程序的输出无法在 Java 中正确显示 [关闭]答案

【问题标题】：Output of program unable to display correctly in Java [closed]程序的输出无法在 Java 中正确显示 [关闭]
【发布时间】：2018-06-13 12:22:34
【问题描述】：

我正在尝试创建一个程序来计算学生的出勤率。程序计算得很好，但我的输出有问题。如果学生有 100% 的出勤率，程序将按预期显示百分比。但是当学生小于100%时，无论输入什么值，程序都会将百分比显示为0%。

图形用户界面的主要部分

class Frame extends JFrame
{
    private JButton calcButton;
    private JTextField daysPresentText;
    private JLabel instructionLabel;
    private JComboBox<String> intakeComboBox;
    private JLabel intakeLabel;
    private JLabel maxDaysLabel;
    private JComboBox<String> semesterComboBox;
    private JLabel semesterLabel;
    private JLabel statusLabel;
    private JLabel studentLabel;
    static JTextField studentText;

    String semester, intake, daysPresent, semesterLength;
    int maxDays, days;
    static double attendancePercentage;

    public Frame() 
    {
       initComponents();


    }

     @SuppressWarnings("unchecked")                         
    private void initComponents() 
    {

        studentText = new JTextField();
        instructionLabel = new JLabel();
        statusLabel = new JLabel();
        semesterLabel = new JLabel();
        studentLabel = new JLabel();
        calcButton = new JButton();
        semesterComboBox = new JComboBox<>();
        daysPresentText = new JTextField();
        maxDaysLabel = new JLabel();
        intakeLabel = new JLabel();
        intakeComboBox = new JComboBox<>();

        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        instructionLabel.setText("Enter student name and days present");

        statusLabel.setText("Days Present");

        semesterLabel.setText("Semester");

        studentLabel.setText("Student");

        calcButton.setText("Calculate Percentage");
        calcButton.addActionListener(new ActionListener() 
        {
            public void actionPerformed(ActionEvent evt) 
            {
                calcButtonActionPerformed(evt);
            }
        });

        semesterComboBox.setModel(new DefaultComboBoxModel<>(new String[] { "1", "2", "3", "4", "5","6","7"}));
        semesterComboBox.addItemListener(new ItemListener() 
        {
            public void itemStateChanged(ItemEvent evt) 
            {
                semesterComboBoxItemStateChanged(evt);
            }
        });

        daysPresentText.setText("");

        intakeLabel.setText("Intake");

        intakeComboBox.setModel(new DefaultComboBoxModel<>(new String[] { "March", "August"}));
        intakeComboBox.addItemListener(new ItemListener() 
        {
            public void itemStateChanged(ItemEvent evt) 
            {
                intakeComboBoxItemStateChanged(evt);
            }
        });

