我的构造函数是否导致我的JFrame显示空白？

Question

我试图在JFrame中绘制随机大小的正方形，但JFrame变成空白。

我正在尝试恢复旧代码，并在进行了一些挖掘之后，在这里，我认为问题可能出在我的构造函数中？我知道代码可以在某一时刻起作用，并希望有人可以将我指向正确的方向

变量：

int sizeBig = 150;
int canvasW = 1300;
int canvasH = 750;
Random rand = new Random();
int initialS = 1;
int numberS = 40;
int smallsizeVAR = sizeBig / 3;
int border1=0;

    /* Black  */    
String color1 = "#000000";
String color2 = "#000000";
String color3 = "#000000";
String color4 = "#000000";
String color5 = "#000000";
String color6 = "#000000";
String color7 = "#000000";
String color8 = "#000000";
String colorBG= "#ffffff";

我绘制正方形的代码：

                    public void paint(final Graphics g) {
                    g.setColor(Color.decode(colorBG));
                    g.fillRect(0, 0, canvasW, canvasH);

                    // while

                    while (initialS <= numberS) {
                        final int randX = rand.nextInt(canvasW + sizeBig) + (0 - sizeBig);
                        final int randY = rand.nextInt(canvasH + sizeBig) + (0 - sizeBig);

                        // size random

                        final int sizeRAND = rand.nextInt(((sizeBig + 1) - smallsizeVAR) + 1) + smallsizeVAR;

                        // end size rnd

                        // rand color 1-4
                        final String[] arr = { color2, color3, color4, color5, color6, color7, color8 };
                        final Random random = new Random();
                        final int select = random.nextInt(arr.length);

                        g.setColor(Color.decode(arr[select]));
                        g.fillRect(randX, randY, sizeRAND, sizeRAND);
                        g.setColor(Color.decode(colorBG));
                        g.fillRect(randX + (sizeRAND - ((4 * sizeRAND) / 5)) / 2, randY + (sizeRAND - ((4 * sizeRAND) / 5)) / 2,
                                ((4 * sizeRAND) / 5), (4 * sizeRAND) / 5);
                        initialS++;

                        if (initialS == numberS) {
                            g.setColor(Color.decode(arr[select]));
                            g.fillRect(canvasW / 8, canvasW / 8, (3 * sizeBig) / 2, (3 * sizeBig) / 2); 


                        }
                    }
                    // end while
                }

我的构造函数：

                    // The constructor follows:
                public GraphicsDemo_noborders() {
                    setTitle("Programatic Art");
                    setSize(canvasW, canvasH);
                    setVisible(true);
                    setDefaultCloseOperation(EXIT_ON_CLOSE);
                }

主要：

                public static void main(String args[]) {

                    GraphicsDemo_noborders demo = new GraphicsDemo_noborders();

                }