Name: dsC58869 Date: 03/27/2000


The method java.awt.Component.isOpaque() works wrong
for undisplayable component. In this case it returns true,
but should return false by documentation:
    /**
     * Returns true if this component is completely opaque, returns
     * false by default.
       ^^^^^^^^^^^^^^^^
     * <p>
     * An opaque component paints every pixel within its
     * rectangular region. A non-opaque component paints only some of
     * its pixels, allowing the pixels underneath it to "show through".
     * A component that does not fully paint its pixels therefore
     * provides a degree of transparency. Only lightweight
     * components can be transparent.
     * <p>
     * Subclasses that guarantee to always completely paint their
     * contents should override this method and return true. All
     * of the "heavyweight" AWT components are opaque.
     *
     * @return true if this component is completely opaque.
     * @see #isLightweight
     * @since 1.2
     */

Here is a minimized test:
import java.awt.*;

public class ComponentTest2 {
    public static void main (String[] args) {
        Component c = new StubComponent();
        Frame fr = new Frame();
        System.out.println("Undisplayable Component:");
        if (c.isOpaque()) {
            System.out.println("FAILED: Componenet is opaque by default");
        } else {
            System.out.println("OKAY");
        }
        fr.add(c);
        fr.pack();
        while (! fr.isDisplayable()) {
            Thread.yield();
        }
        System.out.println("Displayable Component:");
        if (c.isOpaque()) {
            System.out.println("FAILED: Componenet is opaque by default");
        } else {
            System.out.println("OKAY");
        }
        System.exit(0);
    }
}
class StubComponent extends Component {
    public StubComponent() {
        super();
    }
}

Output:
%java -version
java version "1.3.0rc2"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.0rc2-Y)
Java HotSpot(TM) Client VM (build 1.3.0rc2-Y, interpreted mode)
%java ComponentTest2
Undisplayable Component:
FAILED: Componenet is opaque by default
Warning:
    Cannot allocate colormap entry for default background
Displayable Component:
OKAY

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