Space between buttons and window

问题:

I have this code right here, and the idea is to have two buttons in a main window alongside a text area, which I have not added yet. After trying to use GridBagLayout and ripping off my hair in the process I decided not to use a layout and manually position buttons inside a non resizable window.

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class Tema extends JFrame implements ActionListener {

JMenuBar menubar = new JMenuBar();
JMenu actiuni = new JMenu("Actiuni");
JMenu contact = new JMenu("Contact");
JMenu help = new JMenu("Help");
JMenuItem ntest = new JMenuItem("Nou test");
JMenuItem vizarh = new JMenuItem("Vizualizare arhiva");
JMenuItem datcon = new JMenuItem("Date de contact");
JMenuItem sendmail = new JMenuItem("Trimite e-mail");
JMenuItem instrut = new JMenuItem("Instructiuni de utilizare");
JButton b1 = new JButton("Incepe testul!");
JButton b2 = new JButton("Vezi arhiva!");
JTextArea ta = new JTextArea("Default text", 5, 30);

public void common(String s)
{
    setSize(800,450);
    setLocationRelativeTo(null);
    setResizable(false);

    setTitle(s);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);


    menubar.add(actiuni);
    menubar.add(contact);
    menubar.add(help);
    actiuni.add(ntest);
    actiuni.add(vizarh);
    contact.add(datcon);
    contact.add(sendmail);
    help.add(instrut);

    setJMenuBar(menubar);

}

public Tema()
{
    common("Self-Esteem- Fereastra Principala");
    JPanel cp = new JPanel();
    cp.setLayout(null);


    b1.setBounds(100,100,200,100);
    cp.add(b1);


    b2.setBounds(100,250,200,100);
    cp.add(b2);

    setContentPane(cp);
    setVisible(true);

}

public static void main(String[] args)
{
    Tema x = new Tema();
}


@Override
public void actionPerformed (ActionEvent e){           

}

}

But the output is this:

My question is why isn't the space beneath the second button equal to the space above the first button? Shouldn't they both be 100 pixels?

回答1:

• Don't extend JFrame class unnecessarily.
• Never use Absolute/Null LayoutManager. Use an appropriate LayoutManager, this includes nesting Layouts to achieve desired look. see here for good tutorials:
  • A Visual Guide to Layout Managers
  • Using Layout Managers
• Don't call JFrame#setSize(..) on JFrame rather just call JFrame#pack() before setting JFrame visible.
• Dont use JFrame#setContentPane(...) just use add(..) on JFrame instance
• Create Event Dispatch Thread to initialize and change UI components
• Don't implement single ActionListener for multiple components. Unless it will be accessed by other class(es) or components share a Action. Rather use an Anonymous ActionListener

Here is an example I made (basically your code fixed) hope it helps:

import java.awt.BorderLayout;
import java.awt.GridLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;

public class LayoutTest {

    private final JMenuBar menubar = new JMenuBar();
    private final JMenu actiuni = new JMenu("Actiuni");
    private final JMenu contact = new JMenu("Contact");
    private final JMenu help = new JMenu("Help");
    private final JMenuItem ntest = new JMenuItem("Nou test");
    private final JMenuItem vizarh = new JMenuItem("Vizualizare arhiva");
    private final JMenuItem datcon = new JMenuItem("Date de contact");
    private final JMenuItem sendmail = new JMenuItem("Trimite e-mail");
    private final JMenuItem instrut = new JMenuItem("Instructiuni de utilizare");
    private final JButton b1 = new JButton("Incepe testul!");
    private final JButton b2 = new JButton("Vezi arhiva!");
    private final JTextArea ta = new JTextArea("Default text", 5, 30);
    //create JFrame instance
    private final JFrame frame = new JFrame();

    public LayoutTest() {
        initComponents();
    }

    public static void main(String[] args) {
        //creat UI on EDT
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new LayoutTest();
            }
        });
    }

    private void initComponents() {
        frame.setTitle("Self-Esteem- Fereastra Principala");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        menubar.add(actiuni);
        menubar.add(contact);
        menubar.add(help);
        actiuni.add(ntest);
        actiuni.add(vizarh);
        contact.add(datcon);
        contact.add(sendmail);
        help.add(instrut);

        frame.setJMenuBar(menubar);
        JPanel textAreaJPanel = new JPanel();

        //create button panel with GridLayout(2,1) 
        JPanel buttonJPanel = new JPanel(new GridLayout(2, 1));//new GridLayout(2, 1,10,10) creates gridlayout with horixontal and vertcial spacing of 10

        //add buttons to one panel
        buttonJPanel.add(b1);
        buttonJPanel.add(b2);
        //add text area to textarea jPanel
        textAreaJPanel.add(ta);

        //add textarea panel to west of content pane (BorderLayout by default)
        frame.add(textAreaJPanel, BorderLayout.WEST);

        //add button Panel to EAST of JFrame content pane
        frame.add(buttonJPanel, BorderLayout.EAST);

        frame.pack();

        frame.setResizable(false);
        frame.setLocationRelativeTo(null);

        frame.setVisible(true);
    }
}

回答2:

In the above code space between both the buttons is 50px, if you use b2.setBounds(100,300,200,100); then the space will be 100px. Try it...