有很多（真的很酷）渲染提示！我建议您开始尝试所有这些，然后看看哪种组合可以为您带来预期的效果！

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200,200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            // Remember,graphics is a shared context,when you make changes
            // to it,you should also undo them.  To this end,we use create/dispose
            // which takes a snapshot of the current state and restores it at the
            // end.
            Graphics2D g2 = (Graphics2D) g.create();
            g2.setRenderingHint(RenderingHints.KEY_ALPHA_INTERPOLATION,RenderingHints.VALUE_ALPHA_INTERPOLATION_QUALITY);
            g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);
            g2.setRenderingHint(RenderingHints.KEY_COLOR_RENDERING,RenderingHints.VALUE_COLOR_RENDER_QUALITY);
            g2.setRenderingHint(RenderingHints.KEY_DITHERING,RenderingHints.VALUE_DITHER_ENABLE);
            g2.setRenderingHint(RenderingHints.KEY_FRACTIONALMETRICS,RenderingHints.VALUE_FRACTIONALMETRICS_ON);
            g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION,RenderingHints.VALUE_INTERPOLATION_BILINEAR);
            g2.setRenderingHint(RenderingHints.KEY_RENDERING,RenderingHints.VALUE_RENDER_QUALITY);
            g2.setRenderingHint(RenderingHints.KEY_STROKE_CONTROL,RenderingHints.VALUE_STROKE_PURE);

            g2.setColor(Color.BLACK);
            g2.drawLine(0,getWidth(),getHeight());
            g2.drawLine(getWidth(),getHeight());

            g2.dispose();
        }

    }

}

警告

g2 = (Graphics2D)getGraphics();是一个非常非常糟糕的主意，而不是自定义绘画的工作原理。

getGraphics只不过是上一次绘画过程中最后一次绘画的快照，并且在下一次绘画过程中将无效。

我强烈建议您通读Performing Custom Painting和Painting in AWT and Swing，以更好地了解Swing中的绘画工作原理以及您应该如何使用它。

用鼠标绘图不是一个常见的问题，并且有许多答案。我建议您看看其他一些问题/答案，以了解如何做到这一点并根据您的需要采用它们