如何在一个窗口中制作两种颜色？

Question

I want to do the same like this:

Here's the code:

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

class QuizGUI {
    public static void main(String args[]) {
        JFrame frm = new JFrame("Simple Quiz");
        frm.setLayout(null);
        JLabel lbl1 = new JLabel("Which Animal can fly?");
        JLabel lbl2 = new JLabel("You have selected: ");
        JLabel lblOutput = new JLabel();
        JRadioButton rCat = new JRadioButton("Cat");
        JRadioButton rBird = new JRadioButton("Bird");
        JRadioButton rFish = new JRadioButton("Fish");
        ButtonGroup bg = new ButtonGroup();

        bg.add(rCat);
        bg.add(rBird);
        bg.add(rFish);

        lbl1.setBounds(0, 0, 200, 20);
        rCat.setBounds(0, 20, 100, 20);
        rBird.setBounds(0, 40, 100, 20);
        rFish.setBounds(0, 60, 100, 20);
        lbl2.setBounds(0, 80, 200, 20);
        lblOutput.setBounds(0, 105, 200, 20);

        frm.add(lbl1);
        frm.add(rCat);
        frm.add(rBird);
        frm.add(rFish);
        frm.add(lbl2);
        frm.add(lblOutput);

        rCat.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                if (rCat.isSelected()) {
                    lblOutput.setText("Cat can't fly, Try again.");
                }
            }
        });

        rBird.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                if (rBird.isSelected()) {
                    lblOutput.setText("Bird can fly, Excellent.");
                }
            }
        });

        rFish.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                if (rFish.isSelected()) {
                    lblOutput.setText("Cat can't fly, Try again.");
                }
            }
        });

        frm.setVisible(true);
        frm.setSize(350, 200);

        frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}

The problem is, I want the colors of window like image the background is white and the background for choices is gray.

I tried frame.setBackground but doesn't work.

I tried some codes for another examples and the color was white. I don't know why the window is all gray like this:

Answer 1

From the code you posted in your question:

frm.setLayout(null);

This is not a good idea. I recommend always using a layout manager . JFrame is a top-level container . It has a content pane which, by default, is a JPanel . The default layout manager for the content pane is BorderLayout . You can refer to the source code for JFrame in order to confirm this.

In my opinion BorderLayout is suitable for your GUI. One JPanel is the NORTH component and it displays the question, namely Which Animal can fly? , the radio buttons are the CENTER component and the text You have selected: is the SOUTH panel.

Each JPanel can then have its own background color. I am using JDK 13 on Windows 10 and the default background color is gray. Hence, in the code below, I set the background color for the NORTH and SOUTH panels and leave the CENTER panel with its default background color.

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.FlowLayout;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.ButtonGroup;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.WindowConstants;

public class QuizGUI implements ActionListener, Runnable {
    private static final String BIRD = "Bird";
    private static final String CAT = "Cat";
    private static final String FISH = "Fish";

    private JFrame frame;
    private JLabel resultLabel;

    @Override // java.awt.event.ActionListener
    public void actionPerformed(ActionEvent event) {
        String actionCommand = event.getActionCommand();
        switch (actionCommand) {
            case BIRD:
                resultLabel.setText(BIRD + " can fly. Excellent.");
                break;
            case CAT:
                resultLabel.setText(CAT + " can't fly. Try again.");
                break;
            case FISH:
                resultLabel.setText(FISH + " can't fly. Try again.");
                break;
            default:
                resultLabel.setText(actionCommand + " is not handled.");
        }
    }

    @Override // java.lang.Runnable
    public void run() {
        createAndShowGui();
    }

    private void createAndShowGui() {
        frame = new JFrame("Simple Quiz");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.add(createQuestionPanel(), BorderLayout.PAGE_START);
        frame.add(createChoicesPanel(), BorderLayout.CENTER);
        frame.add(createOutcomePanel(), BorderLayout.PAGE_END);
        frame.setSize(350, 200);
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    private void createRadioButton(String text, ButtonGroup bg, JPanel panel) {
        JRadioButton radioButton = new JRadioButton(text);
        radioButton.addActionListener(this);
        bg.add(radioButton);
        panel.add(radioButton);
    }

    private JPanel createChoicesPanel() {
        JPanel choicesPanel = new JPanel(new GridLayout(0, 1));
        ButtonGroup bg = new ButtonGroup();
        createRadioButton(CAT, bg, choicesPanel);
        createRadioButton(BIRD, bg, choicesPanel);
        createRadioButton(FISH, bg, choicesPanel);
        return choicesPanel;
    }

    private JPanel createOutcomePanel() {
        JPanel outcomePanel = new JPanel(new GridLayout(0, 1, 0, 5));
        outcomePanel.setBackground(Color.WHITE);
        JLabel promptLabel = new JLabel("You have selected:");
        setBoldFont(promptLabel);
        outcomePanel.add(promptLabel);
        resultLabel = new JLabel("    ");
        outcomePanel.add(resultLabel);
        return outcomePanel;
    }

    private JPanel createQuestionPanel() {
        JPanel questionPanel = new JPanel(new FlowLayout(FlowLayout.LEADING));
        questionPanel.setBackground(Color.WHITE);
        JLabel questionLabel = new JLabel("Which Animal can fly?");
        setBoldFont(questionLabel);
        questionPanel.add(questionLabel);
        return questionPanel;
    }

    private void setBoldFont(JLabel label) {
        Font boldFont = label.getFont().deriveFont(Font.BOLD);
        label.setFont(boldFont);
    }

    public static void main(String[] args) {
        String slaf = UIManager.getSystemLookAndFeelClassName();
        try {
            UIManager.setLookAndFeel(slaf);
        }
        catch (ClassNotFoundException |
               IllegalAccessException |
               InstantiationException |
               UnsupportedLookAndFeelException x) {
            System.out.println("WARNING (ignored): Failed to set [system] look-and-feel");
            x.printStackTrace();
        }
        EventQueue.invokeLater(new QuizGUI());
    }
}

Answer 2

First create a private JPanel called contentPane in your QuizGUI class. Then in your main method, type:

contentPane = new JPanel();
contentPane.setBackground(Color.WHITE);
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
frm.setContentPane(contentPane);
contentPane.setLayout(null);

then, change all frm.add() with contentPane.add()

I hope this helped!