Question

Shape类有一个抽象的绘制，它带有一个Graphics对象...例如，如果我想绘制一个矩形，在我写的情况下为2：

shapetype.draw(g); // he said that g is undefined

我应该如何初始化g以调用函数draw（g）：

    public class main extends Applet 
    {
        Shape shapetype; // shapeClass has 3 subclasses

        public void init() 
        {
            super.init();

// ask user to choose the type of shape 1-line 2-rectangle 3-oval
// int choice =  the type of shape         
            switch(choice)
            {

                case 1:
                // draw line
                    break;

                // draw Rectangle
                case 2:
                //ask user for x,y,width and height
                shapetype = new Rectangle(x1,y1,w,h);
                shapetype.draw(g); // to draw a rectangle
                    break;

                case 3:
              // draw Oval
                    break;

                default:
                    break;
            }
        }

        public void paint(Graphics g) 
        {super.paint(g); }

    }

Answer 1

将绘制调用移至paint方法：

@Overrride // since you're overriding.
public void paint(Graphics g) {
    super.paint(g);

    if(shapetype != null) {
        shapetype.draw(g);
    }
}

仅绘制一次形状是不够的，每次调用paint时都会被覆盖，因此需要重新绘制。

调用一个以Graphics g作为参数的方法

1 个答案: