GUI 读取 JTextField 时遇到问题

Question

我不知道我哪里出了问题，我尝试改变一些东西，但我就是无法让“CalculateButtonHandler”正常工作。抱歉，把所有这些代码都列出来，但上次我没有具体说明足够了：S 如果有人能指出我正确的方向，那就太好了。

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

// some kind of problem with Calculate button handler (LINE 78 

public class Program5 extends JFrame
{
    // Setting up for the program
    private JLabel side1, side2, side3, str, result;

    private JButton calculate, endProgram;

    private JTextField input1, input2, input3;

    private CalculateButtonHandler calcHandler;
    private EndProgramButtonHandler endHandler;

    private Container pane;

    private static final int WIDTH = 500;
    private static final int HEIGHT = 350;

    // constructor
    public Program5()
    {
        // create labels
        side1 = new JLabel ("Triangle's Longest Side: ", SwingConstants.CENTER);
        side2 = new JLabel ("Triangle's Next Side: ", SwingConstants.CENTER);
        side3 = new JLabel ("Triangle's Last Side: ", SwingConstants.CENTER);
        result = new JLabel ("", SwingConstants.CENTER);
        str = new JLabel ("Is the Triangle a right Triangle?",SwingConstants.CENTER);

        // create text fields
        input1 = new JTextField ("", 60);
        input1.setHorizontalAlignment(JTextField.CENTER);
        input2 = new JTextField ("", 60);
        input2.setHorizontalAlignment(JTextField.CENTER);
        input3 = new JTextField ("", 60);
        input3.setHorizontalAlignment(JTextField.CENTER);

        // create buttons
        calculate = new JButton ("Calculate");
        calcHandler = new CalculateButtonHandler ();
        calculate.addActionListener(calcHandler);

        endProgram = new JButton ("Exit");
        endHandler = new EndProgramButtonHandler();
        endProgram.addActionListener(endHandler);

        // Set title of Window
        setTitle ("Right Triangle Tester");

        //Get Container
        pane = getContentPane();

        // set Layout
        pane.setLayout (new GridLayout (5, 2));

        // place the components in the pane
        pane.add(side1);
        pane.add(input1);
        pane.add(side2);
        pane.add(input2);
        pane.add(side3);
        pane.add(input3);
        pane.add(str);
        pane.add(result);
        pane.add(calculate);
        pane.add(endProgram);

        // set size of the window and display it
        setSize (WIDTH, HEIGHT);
        setVisible (true);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);     
    }

    private class CalculateButtonHandler implements ActionListener
    {
        public void actionPerformed (ActionEvent e)
        {
            double num1, num2, num3;
            num1 = Double.parseDouble(side1.getText());
            num2 = Double.parseDouble(side2.getText());
            num3 = Double.parseDouble(side3.getText());

            if ((num1*num1) == ((num2*num2)+(num3*num3)))
            {
                result.setText("YES");
            }
            else
            {
            result.setText("NO");
            }
        }       
    }

    private class EndProgramButtonHandler implements ActionListener
    {
        public void actionPerformed (ActionEvent e)
        {
            System.exit(0);
        }
    }

    public static void main(String[] args)  
    {       
        Program5 myObject = new Program5();
    }
}

Answer 1

您正在解析 sideX 文本，它们是 JLabels，而不是 JTextField。将 CalculateButtonHandler 中的 sideX 替换为 inputX ，一切都会好起来的

Answer 2

1）使用 JFormattedTextField （witt 数字实例) 而不是普通的 JTextField，那么你无法解决从 String 解析 Number 实例的问题，

2）看起来像此代码解析来自 JLabels 而不是 JTextFields

Answer 3

在您使用 JLabel 获取输入的 CalculateButtonHandler 类中，似乎您需要 JTextField 来获取输入，将该类更改为：

private class CalculateButtonHandler implements ActionListener
{
    public void actionPerformed (ActionEvent e)
    {
        double num1, num2, num3;
        num1 = Double.parseDouble(input1.getText());
        num2 = Double.parseDouble(input2.getText());
        num3 = Double.parseDouble(input3.getText());

        if ((num1*num1) == ((num2*num2)+(num3*num3)))
        {
            result.setText("YES");
        }
        else
        {
            result.setText("NO");
        }
    }       
}

并且从下次开始始终安排作业对于事件调度程序线程，在使用 Swing（如您的情况）时，您的主要方法必须如下所示：

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

// some kind of problem with Calculate button handler (LINE 78 

public class Program5 extends JFrame
{
    // Setting up for the program
    private JLabel side1, side2, side3, str, result;

    private JButton calculate, endProgram;

    private JTextField input1, input2, input3;

    private CalculateButtonHandler calcHandler;
    private EndProgramButtonHandler endHandler;

    private Container pane;

    private static final int WIDTH = 500;
    private static final int HEIGHT = 350;

    // constructor
    public Program5()
    {
            // create labels
        side1 = new JLabel ("Triangle's Longest Side: ", SwingConstants.CENTER);
        side2 = new JLabel ("Triangle's Next Side: ", SwingConstants.CENTER);
        side3 = new JLabel ("Triangle's Last Side: ", SwingConstants.CENTER);
        result = new JLabel ("", SwingConstants.CENTER);
        str = new JLabel ("Is the Triangle a right Triangle?",SwingConstants.CENTER);


            // create text fields
        input1 = new JTextField ("",60);
        input1.setHorizontalAlignment(JTextField.CENTER);
        input2 = new JTextField ("",60);
        input2.setHorizontalAlignment(JTextField.CENTER);
        input3 = new JTextField ("",60);
        input3.setHorizontalAlignment(JTextField.CENTER);

        // create buttons
        calculate = new JButton ("Calculate");
        calcHandler = new CalculateButtonHandler ();
        calculate.addActionListener(calcHandler);

        endProgram = new JButton ("Exit");
        endHandler = new EndProgramButtonHandler();
        endProgram.addActionListener(endHandler);

        // Set title of Window
        setTitle ("Right Triangle Tester");

        //Get Container
        pane = getContentPane();

        // set Layout
        pane.setLayout (new GridLayout (5,2));

        // place the components in the pane
        pane.add(side1);
        pane.add(input1);
        pane.add(side2);
        pane.add(input2);
        pane.add(side3);
        pane.add(input3);
        pane.add(str);
        pane.add(result);
        pane.add(calculate);
        pane.add(endProgram);

        // set size of the window and display it
        setSize (WIDTH, HEIGHT);
        se1tVisible (true);
        setDefaultCloseOperation (EXIT_ON_CLOSE);       
    }

    private class CalculateButtonHandler implements ActionListener
    {
        public void actionPerformed (ActionEvent e)
        {
            double num1, num2, num3;
            num1 = Double.parseDouble(input1.getText());
            num2 = Double.parseDouble(input2.getText());
            num3 = Double.parseDouble(input3.getText());

            if ((num1*num1) == ((num2*num2)+(num3*num3)))
            {
                result.setText("YES");
            }
            else
            {
                result.setText("NO");
            }
        }       
    }

    private class EndProgramButtonHandler implements ActionListener
    {
        public void actionPerformed (ActionEvent e)
        {
            System.exit(0);
        }
    }

    public static void main(String[] args)  
    {
        // Here this is used to attain Concurrency in Swing.
        // So that if there is a need to update the GUI, 
        // that can be done without any difficulty or freezing the GUI.
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                Program5 myObject = new Program5();
            }
        });
    }
}

要了解更多关于我正在谈论的内容，请阅读 Swing 中的并发。关于 Swing 非常重要的事情在本章中。

Answer 4

您还直接比较双打。您不太可能认为这种比较是正确的。运行这个：

     double num1,num2,num3;
     num1=2.8284271247461903;   //== Math.sqrt(8) 
     num2=2.0; num3=2.0;
     if ((num1*num1) == ((num2*num2)+(num3*num3)))
         System.out.println  ("yes");
     else System.out.println  ("no " + num1*num1 + " " + (num2*num2 + num3*num3));


 }