在重新调整窗口大小之前，图像不会出现

Question

我是Java和Swing的新手，所以我想尝试一些应用来实践它。在其中，用户从一组单选按钮中选择比萨饼类型然后“订购”比萨饼并显示与比萨饼类型匹配的图像。我的问题是除非我重新调整窗口大小，否则不会显示图像。我哪里错了？
这是我的源代码：

package gui;
import javax.swing.*;

import java.awt.*;
import java.awt.event.*;
public class GUI extends JFrame{
    //all my variables
    private JRadioButton pepperoni;
    private JRadioButton cheese;
    private JRadioButton jalepeno;
    private JRadioButton sausage;
    private JRadioButton hawiian;
    private JRadioButton spinach;
    private ButtonGroup group;
    private ImageIcon pizza;
    private JLabel displayed;
    private JButton submit;
    public GUI () {
        super("Order a Pizza");
        setLayout(new FlowLayout());
        //give instructions and assign variables
        JLabel instructions = new JLabel("Choose which Pizza you want to order");
        add(instructions);
        pepperoni = new JRadioButton("Pepperoni Pizza", true);
        cheese = new JRadioButton("Cheese Pizza", false);
        jalepeno = new JRadioButton("Hot Jalepeno Pizza", false);
        sausage = new JRadioButton("Sausage Pizza", false);
        hawiian = new JRadioButton("Hawaii Style - PineApple and sausage", false);
        spinach = new JRadioButton("Spinach Pizza", false);
        submit = new JButton("Order Pizza");
        //add to jframe
        add(pepperoni);
        add(cheese);
        add(jalepeno);
        add(sausage);
        add(hawiian);
        add(submit);
        add(spinach);
        //add to button group
        group = new ButtonGroup();
        group.add(pepperoni);
        group.add(cheese);
        group.add(jalepeno);
        group.add(sausage);
        group.add(hawiian);
        group.add(spinach);
        //add event listeners
        pepperoni.addItemListener(new RadioHandler(new ImageIcon(getClass().getResource("pepperoni.jpg"))));
        cheese.addItemListener(new RadioHandler(new ImageIcon(getClass().getResource("download.jpg"))));
        jalepeno.addItemListener(new RadioHandler(new ImageIcon(getClass().getResource("jalepeno.jpg"))));
        sausage.addItemListener(new RadioHandler(new ImageIcon(getClass().getResource("sausage.jpg"))));
        hawiian.addItemListener(new RadioHandler(new ImageIcon(getClass().getResource("hawiian.png"))));
        submit.addActionListener(new SubmitHandler());
    }
    //class that sets file when radio is clicked
    public class RadioHandler implements ItemListener {

        ImageIcon file;
        //constructor for whatever image should be displayed when clicked
        public RadioHandler (ImageIcon img) {
            file = img;
        }
        //when clicked set that image
        public void itemStateChanged(ItemEvent event) {
            pizza = file;
            displayed = new JLabel(pizza);
        }

    }
    //class that displays image when user submits
    public class SubmitHandler implements ActionListener {

        public void actionPerformed (ActionEvent event) {
            if (event.getSource() instanceof JButton) {//if the button is clicked - i dont think i really need this
                add(displayed);//add image
            }

        }

    }
}

主要方法：

package main;
 import gui.GUI;
public class Main {

    public static void main(String[] args) {
        GUI go = new GUI();
        go.setSize(800, 600);
        go.setVisible(true);
    }

}

Answer 1

正如@nIcEcOw所说..

  

..只使用JLabel.setIcon ( newImage )而不是无缘无故地重新创建JLabel

这是实现该想法的代码版本，但几乎没有其他更改。它仍然需要在评论和其他调整中提到的EDT上创建GUI。

import java.awt.*;
import javax.swing.*;
import javax.swing.border.EmptyBorder;

import javax.swing.*;

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;

public class GUI extends JFrame {

    //all my variables
    private JRadioButton pepperoni;
    private JRadioButton cheese;
    private JRadioButton jalepeno;
    private JRadioButton sausage;
    private JRadioButton hawiian;
    private JRadioButton spinach;
    private ButtonGroup group;
    private ImageIcon pizza;
    private JLabel displayed = new JLabel();
    private JButton submit;

    public GUI() {
        super("Order a Pizza");
        setLayout(new FlowLayout());
        //give instructions and assign variables
        JLabel instructions = new JLabel("Choose which Pizza you want to order");
        add(instructions);
        pepperoni = new JRadioButton("Pepperoni Pizza", true);
        cheese = new JRadioButton("Cheese Pizza", false);
        jalepeno = new JRadioButton("Hot Jalepeno Pizza", false);
        sausage = new JRadioButton("Sausage Pizza", false);
        hawiian = new JRadioButton("Hawaii Style - PineApple and sausage", false);
        spinach = new JRadioButton("Spinach Pizza", false);
        submit = new JButton("Order Pizza");
        //add to jframe
        add(pepperoni);
        add(cheese);
        add(jalepeno);
        add(sausage);
        add(hawiian);
        add(submit);
        add(spinach);
        //add to button group
        group = new ButtonGroup();
        group.add(pepperoni);
        group.add(cheese);
        group.add(jalepeno);
        group.add(sausage);
        group.add(hawiian);
        group.add(spinach);
        //add event listeners
        pepperoni.addItemListener(new RadioHandler(new ImageIcon(getImage(20, 80))));
        cheese.addItemListener(new RadioHandler(new ImageIcon(getImage(20, 40))));
        jalepeno.addItemListener(new RadioHandler(new ImageIcon(getImage(80, 20))));
        sausage.addItemListener(new RadioHandler(new ImageIcon(getImage(80, 60))));
        hawiian.addItemListener(new RadioHandler(new ImageIcon(getImage(80, 40))));
        submit.addActionListener(new SubmitHandler());

        add(displayed);//add image
    }

    private static Image getImage(int w, int h) {
        return new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
    }

    //class that sets file when radio is clicked
    public class RadioHandler implements ItemListener {

        ImageIcon file;

        //constructor for whatever image should be displayed when clicked
        public RadioHandler(ImageIcon img) {
            file = img;
        }

        //when clicked set that image
        public void itemStateChanged(ItemEvent event) {
            pizza = file;

        }
    }

    //class that displays image when user submits
    public class SubmitHandler implements ActionListener {

        public void actionPerformed(ActionEvent event) {
            if (event.getSource() instanceof JButton) {//if the button is clicked - i dont think i really need this
                displayed.setIcon(pizza);
            }
        }
    }

    public static void main(String[] args) {
        GUI go = new GUI();
        go.setSize(800, 600);
        go.setVisible(true);
    }
}