GridBagLayout Example

import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import javax.swing.*;

@SuppressWarnings("serial")
public class QuadEq2 extends JPanel {
    private static final String TITLE_TEXT = "Enter coefficients of the equation:";
    private static final int COL_COUNT = 10;
    private static final int GAP = 4;
    private static final Insets INSETS = new Insets(GAP, GAP, GAP, GAP);
    private JTextField aCoefTextField = new JTextField(COL_COUNT);
    private JTextField bCoefTextField = new JTextField(COL_COUNT);
    private JTextField cCoefTextField = new JTextField(COL_COUNT);
    private JTextField solutnTextField = new JTextField(COL_COUNT);
    private JButton jbtnSolve = new JButton(new QuadSolutionAction("Solve Equation"));

    public QuadEq2() {
        // make the solutnTextField non-editable
        solutnTextField.setFocusable(false);
        solutnTextField.setEditable(false);

        setBorder(BorderFactory.createEmptyBorder(GAP, GAP, GAP, GAP));
        setLayout(new GridBagLayout());

        // constraints for the title
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridx = 0;
        gbc.gridy = 0;
        gbc.gridwidth = 2;
        gbc.fill = GridBagConstraints.BOTH;
        gbc.weightx = 1.0;
        gbc.weighty = 1.0;
        gbc.anchor = GridBagConstraints.CENTER;
        gbc.insets = INSETS;
        JLabel titleLabel = new JLabel(TITLE_TEXT, SwingConstants.CENTER);
        add(titleLabel, gbc);

        // add coefficient JTextFields with JLabel to
        // each row in the grid
        addCoeffField(1, "A", aCoefTextField);
        addCoeffField(2, "B", bCoefTextField);
        addCoeffField(3, "C", cCoefTextField);

        // add solution button and text field to the last row
        addTwoComps(4, jbtnSolve, solutnTextField);
    }

    private void addCoeffField(int row, String text, JTextField coefTextField) {
        JLabel label = new JLabel("Coefficient " + text + ":");
        addTwoComps(row, label, coefTextField);
    }

    private void addTwoComps(int row, JComponent comp1, JComponent comp2) {
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridx = 0;
        gbc.gridy = row;
        gbc.fill = GridBagConstraints.BOTH;
        gbc.weightx = 1.0;
        gbc.weighty = 1.0;
        gbc.anchor = GridBagConstraints.WEST;
        Insets insets = INSETS;
        insets.right = 2 * GAP;
        gbc.insets = insets;
        add(comp1, gbc);

        gbc.gridx = 1;
        gbc.insets = INSETS;
        gbc.fill = GridBagConstraints.HORIZONTAL;
        gbc.anchor = GridBagConstraints.EAST;
        add(comp2, gbc);
    }

    private class QuadSolutionAction extends AbstractAction {
        public QuadSolutionAction(String name) {
            super(name);
            // give the button a mnemonic alt-key
            int mnemonic = (int) name.charAt(0);
            putValue(MNEMONIC_KEY, mnemonic);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            // TODO put code to do calculation here
            // output to the solutnTextField
        }
    }

    private static void createAndShowGui() {
        QuadEq2 mainPanel = new QuadEq2();

        JFrame frame = new JFrame("Solve Equation");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}