Question

好的，当我运行它时，它运行良好，但它没有弹出答案。

我做错了什么？

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

public class AF implements ActionListener{

    double length;
    double width;
    double answer;

    JTextField twidth;
    JTextField tlength;

    void AFWindow() {

        JFrame AFwindow = new JFrame();
        JPanel pan2 = new JPanel(new GridBagLayout());
        AFwindow.setVisible(true);
        AFwindow.setSize(250, 150);
        AFwindow.setResizable(false);
        GridBagConstraints c = new GridBagConstraints();
        AFwindow.add(pan2);
        pan2.setBackground(Color.LIGHT_GRAY);

        c.gridx = 0;
        c.gridy = 5;
        tlength = new JTextField();
        tlength.setText("    Length    ");
        pan2.add(tlength, c);

        c.gridx = 0;
        c.gridy = 0;
        twidth = new JTextField();
        twidth.setText("     Width     ");
        pan2.add(twidth, c);

        JButton Find = new JButton("Ok");

        c.gridx = 0;
        c.gridy = -5;
        pan2.add(Find);
        Find.addActionListener(this);
        Find.setActionCommand("ok");
    }

    public void actionPerformed(ActionEvent e) {
        if (e.getActionCommand().equalsIgnoreCase("ok")){
            try {
            this.length = Double.parseDouble(tlength.getText());
            this.width = Double.parseDouble(twidth.getText());
        }
        catch(NumberFormatException ex){
            System.out.println("There was an issue!");
        }
        }
    }

    int area = (int) (length * width);
    public void answer(){
        JFrame answer = new JFrame();
        answer.setVisible(true);
        answer.setBackground(Color.yellow);
        JPanel pan2 = new JPanel();
        JLabel howanswer = new JLabel("Your answer is" + area + "We got this by multiplying the length and width");
        pan2.add(howanswer);
    }
}

Answer 1

该代码有多个问题。忘了记录它们，但是看看这段代码是否有修复的开头。

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
import javax.swing.border.EmptyBorder;

public class AF implements ActionListener{

    double length;
    double width;

    JTextField twidth;
    JTextField tlength;
    JFrame AFwindow;

    void AFWindow() {

        AFwindow = new JFrame();
        JPanel pan2 = new JPanel(new GridBagLayout());

        GridBagConstraints c = new GridBagConstraints();
        AFwindow.add(pan2);
        pan2.setBackground(Color.LIGHT_GRAY);
        pan2.setBorder(new EmptyBorder(100,100,100,100));

        c.gridx = 0;
        c.gridy = 5;
        tlength = new JTextField();
        tlength.setText("    Length    ");
        pan2.add(tlength, c);

        c.gridx = 0;
        c.gridy = 0;
        twidth = new JTextField();
        twidth.setText("     Width     ");
        pan2.add(twidth, c);

        JButton Find = new JButton("Ok");

        c.gridx = 0;
        c.gridy = -5;
        pan2.add(Find);
        Find.addActionListener(this);
        Find.setActionCommand("ok");
        AFwindow.pack();
        AFwindow.setLocationByPlatform(true);
        AFwindow.setVisible(true);
    }

    int area;

    public void actionPerformed(ActionEvent e) {
        if (e.getActionCommand().equalsIgnoreCase("ok")){
            try {
                this.length = Double.parseDouble(tlength.getText());
                this.width = Double.parseDouble(twidth.getText());
                area = (int) (length * width);
                answer();
            }
            catch(NumberFormatException ex){
                ex.printStackTrace();
                // System.out.println("There was an issue!");
                // Can you vague that up for me?!?!
                JOptionPane.showMessageDialog(AFwindow, ex);
            }
        }
    }

    public void answer(){
        JPanel pan2 = new JPanel();
        JLabel howanswer = new JLabel("Your answer is " + area + " We got this by multiplying the length and width");
        pan2.add(howanswer);
        JOptionPane.showMessageDialog(AFwindow, pan2);
    }

    public static void main(String[] args) {
        System.out.println("Hi!");
        new AF().AFWindow();
    }
}

Answer 2

按下“确定”按钮时，您是否希望弹出答案框？如果是这样，您需要调用答案方法：

    if (e.getActionCommand().equalsIgnoreCase("ok")){
        try {
            this.length = Double.parseDouble(tlength.getText());
            this.width = Double.parseDouble(twidth.getText());
            answer();       //  <--- This is missing
        }

此外，您还需要做一些其他事情：

通常，在向框架添加组件后，应在GUI构造方法的末尾调用JFrame.setVisible。我在下面的示例中已经显示了这一点，但您也应该将setVisible（..）移动到AFwindow（）方法的底部。
当您在任何方法之外执行int area = (int) (length * width);时，此语句将被解释为实例变量初始化，并在您实例化AF对象时发生。当对象被实例化时，您还没有为length指定任何值。因此，区域将始终为0.将该语句移动到答案函数的内部。
您忘记在answer方法中将实际组件添加到框架中。因此，当您将框架设置为可见时，只会显示一个空框架。

以下是一些适当更改的示例：

public void answer(){
    int area = (int) (length * width);  //  <--- Move this inside answer method
    JFrame answer = new JFrame();
    answer.setBackground(Color.yellow);
    JPanel pan2 = new JPanel();
    JLabel howanswer = new JLabel("Your answer is" + area + "We got this by multiplying the length and width");
    pan2.add(howanswer);
    answer.add(pan2); //  <--- Don't forget to add your components to the frame
    answer.pack();    //  <--- Resize the frame to a suitable size
    answer.setVisible(true); //  <--- Set the frame to visible AFTER you have added the components

}

Answer 3

此代码适用于我：

public class Test {
    public static void main(String[] args){
        JFrame test = new JFrame();
        test.setVisible(true);
        test.setSize(100,100);
        test.setResizable(false);
        test.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}

我认为您可以尝试减少代码并尝试以这种方式找到问题点。您可以进行一些日志记录以确保调用setVisible(true)。此外，我建议在退出GUI后使用setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);终止线程（如果不想执行某些退出后操作）。

简单的GUI没有出现？

3 个答案: