Question

我有一份我编写的家庭作业。我以为我已经完成了它，但每当我想显示平均值时，它会在内容窗格中显示0的列表。

以下是作业的说明。

编写一个Swing程序，用a声明一个空的成绩数组   最大长度为50.一段时间内实现一个JOptionPane输入框   循环以允许用户输入成绩。当用户输入时   sentinel值为-1，表示数据输入循环结束。

输入成绩后，内容窗格应显示成绩   从最低到最高排序。写一个循环通过   数组寻找大于零（0）的元素。保持一个   运行这些项目的计数，并将它们累积成盛大的   总。将总计除以输入的等级数来查找   平均值，并显示排序列表末尾的平均值   等级。使用DecimalFormat方法将平均值显示为2   小数位。

/*
    Chapter 7:      Average of grades
    Programmer:     
    Date:           
    Filename:       Averages.java
    Purpose:        To use the Java Swing interface to calculate the average of up to 50 grades.
                    Average is calculated once -1 is entered as a value. The grades are then sorted
                    from lowest to highest and displayed in a content pane which also displayes the average.
*/

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

public class Averages extends JFrame
{
    //construct conponents
    static JLabel title = new JLabel("Average of Grades");
    static JTextPane textPane = new JTextPane();
    static int numberOfGrades = 0;
    static int total = 0;
    static DecimalFormat twoDigits = new DecimalFormat ("##0.00");

    //set array
    static int[] grades = new int[50];

    //create content pane
    public Container createContentPane()
    {
        //create JTextPane and center panel
        JPanel northPanel = new JPanel();
        northPanel.setLayout(new FlowLayout());
        northPanel.add(title);

        JPanel centerPanel = new JPanel();
        textPane = addTextToPane();
        JScrollPane scrollPane = new JScrollPane(textPane);
            scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
            scrollPane.setPreferredSize(new Dimension(500,200));
        centerPanel.add(scrollPane);

        //create Container and set attributes
        Container c = getContentPane();
            c.setLayout(new BorderLayout(10,10));
            c.add(northPanel,BorderLayout.NORTH);
            c.add(centerPanel,BorderLayout.CENTER);

        return c;
    }

    //method to add new text to JTextPane
    public static JTextPane addTextToPane()
    {
        Document doc = textPane.getDocument();
        try
        {
            // clear previous text
            doc.remove(0,doc.getLength());

            //insert title
            doc.insertString(0,"Grades\n",textPane.getStyle("large"));

            //insert grades and calculate average
            for(int j=0; j<grades.length; j++)
            {
                doc.insertString(doc.getLength(), grades[j] + "\n", textPane.getStyle("large"));
            }
        }
        catch(BadLocationException ble)
        {
            System.err.println("Couldn't insert text");
        }

        return textPane;
    }

    //method to sort array
    public void grades(int grdArray[])
    {
        //sort int array
        for (int pass = 1; pass<grdArray.length; pass++)
        {
            for (int element = 0; element<grdArray.length -1; element++)
            {
                swap(grades, element, element + 1);

            }
        }
            addTextToPane();

    }


    //method to swap elements of array
    public void swap(int swapArray[], int first, int second)
    {
        int hold;
        hold = swapArray[first];
        swapArray[first] = swapArray[second];
        swapArray[second] = hold;
    }

    //execute method at run time
    public static void main(String args[])
    {
        JFrame.setDefaultLookAndFeelDecorated(true);
        Averages f = new Averages();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);


        //accept first grade
        int integerInput = Integer.parseInt(JOptionPane.showInputDialog(null, "Please enter a grade (0-100) or -1 to calculate the average"));

        //while loop accepts more grades, keeps count, and calulates the total
        int count = 0;
        int[] grades = new int[50];
        int num = 0;
        while (count<50 && num!= -1)
        {
            num = Integer.parseInt(JOptionPane.showInputDialog(null, "Please enter a grade (0-100) or -1 to calculate the average" + (count+1)));
            if(num!=-1)
                grades[count] = num;
            count++;

        }

        //create content pane
        f.setContentPane(f.createContentPane());
        f.setSize(600,375);
        f.setVisible(true);


    }
}

Answer 1

请解决问题。

从统计数据开始：

/**
 * Statistics
 * @author Michael
 * @link http://stackoverflow.com/questions/15626262/averaging-grades-using-java-swing?noredirect=1#comment22167503_15626262
 * @since 3/25/13 7:50 PM
 */
public class Statistics {
    public static double getAverage(int numValues, int [] values) {
        double average = 0.0;
        if ((values != null) && (numValues > 0) && (values.length >= numValues)) {
            for (int i = 0; i < numValues; ++i) {
                average += values[i];
            }
            average /= numValues;
        }
        return average;
    }
}

接下来我建议你将Swing完全抛弃一段时间。做一个纯文本输入/输出UI。

import java.util.Scanner;



/**
 * StatisticsDriver
 * @author Michael
 * @link http://stackoverflow.com/questions/15626262/averaging-grades-using-java-swing?noredirect=1#comment22167503_15626262
 * @since 3/25/13 7:50 PM
 */
public class StatisticsDriver {
    public static final int MAX_VALUES = 50;

    public static void main(String [] args) {
        int [] values = new int[MAX_VALUES];
        Scanner scanner = new Scanner(System.in);
        boolean getAnotherValue;
        int numValues = 0;
        do {
            System.out.print("next value: ");
            String input = scanner.nextLine();
            if (input != null) {
                values[numValues++] = Integer.valueOf(input.trim());
            }
            System.out.print("another? [y/n]: ");
            input = scanner.nextLine();
            getAnotherValue = "y".equalsIgnoreCase(input);
        } while (getAnotherValue);
        System.out.println(Statistics.getAverage(numValues, values));
    }
}

现在有了这些，请将注意力转向Swing。

在解决问题之前，太多的年轻程序员在Swing上缠绕在轴上。不要犯那个错误。

Answer 2

你已经声明了两次grades数组。一次在main()内，第二次在全球范围内。当您要求用户输入成绩时，您可以在main()内为阵列分配各种位置。但是，当您获得addTextToPane()中的信息时，您将调用全局声明的grades数组。

删除main()中的以下内容后，问题就解决了。

int[] grades = new int[50];

Answer 3

嗯，我能看到的第一个错误是：

您隐藏了主

中的静态数组成绩

int [] grades = new int [50];

使用Java Swing平均成绩

3 个答案: