Измените размер JTable, чтобы он соответствовал количеству строк

Я не думаю, что это лучший способ. Но, как вы настаиваете, я поставил код ниже.

import javax.swing.RowFilter;
import javax.swing.table.DefaultTableModel;
import javax.swing.table.TableRowSorter;

/**
 *
 * @author user
 */
public class MyFrame extends javax.swing.JFrame {

    private DefaultTableModel model = null;

    TableRowSorter<DefaultTableModel> sorter = null;

    /**
     * Creates new form MyFrame
     */
    public MyFrame() {
        initComponents();
        model = new DefaultTableModel(null, new String[]{
            "Name", "age", "salary"
        });
        jTable1.setModel(model);
        for (int i = 0; i < 10; i++) {
            model.addRow(new Object[]{"Beniton", 34, 10000});
            model.addRow(new Object[]{"Joema", 33, 10000});
        }
        sorter = new TableRowSorter<DefaultTableModel>(model);
        jTable1.setRowSorter(sorter);
        int rowCount = model.getRowCount();
        this.setSize(this.getWidth(), 50+ (jTable1.getRowHeight()*(rowCount+1)));
    }

    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {
        java.awt.GridBagConstraints gridBagConstraints;

        jLabel1 = new javax.swing.JLabel();
        searchBox = new javax.swing.JTextField();
        jTable1 = new javax.swing.JTable();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        getContentPane().setLayout(new java.awt.GridBagLayout());

        jLabel1.setText("Search");
        getContentPane().add(jLabel1, new java.awt.GridBagConstraints());

        searchBox.setMaximumSize(new java.awt.Dimension(150, 20));
        searchBox.setMinimumSize(new java.awt.Dimension(150, 20));
        searchBox.setName("searchField"); // NOI18N
        searchBox.setPreferredSize(new java.awt.Dimension(150, 20));
        searchBox.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                searchBoxActionPerformed(evt);
            }
        });
        gridBagConstraints = new java.awt.GridBagConstraints();
        gridBagConstraints.gridx = 1;
        gridBagConstraints.gridy = 0;
        gridBagConstraints.anchor = java.awt.GridBagConstraints.WEST;
        gridBagConstraints.weightx = 1.0;
        gridBagConstraints.insets = new java.awt.Insets(4, 4, 4, 4);
        getContentPane().add(searchBox, gridBagConstraints);
        searchBox.getAccessibleContext().setAccessibleName("");

        jTable1.setModel(new javax.swing.table.DefaultTableModel(
            new Object [][] {
                {null, null, null, null},
                {null, null, null, null},
                {null, null, null, null},
                {null, null, null, null}
            },
            new String [] {
                "Title 1", "Title 2", "Title 3", "Title 4"
            }
        ));
        gridBagConstraints = new java.awt.GridBagConstraints();
        gridBagConstraints.gridx = 0;
        gridBagConstraints.gridy = 1;
        gridBagConstraints.gridwidth = 2;
        gridBagConstraints.fill = java.awt.GridBagConstraints.BOTH;
        gridBagConstraints.weightx = 1.0;
        gridBagConstraints.weighty = 1.0;
        getContentPane().add(jTable1, gridBagConstraints);

        pack();
    }// </editor-fold>                        

    private void searchBoxActionPerformed(java.awt.event.ActionEvent evt) {                                          
        if (searchBox.getText().length() > 0) {
            Integer value = Integer.parseInt(searchBox.getText());
            // Checking the age as Index is 1
            RowFilter<DefaultTableModel, Integer> rf = RowFilter.numberFilter(RowFilter.ComparisonType.BEFORE, value, 1);
            sorter.setRowFilter(rf);
        } else {
            sorter.setRowFilter(null);
        }
    }                                         

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(MyFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(MyFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(MyFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(MyFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new MyFrame().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JLabel jLabel1;
    private javax.swing.JTable jTable1;
    private javax.swing.JTextField searchBox;
    // End of variables declaration                   
}

Переопределите getPreferredScrollableViewportSize(), чтобы вернуть кратное произведение высоты строки и количества строк. Каждый раз, когда добавляется строка, pack() закрывающее окно.

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.table.AbstractTableModel;

/**
 * @see http://stackoverflow.com/a/37343900/230513
 * @see http://stackoverflow.com/a/37318673/230513
 */
public class Test {

    private void display() {
        JFrame f = new JFrame("Test");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        class MyTableModel extends AbstractTableModel {

            private int n = 8;

            private void addRow() {
                n++;
                fireTableRowsInserted(n - 1, n - 1);
            }

            @Override
            public int getRowCount() {
                return n;
            }

            @Override
            public int getColumnCount() {
                return 4;
            }

            @Override
            public Object getValueAt(int rowIndex, int colIndex) {
                return "R" + rowIndex + ":C" + colIndex;
            }
        };
        MyTableModel model = new MyTableModel();
        JTable table = new JTable(model) {
            @Override
            public Dimension getPreferredScrollableViewportSize() {
                return new Dimension(super.getPreferredSize().width,
                    getRowHeight() * getRowCount());
            }
        };
        table.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
        f.add(new JScrollPane(table));
        f.add(new JButton(new AbstractAction("Add Row") {
            @Override
            public void actionPerformed(ActionEvent e) {
                model.addRow();
                f.pack();
            }
        }), BorderLayout.SOUTH);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Test()::display);
    }
}