如何从我的主 class 向我的 canvas 绘制一个矩形？

Question

我知道我可以用缓冲策略（在循环内）做到这一点，但是有没有办法在没有缓冲策略（在循环内）的情况下做到这一点？

import javax.swing.JFrame;

public class JavaApplication28 {

    public static void main(String[] args) {
        JFrame f = new JFrame("Title");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        MyCanvas mycanvas = new MyCanvas();
        f.add(mycanvas);
        f.setSize(400,250);
        f.setVisible(true); 

        //I would like to create the rectangle on the canvas here, which is possible with bufferstrategy

    }
}

import java.awt.Canvas;
import java.awt.Graphics;

public class MyCanvas extends Canvas{
    public MyCanvas (){
        
    }

    //Do I call paint() in my main class, something like mycanvas.paint().drawRect(100, 100, 100, 100)? Is there such syntax?
 
    public void paint(Graphics g) {
        super.paint(g);
        g.drawRect(100, 100, 100, 100);
    }
}

Answer 1

我不记得 AWT canvases 是否有 repaint()... 20 年没用过:) 在 canvas 和 add/remove 中保存“渲染”对象的集合，并根据需要重新绘制。

public class MyCanvas extends Canvas{
    private final List<Shape> shapes;
    public MyCanvas (){
        shapes = new ArrayList();
    }

    public List<Shape> renderedShapes() {
       return shapes;
    }
    
    public void paint(Graphics g) {
        super.paint(g);
        // the shapes are created in the main class but once you add them to the renderedShapes() array of this canvas, you have access to them and the graphics context at this point and can render them.
        for (Shape s : shapes) {               
           renderShape(g, s);
        }
    }
}

private void renderShape(Graphics g, Shape shape) {
   if (Shape instanceof Rectangle) {
          Rectangle rect = (Rectangle)shape;
          g.drawRect(rect.x, rect.y, rect.width, rect.height);
   } else if (Shape instanceof Circle) {
       Circle circle = (Circle)shape;
       g.drawCircle(circle.x, circle.y, circle.radius);
   }

}

public static void main(String[] args) {
   MyCanvas canvas = new MyCanvas();
   canvas.renderedShapes().add(new Rectangle(0,0,10,10));
   canvas.repaint();

}

如何从我的主 class 向我的 canvas 绘制一个矩形？

How can I draw a rectangle to my canvas from my main class?

java

canvas

awt