2048 Game Implementation In Java - Rectangle In GameBox

I want to implement the 2048 game in Java.

I made the game logics, but now I need to implement the interface.

I made 2 classes GameBox and ContainerBox that extends JComponent.

I painted in GameBox a rectangle and now I want to initialize a matrics of GameBoxes in ContainerBox so I used:

GameBox GB[][] = new GameBox[4][4];

I am thinking about drawing the Boxes in something like this:

for(int i=0;i<4;i++)

for(int j=0;j<4;j++)

but I don't know how to draw those rectangles in the for...