简单的GUI无法显示？

Question

好的，当我运行它时，它一切正常，但是并没有弹出答案。

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。 忘记了对它们进行记录，但是请参阅此代码以了解开始的修补程序。

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

您是否希望按下“确定”按钮时弹出答案框？ 如果是这样，则需要调用answer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，还需要执行其他一些操作：

• 通常，在向框架添加组件之后，应该在GUI构造方法的末尾调用JFrame.setVisible。 我已经在下面的示例中显示了这一点，但是您也应该将setVisible（..）移到AFwindow（）方法的底部。

• 当你做int area = (int) (length * width); 在任何方法之外，此语句将被解释为实例变量初始化，并且在实例化AF对象时发生。 并且当实例化对象时，您尚未为length和with分配任何值。 因此，区域将始终为0。将其移至答案函数的内部。

• 您忘记了在答案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，将仅显示一个空框架。

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

该代码对我有用：

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);
    }
}

我假设您可以尝试减少代码并尝试以这种方式查找问题点。 您可以放置​​一些日志记录以确保setVisible(true) 。 我也建议使用setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 在退出GUI后终止线程（如果不想执行某些退出后操作）。