记本电脑的订单摘要的程序使用 (1)while 循环来处理多台笔记本电脑，使用 (2)if-else 来获取笔记本电脑名称/价格；或错误消息“无效选择!请重试。”，(3) 嵌套 if 以确定笔记本电脑的选择何时有效以继续其余处理。以及 (4) 嵌套 if 仅在购买笔记本电脑时打印订单摘要。

当我在 choice 中输入无效数字(如 8)时，if 语句仍然执行，而不是其下面的 else 语句。
当我在 choice 中输入有效数字时，它会要求输入数量，但是当我输入数量时，如何将该用户输入添加到订单摘要中，而不是让程序返回到循环顶部？

我对 Java 很陌生，我的代码应该如何生成正确的输出？

这是我当前的代码(JAVA)

public static void main(String[] args) { 
    char cont='Y';
    int qty=0;
    int trigger=0;

    double total=0;
    double subtotal=0;
    double tax=0;
    double price;
    double lineItem=0;

    String orderSummary=" ";
    String laptop=" ";
    Scanner input = new Scanner(System.in);
    Calendar dateTime = Calendar.getInstance();

    //Displays a list of laptops with prices and asked user for their choice. Prompt #1
    int choice = 0;

    while (choice >= 0) {  
        System.out.printf("%nTOP LAPTOPS OF %tY"
                        + "%n%n1. %-23s %7s $%,9.2f"
                        + "%n2. %-23s %8s %,9.2f"
                        + "%n3. %-23s %8s %,9.2f"
                        + "%n4. %-23s %8s %,9.2f"
                        + "%n5. %-23s %8s %,9.2f"
                        + "%n%nEnter your choice: ",
                      dateTime,
                      "HP Envy 13", " ", 799.99, 
                      "Asus ZenBook 13 UX333FA", " ", 849.99,
                      "Dell XPS 13", " ", 989.99,
                      "Alienware Area 51-m", " ", 1999.99,
                      "Razer Blade Stealth", " ", 1299.00);

        choice = input.nextInt();

        if (choice < 6 || choice > 0) {
          System.out.printf("Enter the quantity:");
          qty = input.nextInt();
        } else {
          System.out.printf("Invalid choice! Try again.%n%n");
          System.out.printf("Enter 'Y' to add a laptop to your purchase or 'N' to exit: ");
          cont = input.next().charAt(0);
        }
        if (cont == 'Y') {
          continue;
        }
        if (cont == 'N') {
          System.exit(0);
        }

        //The following if-else prints a $ sign for the first line item
        if (trigger == 1) {
          orderSummary += String.format("%n%, -9d %-30s %8s $%,17.2f", qty, laptop, " ", lineItem);
          trigger = 0;
        } //End else for no $ sign

        //The following statement prints the order summary of the laptops purchased.
        //This should be done when there are no more laptops to process
        if (choice > 0) {
            if (choice < 6) {
                tax = subtotal * .0825;
                total = subtotal + tax;

                orderSummary += String.format("%n%n%34s Subtotal %6s %,17.2f"
                                            + "%n%31s Tax @ 8.25%% %6s %,17.2f"
                                            + "%n%n%37s TOTAL %5s $%,17.2f%n",
                                          " ", " ", subtotal,
                                          " ", " ", tax,
                                          " ", " ", total);
                System.out.printf("%s", orderSummary);
                break;
            } //End if valid choice range ends print order summary  
        } //End if valid choice range begins
    }
} 

Answer 1

因为语句规则 AND (&&) OR (&&) 对应于 boolean 代数。

if(选择 < 6 || 选择 > 0)对应于“如果选择为 <8”为真，或者如果“选择 > 0”为真，则整个表达式为真

例如，对于选定的 8 个，它将为 TRUE，因此其他情况不会发生

尝试 if (选择 > 0 && 选择 <6)

然后思考“业务逻辑”，准备存储和重用，组织变量进行计算，请参见下面的示例

import java.util.*;

public class Example{
public static void main(String[] args) {


String [] product = {"HP Envy 13","Asus ZenBook 13 UX333FA","Dell XPS 13","Alienware Area 51-m","Razer Blade Stealth"};
double [] unit_rate = {799.99, 849.99, 989.99, 1999.99, 1299.00};
int [] user_selectected_qty = new int [product.length]; 

double total = 0;
boolean again = true;

Scanner input = new Scanner(System.in);
int choice,qty;

while (again)
{

    System.out.println("TOP LAPTOPS");
    for(int i=1; i<product.length ; i++)
        System.out.println(""+i+".\t"+product[i]+"\t\t\t"+unit_rate[i]);

    System.out.println("Enter your choice:");
    choice = input.nextInt();

    // SELECTION PROCESS
    if (choice >0 && choice <6)
    {
    System.out.println("Enter the quantity for "+product[choice]+":");
    qty = input.nextInt();
    user_selectected_qty[choice]+=qty;  


    // ... ASK TO DO IT AGAIN...


    again=false;

    }
    else
    {
     System.out.println("Wrong choice:");
    }

}
    // BEFORE END SHOW SUMMARY  ...COMPUTE TOTAL ...
    System.out.println("LAPTOP ORDER SUMARY");

    for(int i=1; i<product.length ; i++)
        if (user_selectected_qty[i] > 0)
            System.out.println(""+user_selectected_qty[i]+"\t"+product[i]+"\t\t\t"+unit_rate[i]*user_selectected_qty[i]);





}
}