java에서 GridBagLayout으로 화면 분할이 안됩니다.

import java.awt.*;
 
class GridBag extends Frame {
  private Label[] lb=new Label[4];
  private GridBagLayout gb;
  private GridBagConstraints gbcon;
  public GridBag() {
    lb[0]=new Label("label1");
    lb[1]=new Label("label2");
    lb[2]=new Label("label3");
    lb[3]=new Label("label4");
    lb[0].setBackground(Color.RED);
    lb[1].setBackground(Color.GREEN);
    lb[2].setBackground(Color.BLUE);
    lb[3].setBackground(Color.CYAN);
    gb=new GridBagLayout();
    setLayout(gb);
    gbcon=new GridBagConstraints();
    gbcon.fill=GridBagConstraints.BOTH;
    gbcon.weightx=1.0;
    gbcon.weighty=1.0;
 
    makeCell(0,0,1,1,lb[0]);
    makeCell(1,0,2,1,lb[1]);
    makeCell(0,1,2,1,lb[2]);
    makeCell(2,1,1,1,lb[3]);
    setBounds(300,300,400,200);
    setVisible(true);
    }
  public void makeCell(int x, int y, int width, int height, Label l) {
    gbcon.gridx=x;
    gbcon.gridy=y;
    gbcon.gridwidth=width;
    gbcon.gridheight=height;
    gb.setConstraints(l,gbcon);
    add(l);
    }
}
 
public class ExecuteGridBag {
  public static void main(String[] args) {
    GridBag mygridbag=new GridBag();
    }
}