java - 如何让我的程序将其覆盖的产品销售额百分比更新为 100%

Question

基本上，我的程序获取销售值并进行更新。该程序还应该更新该产品占所有产品总销售额的 100% 的百分比。例如，如果我输入胡萝卜的销量为 100，那么所有销量的百分比应为 100%，因为这是唯一已售出的产品，并且只有 100 的销量。当您添加大约 100 份土 bean 销售额时，每个土 bean 的百分比将更改为 50%，因为两者之间有 200 份销售额。我该如何编码才能发生这种情况。我尝试的代码附在下面，任何其他问题请在下面评论。

问题出在calculatepercentage方法和updatesalesaction方法中以百分比开头的语句中。当我将销售额添加到特定产品时，百分比没有更新

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

/**
This is an initial starter version of a Java application that should be
extended in stages, eventually allowing the user to enter product sales figures
for a number of products, and display them in a table with %ages, a ranking and a pie chart.

This starter code just has storage for one product, and allows that product's sales figure 
to be updated and displayed. The display is plain, with no font changes and
no border lines for the table. All the processing is limited to just this one product,
and must be adapted for a whole array of products.

SBJ March 2016
 */

public class ProductChart extends JFrame implements ActionListener
{
    /**
     * Frame constants
     */
    private static final int FRAME_LOCATION_X = 350;
    private static final int FRAME_LOCATION_Y = 250;
    private static final int FRAME_WIDTH = 650;
    private static final int FRAME_HEIGHT = 400;

    /**
     * The maximum permitted number of products
     */
    private final int MAX_PRODUCTS = 10;

    /**
     * These arrays holds all the sales data:
     * Element 0 is unused, so array sizes are MAX_PRODUCTS+1.
     * The product number (from 1 to MAX_PRODUCTS) is the index in the arrays
     * where the product's data is held. 
     * Sales figures are counted quantities, so int.
     */
    private String[] productName;  // The name of each product
    private int[] productSales;    // The number of sales of each product
    private float[] percentage;    // The proportion of total sales for each product

    private int totalSales;        // Always the current total sales

    /**
     * Display area layout constants
     */
    private final int DISPLAY_WIDTH = 600;
    private final int DISPLAY_HEIGHT = 300;
    private final int PRODUCT_X = 30;   // Start of product number column
    private final int NAME_X = 75;      // Start of product name column
    private final int SALES_X = 225;    // Start of sales column
    private final int PERCENTAGE_X = 300;    //Start of percentage column
    private final int TABLE_LINES_Y = 12; //The number of horizontal lines required to draw the table
    private final int TABLE_LINES_X = 5; //The number of vertical ""

    /**
     * The main launcher method:
     * Configure the applications's window, initialize the sales data structures,
     * and make the applications visible.
     * @param args Unused
     */
    public static void main(String[] args)
    {
        ProductChart frame = new ProductChart();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocation(FRAME_LOCATION_X, FRAME_LOCATION_Y);
        frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
        frame.initializeSalesData();
        frame.createGUI();
        frame.setVisible(true);
        frame.setTitle("Product Chart 2312931");

    }

    /**
     * The GUI components
     */
    private JTextField productSalesEntryField;  // For entry of new product sales figures
    private JButton updateSalesButton;          // To request update of a sales figure
    private JPanel displayArea;                 // Graphics area for drawing the sales table
    private JTextField productRefEntryField;    // For entry of product refence number when updating sales figures

    /**
     * Helper method to build the GUI
     */
    private void createGUI()
    {
        // Standard window set up
        Container window = getContentPane();
        window.setLayout(new FlowLayout());
        window.setBackground(Color.lightGray);

        // Product reference entry label and text field
        JLabel productRefEntryLabel = new JLabel("Product Ref #:");
        productRefEntryField = new JTextField(2);
        window.add(productRefEntryLabel);
        window.add(productRefEntryField);       

        // Product sales entry label and text field
        JLabel productSalesEntryLabel = new JLabel("Product sales:");
        productSalesEntryField = new JTextField(5);
        window.add(productSalesEntryLabel);
        window.add(productSalesEntryField);

        // Button to add new sales figure
        updateSalesButton = new JButton("Update sales");
        updateSalesButton.addActionListener(this);
        window.add(updateSalesButton);

        // The drawing area for displaying all data
        displayArea = new JPanel()
        {
            // paintComponent is called automatically when a screen refresh is needed
            public void paintComponent(Graphics g)
            {
                // g is a cleared panel area
                super.paintComponent(g); // Paint the panel's background
                paintScreen(g);          // Then the required graphics
            }
        };
        displayArea.setPreferredSize(new Dimension(DISPLAY_WIDTH, DISPLAY_HEIGHT));
        displayArea.setBackground(Color.white);
        window.add(displayArea);
    }

