Position Buttons Scaled Table Using Layouts Manager

Question

I’m having trouble positioning components. I have a table, and 3 buttons, and I’m trying to place the buttons above the table centrally.

Example:

I tried to use the FlowLayout, and the result was this:

import java.awt.Dimension;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;

public class PosicionaTabela extends JFrame {

    public PosicionaTabela() {

        Tabela tab = new Tabela();
        add(tab);
        setSize(700, 400);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
    }

    public static void main(String[] args) {
        new PosicionaTabela().setVisible(true);
    }
}

class Tabela extends JPanel {

    private JScrollPane jsp = new JScrollPane();

    private JTable tabela = new JTable();

    private JButton botao1 = new JButton("1");
    private JButton botao2 = new JButton("2");
    private JButton botao3 = new JButton("3");

    public Tabela() {
        confgTabela();
    }

    private JComponent confgTabela() {
        JPanel painel = new JPanel();
        jsp.setViewportView(tabela);
        jsp.setPreferredSize(new Dimension(400, 200));
        add(jsp);
        add(botao1);
        add(botao2);
        add(botao3);
        return painel;
    }
}

Answer 1

I did so, using a BorderLayout to help:

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;

public class PosicionaTabela extends JFrame {

    public PosicionaTabela() {
        Tabela tab = new Tabela();
        add(tab);
        setSize(700, 400);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> new PosicionaTabela().setVisible(true));
    }
}

class Tabela extends JPanel {

    private JScrollPane jsp = new JScrollPane();

    private JTable tabela = new JTable();

    private JButton botao1 = new JButton("1");
    private JButton botao2 = new JButton("2");
    private JButton botao3 = new JButton("3");

    public Tabela() {
        JPanel painel = new JPanel();
        jsp.setViewportView(tabela);
        jsp.setPreferredSize(new Dimension(400, 200));
        this.setLayout(new BorderLayout());
        add(jsp, BorderLayout.CENTER);
        add(painel, BorderLayout.NORTH);
        painel.add(botao1);
        painel.add(botao2);
        painel.add(botao3);
    }
}

That is the result:

About the EventQueue.invokeLater(...), see more about this in that other answer.

Answer 2

I got this in your code by modifying as below:

import java.awt.BorderLayout;
import java.awt.Dimension;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;

public class PosicionaTabela extends JFrame {

    private JScrollPane jsp = new JScrollPane();

    private JTable tabela = new JTable();

    private JButton botao1 = new JButton("1");
    private JButton botao2 = new JButton("2");
    private JButton botao3 = new JButton("3");

    public PosicionaTabela() {

        getContentPane().add(getButtonsPanel(), BorderLayout.NORTH);
        getContentPane().add(getTabelaPanel(), BorderLayout.CENTER);
        setSize(700, 400);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
    }

    private JPanel getTabelaPanel() {
        JPanel painel = new JPanel();
        jsp.setViewportView(tabela);
        jsp.setPreferredSize(new Dimension(400, 200));
        painel.add(jsp);
        return painel;
    }

    private JPanel getButtonsPanel(){       
        JPanel painel = new JPanel();
        painel.add(botao1);
        painel.add(botao2);
        painel.add(botao3);
        return painel;
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> new PosicionaTabela().setVisible(true));
    }
}

There are some problems in the code, as you create a JPanel and return it but add nothing to it. I created a panel to return the JScrollPane just to illustrate but it is not even necessary, since this class is already a container by itself and can be added directly to the JFrame.

More information about Layout Managers can be found on Official guide to the oracle.