ADDITIONAL SYSTEM INFORMATION :
Windows 10
JDK 1.8.0_292, JDK 11.0.11, JDK 15.0.2, JDK 16.0.1
Screen Resolution: 4K (250% & 150%), 2K (100%)

A DESCRIPTION OF THE PROBLEM :
A fade in and out animation of anti aliased text is ugly as the text is rendered incorrectly with alpha composite < 1.0

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run sample

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
No observable difference when rendering anti aliased text with alpha = 1f and alpha = 0.99f
ACTUAL -
When running the sample you see a significant flickering that should not be observable as we only animate between alpha=1 and alpha = 0.99f.

---------- BEGIN SOURCE ----------
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.Timer;
import javax.swing.UIManager;
import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.RenderingHints;

import static java.awt.RenderingHints.KEY_TEXT_ANTIALIASING;
import static java.awt.RenderingHints.KEY_TEXT_LCD_CONTRAST;

public final class AlphaSample {

  private static final String TEXT = "abcdefghiklmnopqrwstuvwxyz ABCDEFGHIKLMNOPQRSTUVWXYZ";

  public static void main(String[] args) {
    JFrame frame = new JFrame("Alpha");
    MyComponent component = new MyComponent();
    frame.getContentPane().add(component);

    frame.setBounds(100, 100, 600, 400);
    frame.setVisible(true);
    Timer timer = new Timer(100, event -> {
      if (component.alpha == 1f) {
        component.alpha = 0.99f;
      }
      else {
        component.alpha = 1f;
      }
      component.repaint();
    });
    timer.setRepeats(true);
    timer.start();
  }

  private static final class MyComponent extends JComponent {

    private float alpha = 1f;
    private int y;

    @Override
    protected void paintComponent(Graphics g) {
      Graphics2D g2 = (Graphics2D) g;

      Rectangle clip = g2.getClipBounds();
      g2.setColor(Color.WHITE);
      g2.fillRect(clip.x, clip.y, clip.width, clip.height);

      y = 0;
      draw(g2, new Font(Font.DIALOG, Font.PLAIN, 10));
      draw(g2, new Font("Segoe UI", Font.PLAIN, 10));

      draw(g2, new Font(Font.DIALOG, Font.PLAIN, 20));
      draw(g2, new Font("Segoe UI", Font.PLAIN, 20));
    }

    private void draw(Graphics2D g2, Font font) {
      drawString(g2, font, 1f, false);
      drawString(g2, font, 0.99f, false);
      drawString(g2, font, alpha, false);

      y += 10;
      drawString(g2, font, 1f, true);
      drawString(g2, font, 0.99f, true);
      drawString(g2, font, alpha, true);

      y += 20;
    }

    private void drawString(Graphics2D g2, Font font, float alpha, boolean antiAlias) {
      g2.setColor(Color.BLACK);
      g2.setFont(font);
      y += g2.getFontMetrics().getHeight();
      if (antiAlias) {
        g2.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING, RenderingHints.VALUE_TEXT_ANTIALIAS_LCD_HRGB);
      }
      else {
        g2.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING, RenderingHints.VALUE_TEXT_ANTIALIAS_OFF);
      }
      AlphaComposite alphaComposite = AlphaComposite.getInstance(AlphaComposite.SRC_OVER, alpha);
      g2.setComposite(alphaComposite);
      g2.drawString(TEXT + ", font=" + font.getName() + " " + font.getSize() + ", antiAlias=" + antiAlias + ", alpha=" + alpha, 10, y);
    }
  }
}

---------- END SOURCE ----------

FREQUENCY : always