How to make a rectangle in Graphics in a transparent colour?

问题

I'm trying to paint a rectangle on my application in a red shade but I need to make it sort of transparent so that the component under it will still show. However I still want that some colour will still show. The method where I'm drawing is the following:

protected void paintComponent(Graphics g) {
    if (point != null) {
        int value = this.chooseColour(); // used to return how bright the red is needed

        if(value !=0){
            Color myColour = new Color(255, value,value );
            g.setColor(myColour);
            g.fillRect(point.x, point.y, this.width, this.height);
        }
        else{
            Color myColour = new Color(value, 0,0 );
            g.setColor(myColour);
            g.fillRect(point.x, point.y, this.width, this.height);
        }
    }
}

Does anyone know how I can make the red shade a bit transparent? I don't need it completely transparent though.

回答1:

int alpha = 127; // 50% transparent
Color myColour = new Color(255, value, value, alpha);

See the Color constructors that take 4 arguments (int or float) for further details.

回答2:

Try this:

protected void paintComponent(Graphics g) {
    if (point != null) {
        int value = this.chooseColour(); // used to return how bright the red is needed
        g.setComposite(AlphaComposite.SrcOver.derive(0.8f));

        if(value !=0){
            Color myColour = new Color(255, value,value );
            g.setColor(myColour);
            g.fillRect(point.x, point.y, this.width, this.height);
        }
        else{
            Color myColour = new Color(value, 0,0 );
            g.setColor(myColour);
            g.fillRect(point.x, point.y, this.width, this.height);
        }
        g.setComposite(AlphaComposite.SrcOver);

    }
}

来源：https://stackoverflow.com/questions/8110975/how-to-make-a-rectangle-in-graphics-in-a-transparent-colour