java - 添加以前的值（java）？

Question

我有一个购物清单，根据用户给我的值，我必须更新总数。例如：

您可能已经注意到总数每次都会更新，我该如何在我的代码中做到这一点？

这就是我所拥有的：

public class CalcGroceryList {
private double productOne;
private double productTwo;
private double productThree;
private double productFour;
private double productFive;
private int n++;

public CalcGroceryList(){
    Scanner in = new Scanner(System.in);
    System.out.println("Enter price of first item:");
    productOne = in.nextDouble();
    System.out.println("Enter price of second item:");
    productTwo = in.nextDouble();
    System.out.println("Enter price of third item:");
    productThree = in.nextDouble();
    System.out.println("Enter price of fourth item:");
    productFour = in.nextDouble();
    System.out.println("Enter price of fifth item:");
    productFive = in.nextDouble();
}

public double calc(){
    return productOne + productTwo + productThree + productFour + productFive;
}

public void printResults(){
    System.out.printf("%10s %10s %10s \n", "Item:", "Cost:", "Price:");
    System.out.printf("%10d %10.2f %10.2f \n", n++ ,productOne, productOne);
    System.out.printf("%10d %10.2f %10.2f", n++ ,productTwo, productTwo + productOne);  
}

}

System.out.printf("%10d %10.2f %10.2f", n++ ,productTwo, productTwo + productOne); 

正如您在此处看到的，我只是添加了两个值（productTwo + productOne），但是有没有一种方法可以在不指定确切值的情况下执行此操作，例如，每次添加我们拥有的所有当前值。

Answer 1

Scanner in = new Scanner(System.in);
    System.out.println("Enter price of first item:");
    product = in.nextDouble();
    System.out.println("Enter price of second item:");
    product += in.nextDouble();
    System.out.println("Enter price of third item:");
    product += in.nextDouble();
    System.out.println("Enter price of fourth item:");
    product += in.nextDouble();
    System.out.println("Enter price of fifth item:");
    product += in.nextDouble();

有更好的方法，但只是让你目前拥有的东西更容易就是这样。

Answer 2

您可以简单地创建一个变量来保存项目的总值，并且每次用户向列表中添加一个值时，它使用+=运算符添加到总数中。例如：

private double total;

添加到总数：

System.out.println("Enter price of second item:");
productTwo = in.nextDouble();
total += productTwo;
//call a method here to print the values to the table

用于打印值：

System.out.printf("%10d %10.2f %10.2f", n++ ,productTwo, total); 

Answer 3

您可以使用ArrayList

ArrayList<Double> costArray = new ArrayList<Double>();
double cost;

System.out.println("Enter price of first item:");
cost = in.nextDouble();
costArray.add(cost);
System.out.println("Enter price of second item:");
cost = in.nextDouble();
costArray.add(cost);
System.out.println("Enter price of third item:");
cost = in.nextDouble();
costArray.add(cost);
System.out.println("Enter price of fourth item:");
cost = in.nextDouble()
costArray.add(cost);
System.out.println("Enter price of fifth item:");
product += in.nextDouble();
costArray.add(cost);

double total = 0;
for (int i = 1; i <= costArray.length; i++) {
    total += costArray[i];
    System.out.printf("%10s %10.2f %10.2f", "#" + i, costArray[i], total);
}

total += costArray[i]是一样的total = total + castArray[i]。