        GroupLayout layout = new GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap(GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING, false)
                    .addComponent(studentLabel, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                    .addComponent(instructionLabel, GroupLayout.DEFAULT_SIZE, 257, Short.MAX_VALUE)
                    .addComponent(studentText))
                .addGap(18, 18, 18)
                .addGroup(layout.createParallelGroup(GroupLayout.Alignment.TRAILING)
                    .addGroup(layout.createSequentialGroup()
                        .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING, false)
                            .addGroup(layout.createSequentialGroup()
                                .addComponent(semesterComboBox, GroupLayout.PREFERRED_SIZE, 113, GroupLayout.PREFERRED_SIZE)
                                .addGap(18, 18, 18)
                                .addComponent(intakeComboBox, GroupLayout.PREFERRED_SIZE, 96, GroupLayout.PREFERRED_SIZE))
                            .addGroup(layout.createSequentialGroup()
                                .addComponent(semesterLabel, GroupLayout.PREFERRED_SIZE, 113, GroupLayout.PREFERRED_SIZE)
                                .addGap(18, 18, 18)
                                .addComponent(intakeLabel, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)))
                        .addPreferredGap(LayoutStyle.ComponentPlacement.RELATED)
                        .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING, false)
                            .addGroup(layout.createSequentialGroup()
                                .addComponent(daysPresentText, GroupLayout.PREFERRED_SIZE, 95, GroupLayout.PREFERRED_SIZE)
                                .addPreferredGap(LayoutStyle.ComponentPlacement.RELATED)
                                .addComponent(maxDaysLabel, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
                            .addComponent(statusLabel, GroupLayout.PREFERRED_SIZE, 184, GroupLayout.PREFERRED_SIZE)))
                    .addComponent(calcButton, GroupLayout.PREFERRED_SIZE, 198, GroupLayout.PREFERRED_SIZE))
                .addGap(30, 30, 30))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(instructionLabel, GroupLayout.PREFERRED_SIZE, 44, GroupLayout.PREFERRED_SIZE)
                .addGap(20, 20, 20)
                .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE)
                            .addComponent(statusLabel, GroupLayout.PREFERRED_SIZE, 58, GroupLayout.PREFERRED_SIZE)
                            .addComponent(intakeLabel, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
                        .addPreferredGap(LayoutStyle.ComponentPlacement.UNRELATED)
                        .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING, false)
                            .addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE)
                                .addComponent(intakeComboBox, GroupLayout.PREFERRED_SIZE, 46, GroupLayout.PREFERRED_SIZE)
                                .addComponent(daysPresentText, GroupLayout.PREFERRED_SIZE, 46, GroupLayout.PREFERRED_SIZE))
                            .addComponent(studentText)
                            .addComponent(semesterComboBox)
                            .addComponent(maxDaysLabel, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)))
                    .addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE)
                        .addComponent(studentLabel, GroupLayout.PREFERRED_SIZE, 58, GroupLayout.PREFERRED_SIZE)
                        .addComponent(semesterLabel, GroupLayout.PREFERRED_SIZE, 58, GroupLayout.PREFERRED_SIZE)))
                .addGap(18, 18, 18)
                .addComponent(calcButton, GroupLayout.PREFERRED_SIZE, 63, GroupLayout.PREFERRED_SIZE)
                .addContainerGap())
        );

        pack();
    }     

    private void semesterComboBoxItemStateChanged(ItemEvent evt) 
    {     
     semester=evt.getItem().toString();
    }                                                 

    private void intakeComboBoxItemStateChanged(ItemEvent evt) 
    {                                                
     intake=evt.getItem().toString();
    }

    private void calcButtonActionPerformed(ActionEvent evt)
    {
       daysPresent=daysPresentText.getText();       
       days=Integer.valueOf(daysPresent);
        maxDays=98;
        if(days>maxDays)
        {
          errorMessage EM=new errorMessage();
          EM.setVisible(true);
        }else
        {
        calculate();
        CalculateDisplay CD=new CalculateDisplay();
        CD.setVisible(true);
        }
    }                      


    public void calculate()
    {
        attendancePercentage=(days/maxDays)*100;
    }
}

方程输出的显示

   class CalculateDisplay extends JFrame 
{
    private JLabel displayLabel;
    private JButton okButton;

    String student;
    double attendancePercentage;

    public CalculateDisplay() 
    {
        initComponents();
        student=Frame.studentText.getText();
        attendancePercentage=Frame.attendancePercentage;
        displayLabel.setText("The attendance percentage of "+student+" is 
        "+attendancePercentage+".");
    }

【问题讨论】：

即使没有阅读您提供的大量代码，这听起来像是一个整数除法问题，请确保您的百分比计算中提供的数字之一是浮点/小数类型
Too... much... code... 将事情缩小到本质，这是包括计算在内的几行代码，其中包含整数除法。简单的调试或日志记录会告诉你这一点。
你调试过你的代码吗？看到您发布的大部分代码都是 Netbeans 生成的 Swing 代码，我假设您使用的是包含调试器的 IDE
Why is the result of 1/3 == 0?的可能重复
attendancePercentage=(days/maxDays)*100; 和 int maxDays, days; @NickA 是对的

标签： java output

【解决方案1】：

这是一个基本的整数除法问题Integer division: How do you produce a double?

要么将int maxDays, days; 更改为double maxDays, days;，要么将您的计算方法更改为：

attendancePercentage=(days/maxDays)*100;

到：

attendancePercentage = ((double) days / (double) maxDays) * 100;`

【讨论】：