com.sun.java.swing.plaf.gtk.GTKLookAndFeel has unnecessary casts to GTKStyleFactory

ADDITIONAL SYSTEM INFORMATION :
JDK 1.8.0.202

A DESCRIPTION OF THE PROBLEM :
In com.sun.java.swing.plaf.gtk.GTKLookAndFeel there are unneccessary casts of javax.swing.plaf.synth.SynthStyleFactory to com.sun.java.swing.plaf.gtk.GTKStyleFactory, for example in the inner class FontLazyValue.

This breaks applications, which change the style factory. For example, IntelliJ uses the following UI tweak:

            if (!UIUtil.isUnderGTKLookAndFeel()) return;

            final SynthStyleFactory original = SynthLookAndFeel.getStyleFactory();

            SynthLookAndFeel.setStyleFactory(new SynthStyleFactory() {
              @Override
              public SynthStyle getStyle(final JComponent c, final Region id) {
                final SynthStyle style = original.getStyle(c, id);
                if (id == Region.POPUP_MENU) {
                  final Integer x = ReflectionUtil.getField(style.getClass(), style, int.class, "xThickness");
                  if (x != null && x == 0) {
                    ReflectionUtil.setField(style.getClass(), style, int.class, "xThickness", 1);
                    ReflectionUtil.setField(style.getClass(), style, int.class, "yThickness", 3);
                  }
                }
                return style;
              }
            });
        
            new JPopupMenu(); // invokes updateUI() -> updateStyle()
        
            SynthLookAndFeel.setStyleFactory(original);

Because the only called method #getStyle is present in the base class SynthStyleFactory, the cast to GTKStyleFactory is unneccessary.

Instead of

            public Object createValue(UIDefaults table) {
                GTKStyleFactory factory = (GTKStyleFactory)getStyleFactory();
                GTKStyle style = (GTKStyle)factory.getStyle(null, region);
                return style.getDefaultFont();
            }


you can simply write:

            public Object createValue(UIDefaults table) {
                SynthStyleFactory factory = getStyleFactory();
                GTKStyle style = (GTKStyle)factory.getStyle(null, region);
                return style.getDefaultFont();
            }

REGRESSION : Last worked in version 8u202

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
see above

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
see above

---------- BEGIN SOURCE ----------
see above
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FREQUENCY : always