java - How can i add two class that extends JPanel in One JFrame -

i created 2 class extends jpanel , want add 2 class in 1 frame. unable it. please.

my classes -->

import java.awt.gridlayout;  import javax.swing.jbutton; import javax.swing.jframe; import javax.swing.jpanel;  public class calbutton extends jpanel {     private jbutton[] buttons;     private static final string[] buttonnames = { "7", "8", "9", "/", "4", "5",             "6", "*", "1", "2", "3", "-", "0", ".", "=", "+" };     private jpanel buttonpanel;      public calbutton() {         // todo auto-generated constructor stub         buttons = new jbutton[buttonnames.length];         buttonpanel = new jpanel();         buttonpanel.setlayout(new gridlayout(4, 4, 3, 3));          for(int i=0; i<buttonnames.length; i++){             buttons[i] = new jbutton(buttonnames[i]);             buttonpanel.add(buttons[i]);          }     } } 

another class-->

import java.awt.gridlayout;  import javax.swing.jpanel; import javax.swing.jtextfield;  public class calfield extends jpanel {     private jpanel panelfield;     private jtextfield field;      public calfield() {         // todo auto-generated constructor stub         panelfield = new jpanel();         panelfield.setlayout(new gridlayout(1, 1,5,5));         field = new jtextfield(20);         panelfield.add(field);      } } 

main class-->

public class calculator {     public static void main(string[] args) {          jframe application = new jframe("calculator");         calfield calfield = new calfield();         calbutton calbutton = new calbutton();         application.setlayout(new gridlayout(2, 1));          application.setdefaultcloseoperation(jframe.exit_on_close);         application.setsize(400, 450);         application.setvisible(true);     } } 

anyone kindly solve problem please. i'm stuck problem.

public calbutton() {     // todo auto-generated constructor stub     buttons = new jbutton[buttonnames.length];     buttonpanel = new jpanel();     buttonpanel.setlayout(new gridlayout(4, 4, 3, 3));      for(int i=0; i<buttonnames.length; i++){         buttons[i] = new jbutton(buttonnames[i]);         buttonpanel.add(buttons[i]);      } } 

the calbutton class "is a" jpanel because extend jpanel there no need create jpanel. add buttons class:

public calbutton() {     // todo auto-generated constructor stub     buttons = new jbutton[buttonnames.length];     //buttonpanel = new jpanel();     //buttonpanel.setlayout(new gridlayout(4, 4, 3, 3));     setlayout(new gridlayout(4, 4, 3, 3));      for(int i=0; i<buttonnames.length; i++){         buttons[i] = new jbutton(buttonnames[i]);         //buttonpanel.add(buttons[i]);         add(buttons[i]);     } } 

same calcfield class except in case don't need set layout manager. can use default flowlayout.

then second problem never add these panels frame:

    calfield calfield = new calfield();     calbutton calbutton = new calbutton();     //application.setlayout(new gridlayout(2, 1));     application.add(calfield, borderlayout.page_start);     application.add(calbutton, borderlayout.center);