    /**
     * Initializes product arrays:
     * A set of product names,
     * With sales initially 0.
     * 
     * Note: In the arrays, the first element is unused, so Bread is at index 1
     */
    private void initializeSalesData()
    {
        productName = new String[MAX_PRODUCTS+1];
        productName[1] = "Bread";   // Note: First element is unused, so Bread is at index 1
        productName[2] = "Milk";
        productName[3] = "Eggs";
        productName[4] = "Cheese";
        productName[5] = "Cream";
        productName[6] = "Butter";
        productName[7] = "Jam";
        productName[8] = "Chocolate Spread";
        productName[9] = "Corn Flakes";
        productName[10] = "Sugar";

        productSales = new int[MAX_PRODUCTS+1];
        for(int i=0; i< MAX_PRODUCTS; i++)
        {
            productSales[i] = 0;
        }

        percentage = new float[MAX_PRODUCTS+1];
        for(int i=0; i< MAX_PRODUCTS; i++)
        {
            percentage[i] = 0;
        }

    }

    /**
     * Event handler for button clicks.
     *
     * One action so far:
     * o Update the sales figure for a product
     */
    public void actionPerformed(ActionEvent event)
    {
        if (event.getSource() == updateSalesButton)
            updateSalesAction();

        // And refresh the display
        repaint();
    }

    /**
     * Action updating a sales figure: the new sales figure is fetched 
     * from a text fields, parsed (converted to an int), and action is taken.
     */
    private void updateSalesAction()
    {
        // Fetch the new sales details
        int productRef = Integer.parseInt(productRefEntryField.getText());
        int newSales = Integer.parseInt(productSalesEntryField.getText());
        if (productRef>0&&productRef<=MAX_PRODUCTS)
        {
            // Update the sales tables
            productSales[productRef] = newSales;
            totalSales = totalSales + newSales;
            percentage[productRef] = calculatePercentage(productSales[productRef-1], totalSales); 
        }


    }

    /**
     * Redraw all the sales data on the given graphics area
     */
    public void paintScreen(Graphics g)
    {
        // Draw a table of the sales data, with columns for the product number,
        // product name, and sales

        //Heading
        g.setFont(new Font("default", Font.BOLD, 16));
        g.drawString("Product sales data:", 20, 20);

        // Table column headers
        g.setFont(new Font("default", Font.BOLD, 12));
        g.drawString("No", PRODUCT_X, 60);
        g.drawString("Name", NAME_X, 60);
        g.drawString("Sales", SALES_X, 60);
        g.drawString("Percentage", PERCENTAGE_X, 60);

        // The table of sales data
        g.setFont(new Font("default", Font.PLAIN, 12));
        int y = 80;// The y coordinate for each line
        int yIncrement = 20;

        for(int i = 0; i<productName.length-1; i++)
        {
            g.drawString(""+Integer.toString(i+1), PRODUCT_X, y+i*yIncrement);          // First column: product number

        }
        for(int i = 0; i<productName.length-1; i++)
        {
            g.drawString(productName[i+1], NAME_X, y+i*yIncrement);    // Second column: product name

        }
        for(int i = 0; i<productSales.length-1; i++)
        {
            g.drawString(Integer.toString(productSales[i+1]), SALES_X, y+i*yIncrement); // Third column: sales figure 
        }
        for(int i = 0; i<percentage.length-1; i++)
        {
            g.drawString(Float.toString(percentage[i+1]), PERCENTAGE_X, y+i*yIncrement);
        }
        for(int i = 0; i<TABLE_LINES_Y ; i++)
        {
            //g.drawLine(
        }
    }

    public float calculatePercentage(int sales, int totalSales)
    {
        float percentage = sales/totalSales;
        return percentage;     

    }
}

Answer 1

首先，您的百分比计算受到整数除法的影响，因此它总是四舍五入到最接近的整数。使用它来计算您的百分比(另外，乘以 100，使其看起来更像百分比):

public float calculatePercentage(int sales, int totalSales)
{
    return 100.0f * sales / totalSales;
}

其次，您需要在每次更新时循环遍历所有产品，以便所有百分比都准确，并且totalSales计数也准确。

private void updateSalesAction()
{
    // Fetch the new sales details
    int productRef = Integer.parseInt(productRefEntryField.getText());
    int newSales = Integer.parseInt(productSalesEntryField.getText());
    if (productRef>0&&productRef<=MAX_PRODUCTS)
    {
        // Update the sales tables
        productSales[productRef] = newSales;
        totalSales = 0;
        for (int i = 1; i <= MAX_PRODUCTS; i++)
            totalSales += productSales[i];
        for (int i = 1; i <= MAX_PRODUCTS; i++)
            percentage[i] = calculatePercentage(productSales[i], totalSales);
    }
}

我测试了它，这些更新修复了程序。