Java图形-无法正确绘制

Question

Learning to use graphics in java and currently at the moment i'm trying to add some graphics to the screen but failing. I've tried different approaches in a trial and error fashion yet had no luck. The code shown, the structure cannot change in terms of having paint method in a separate class for example. Its a simplified version on a project I'm working on.

Other questions on stackoverflow have helped to an extend and similar with the oracle website but I'm still facing issues hence why I am asking here.

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

public class test
{
    public static void main(String Args[])
    {
    panelme p1 = new panelme();
    }

}

class panelme
{
    JFrame mainPanel;

    panelme ()
    {
    mainPanel = new JFrame();
    mainPanel.setSize(1000,1000);
    mainPanel.setDefaultCloseOperation(mainPanel.EXIT_ON_CLOSE);
    //paintFrame();
    //paintFrame(g);
    //paintFrame(null);
    mainPanel.setVisible(true);
    }

    public void paintFrame(Graphics g)
    {
    g.drawString("This is a string!", 30, 40);
    //repaint();
    }
}

Answer 1

Start by taking a look at Painting in AWT and Swing and Performing Custom Painting for more details about how painting works in Swing

Next, take a look at 2D Graphics trail

Next, create your self a custom class which extends from JPanel and then override it's paintComponent method and place your custom painting within it...

public class PaintPane extends JPanel {
    @Override
    public Dimension getPreferredSize() {
        return new Dimension(200, 200);
    }

    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawString("This is a string!", 30, 40);
    }
}

Next, add your custom panel to a window...

EventQueue.invokeLater(new Runnable() {
    @Override
    public void run() {
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
            ex.printStackTrace();
        }

        JFrame frame = new JFrame("Testing");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(new PaintPane());
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
});