about layouts in simple calculator

hi there i am trying to make a calculator with coding sizes,layouts etc. by myself (trying to not use NetBeans and it is not a homework). but i am facing with a problem about empty spaces. i have a TextArea and Buttons but as you can see below i cant handle this space problem. here is my code,

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.GridLayout;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSeparator;
import javax.swing.JTextArea;

public class calculator extends JFrame {

    public calculator(){

        initComponents();

    }

    private void initComponents(){

        JPanel panelScreen = new JPanel(new GridLayout(0,1));

        JTextArea screen = new JTextArea();
        panelScreen.add(screen);

        JFrame frame = new JFrame("CALCULATOR");
        frame.setDefaultCloseOperation(EXIT_ON_CLOSE);

        JPanel panelButtons = new JPanel(new GridLayout(3,3));

        JButton oneButton = new JButton("1");
        panelButtons.add(oneButton);

        JButton twoButton = new JButton("2");
        panelButtons.add(twoButton);

        JButton threeButton = new JButton("3");
        panelButtons.add(threeButton);

        JButton fourButton = new JButton("4");
        panelButtons.add(fourButton);

        JButton fiveButton = new JButton("5");
        panelButtons.add(fiveButton);

        JButton sixButton = new JButton("6");
        panelButtons.add(sixButton);

        JButton sevenButton = new JButton("7");
        panelButtons.add(sevenButton);

        JButton eightButton = new JButton("8");
        panelButtons.add(eightButton);

        JButton nineButton = new JButton("9");
        panelButtons.add(nineButton);

        frame.getContentPane().add(panelScreen, BorderLayout.NORTH);
        //frame.getContentPane().add(new JSeparator(), BorderLayout.CENTER);
        frame.getContentPane().add(panelButtons, BorderLayout.SOUTH);
        frame.setBounds(50, 50, 500, 500);
        frame.setResizable(false);
        //frame.pack();
        frame.setVisible(true);


    }


    public static void main(String[] args) {

        new calculator();

    }

}

and this the picture of programme;

i appreciate if you can help me. anyway thanks :)

Andrew Thompson

import java.awt.*;

import javax.swing.*;
import javax.swing.border.EmptyBorder;

// no need to extend frame!
//public class Calculator extends JFrame {
public class Calculator {

    public Calculator(){    
        initComponents();    
    }

    private void initComponents(){
        // I find it easier to create a panel and SET it as the content pane
        JPanel gui = new JPanel(new BorderLayout(5,5));
        // add some padding to the main GUI
        gui.setBorder(new EmptyBorder(4,4,4,4));

        // not needed if only a single compoinent is to be added!
        //JPanel panelScreen = new JPanel(new GridLayout(0,1));

        // add some constraints to make the output field bigger.
        // if it is intended to be single line, a JTextField should be used.
        JTextArea screen = new JTextArea(2,25);
        gui.add(screen, BorderLayout.NORTH);
        //panelScreen.add(screen);

        JFrame frame = new JFrame("CALCULATOR");
        frame.setContentPane(gui);

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // add padding around the buttons
        JPanel panelButtons = new JPanel(new GridLayout(3,3,4,4));

        JButton oneButton = new JButton("1");
        panelButtons.add(oneButton);

        JButton twoButton = new JButton("2");
        panelButtons.add(twoButton);

        JButton threeButton = new JButton("3");
        panelButtons.add(threeButton);

        JButton fourButton = new JButton("4");
        panelButtons.add(fourButton);

        JButton fiveButton = new JButton("5");
        panelButtons.add(fiveButton);

        JButton sixButton = new JButton("6");
        panelButtons.add(sixButton);

        JButton sevenButton = new JButton("7");
        panelButtons.add(sevenButton);

        JButton eightButton = new JButton("8");
        panelButtons.add(eightButton);

        JButton nineButton = new JButton("9");
        panelButtons.add(nineButton);

        //frame.getContentPane().add(new JSeparator(), BorderLayout.CENTER);

        // Add the buttons to the CENTER and they will
        // fill whatever space they are provided.
        gui.add(panelButtons, BorderLayout.CENTER);
        //frame.setBounds(50, 50, 500, 500);
        //frame.setResizable(false);
        frame.pack();
        frame.setVisible(true); 
    }    

    public static void main(String[] args) {    
       java.awt.EventQueue.invokeLater(new Runnable() {

         @Override
         public void run() {
            new Calculator();
         }
       });    
    }    
}

Hovercraft Full Of Eels

A few suggestions:

Don't set the JFrame's size, and in fact don't set any sizes.
Call pack to all the components to set their own sizes.
If you want the buttons bigger, consider changing the size of their fonts.

e.g.,

import java.awt.BorderLayout;
import java.awt.Font;
import java.awt.GridLayout;

import javax.swing.*;

public class Calc2 {
   public static final String[][] BUTTON_TEXTS = {
      {"7", "8", "9", "+"},
      {"4", "5", "6", "-"},
      {"1", "2", "3", "*"},
      {"0", ".", "/", "="}
   };
   public static final Font BTN_FONT = new Font(Font.SANS_SERIF, Font.BOLD, 24);

   private static void createAndShowGui() {
      JTextField field = new JTextField(10);
      field.setFont(BTN_FONT.deriveFont(Font.PLAIN));
      JPanel btnPanel = new JPanel(new GridLayout(BUTTON_TEXTS.length,
            BUTTON_TEXTS[0].length));

      for (int i = 0; i < BUTTON_TEXTS.length; i++) {
         for (int j = 0; j < BUTTON_TEXTS[i].length; j++) {
            JButton btn = new JButton(BUTTON_TEXTS[i][j]);
            btn.setFont(BTN_FONT);
            btnPanel.add(btn);
         }
      }

      JPanel mainPanel = new JPanel(new BorderLayout());
      mainPanel.add(field, BorderLayout.PAGE_START);
      mainPanel.add(btnPanel, BorderLayout.CENTER);


      JFrame frame = new JFrame("Calc2");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

You might like to study this example that follows the suggestions of @HFOE and @mre. Note that "size" appears nowhere in the code.