如何在JFrame框中显示用户输入？

Question

I have written this code that asks user which shape you want to display and then show it in the JFrame box, my problem is the question is shown in the console box (inside eclipse) not in the JFrame box, so how can I change that?

Also the question is repeated twice am not sure why.

 public void paintComponent(Graphics g) {
     super.paintComponent(g);
     this.setBackground(Color.WHITE);


     Scanner user_input = new Scanner(System.in);
    int shape_num;
    System.out.println("What is the shape you want to draw? 1- Rectangle 2- Circle");
    shape_num = user_input.nextInt();
     if(shape_num ==1){  
     g.setColor(Color.BLUE);
     g.fillRect(25, 25, 150, 50);
     }
     else if(shape_num ==2) {
     g.setColor(Color.RED);
     g.fillOval(25, 80, 100, 100);
 }
     else if (shape_num  > 2) {
         System.out.println("Error");
     }
 }
     public static void main(String[] args){

            JFrame f = new JFrame("Title");
            f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            Rectangle r = new Rectangle();
            f.add(r);
            f.setSize(400, 250);
            f.setVisible(true);


        }

}

Answer 1

Holy mother of all things precious, don't use a Scanner that uses System.in in the middle of a paintComponent method. This will grind your GUI program to a screeching halt. Seriously. This method is one of the most important determinants of the perceived responsiveness of your GUI program, and if you slow it down in any way, or stop it (as you're doing), your program will completely freeze. If you're coding a GUI, then do all user interaction through the GUI, not through the console.

For instance, you could use JRadioButtons that change the state of a field in the GUI, and then draw the image accordingly. For example:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;

public class ItssRectangle extends JPanel {
    private static final String RECTANGLE = "Rectangle";
    private static final String OVAL = "Oval";
    private static final String[] SHAPES = { RECTANGLE, OVAL };
    private static final int PREF_W = 400;
    private static final int PREF_H = 250;
    private String shapeText = "";
    private ButtonGroup buttonGroup = new ButtonGroup();

    public ItssRectangle() {
        RadioBtnListener radioBtnListener = new RadioBtnListener();
        JPanel panel = new JPanel();
        for (String shape : SHAPES) {
            JRadioButton rBtn = new JRadioButton(shape);
            rBtn.setOpaque(false);
            rBtn.setActionCommand(shape);
            rBtn.addActionListener(radioBtnListener);
            panel.add(rBtn);
            buttonGroup.add(rBtn);
        }

        panel.setOpaque(false);
        setLayout(new BorderLayout());
        add(panel, BorderLayout.PAGE_START);

    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        if (RECTANGLE.equals(shapeText)) {
            g.setColor(Color.BLUE);
            g.fillRect(25, 25, 150, 50); // TODO: Get rid of magic numbers
        } else if (OVAL.equals(shapeText)) {
            g.setColor(Color.RED);
            g.fillOval(25, 80, 100, 100); // TODO: Ditto!
        }
    }

    @Override
    public Dimension getPreferredSize() {
        if (isPreferredSizeSet()) {
            return super.getPreferredSize();
        }
        return new Dimension(PREF_W, PREF_H);
    }

    private class RadioBtnListener implements ActionListener {
        @Override
        public void actionPerformed(ActionEvent e) {
            shapeText = e.getActionCommand();
            repaint();
        }
    }

    private static void createAndShowGui() {
        ItssRectangle mainPanel = new ItssRectangle();

        JFrame frame = new JFrame("ItssRectangle");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGui();
            }
        });
    }
}

Note that in the code above, the paintComponent method is for painting and painting only . No user interaction, even of a GUI kind, goes on in there -- just painting.