Caixa de Texto

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.GridLayout;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class Estudos extends JFrame {  
    public Estudos() {  
        super("Calc");  
        Container tela = getContentPane();  
        BorderLayout layout = new BorderLayout();  
        GridLayout numeros = new GridLayout(4, 3);  
        GridLayout operacoes = new GridLayout(4, 1);  
        JPanel painelCentro = new JPanel(numeros);  
        JPanel painelOperacoes = new JPanel(operacoes);  
        
        JTextField textField = new JTextField();
          
        tela.setLayout(layout);  
        tela.add(painelCentro, layout.CENTER);  
        tela.add(painelOperacoes, layout.EAST);  
        JButton bt2 = new JButton("NORTH");  
        JButton btenter = new JButton("ENTER");  
          
        JButton control7 = new JButton("7");  
        JButton control8 = new JButton("8");  
        JButton control9 = new JButton("9");  
        JButton control4 = new JButton("4");  
        JButton control5 = new JButton("5");  
        JButton control6 = new JButton("6");  
        JButton control1 = new JButton("1");  
        JButton control2 = new JButton("2");  
        JButton control3 = new JButton("3");  
        JButton control0 = new JButton("0");  
        JButton controlp = new JButton(".");  
        JButton controlv = new JButton(",");  
          
        JButton controldiv = new JButton("/");  
        JButton controlmul = new JButton("*");  
        JButton controlsub = new JButton("-");  
        JButton controlsom = new JButton("+");  
       
        painelCentro.add(control7);  
        painelCentro.add(control8);  
        painelCentro.add(control9);  
        painelCentro.add(control4);  
        painelCentro.add(control5);  
        painelCentro.add(control6);  
        painelCentro.add(control1);  
        painelCentro.add(control2);  
        painelCentro.add(control3);  
        painelCentro.add(control0);  
        painelCentro.add(controlp);  
        painelCentro.add(controlv);  
          
        painelOperacoes.add(controldiv);  
        painelOperacoes.add(controlmul);  
        painelOperacoes.add(controlsub);  
        painelOperacoes.add(controlsom);  
          
        JPanel panelSuperior = new JPanel(new GridLayout(2, 1));
        panelSuperior.add(bt2);
        panelSuperior.add(textField);
        
        tela.add(BorderLayout.NORTH, panelSuperior);  
        tela.add(BorderLayout.SOUTH, btenter);  
  
        setSize(200, 200);  
        setVisible(true);  
    }  
  
    public static void main(String[] args) {  
        Estudos app = new Estudos();  
        app.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
    }  
}