Porque o Insert abaixo não funciona?

connection.commit()

package cliente;

import javax.swing.SwingUtilities;

import java.awt.BorderLayout;

import javax.swing.JOptionPane;

import javax.swing.JPanel;

import javax.swing.JFrame;

import javax.swing.JButton;

import java.awt.Rectangle;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.ResultSet;

import javax.swing.JTextField;

import javax.swing.JLabel;

import java.awt.event.KeyEvent;

import javax.swing.JComboBox;

//para conectar
public cliente meucliente;
public clienteDAO meuclienteDAO;

private static final long serialVersionUID = 1L;
private JPanel jContentPane = null;
private JButton jButton = null;
private JTextField jTextField = null;
private JLabel jLabel = null;
/**
 * This method initializes jButton	
 * 	
 * @return javax.swing.JButton	
 */
private JButton getJButton() {
	if (jButton == null) {
		jButton = new JButton();
		jButton.setBounds(new Rectangle(186, 112, 79, 34));
		jButton.setMnemonic(KeyEvent.VK_UNDEFINED);
		jButton.setText("Enviar");
		jButton.setName("");
		
		jButton.addMouseListener(new java.awt.event.MouseAdapter() {
			public void mouseClicked(java.awt.event.MouseEvent e) {
				System.out.println("mouseClicked()"); // TODO Auto-generated Event stub mouseClicked()
				//Evento Onclic
				meucliente.setCodigo(Integer.parseInt(jTextField.getText()));
				
				//meucliente.validar();
				
				//if chamar o metodo da classe cliente e la chamar a classe Dao {
				meuclienteDAO.inserir(meucliente);
			}
		});
	}
	return jButton;
}

/**
 * This method initializes jTextField	
 * 	
 * @return javax.swing.JTextField	
 */
private JTextField getJTextField() {
	if (jTextField == null) {
		jTextField = new JTextField();
		jTextField.setBounds(new Rectangle(86, 16, 126, 25));
	}
	return jTextField;
}

/**
 * @param args
 */
public static void main(String[] args) {
	// TODO Auto-generated method stub
	SwingUtilities.invokeLater(new Runnable() {
		public void run() {
			clientemain thisClass = new clientemain();
			thisClass.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
			thisClass.setVisible(true);
		}
	});
}

/**
 * This is the default constructor
 */
public clientemain() {
	super();
	meucliente = new cliente();
	meuclienteDAO = new clienteDAO();
	initialize();
}

/**
 * This method initializes this
 * 
 * @return void
 */
private void initialize() {
	this.setSize(300, 200);
	this.setContentPane(getJContentPane());
	this.setTitle("JFrame");
}

/**
 * This method initializes jContentPane
 * 
 * @return javax.swing.JPanel
 */
private JPanel getJContentPane() {
	if (jContentPane == null) {
		jLabel = new JLabel();
		jLabel.setBounds(new Rectangle(11, 14, 63, 28));
		jLabel.setText("Nome");
		jContentPane = new JPanel();
		jContentPane.setLayout(null);
		jContentPane.add(getJButton(), null);
		jContentPane.add(getJTextField(), null);
		jContentPane.add(jLabel, null);
	}
	return jContentPane;
}

JOptionPane.showMessageDialog(null,"insert into cliente (codigo) values (" + clientelocal.getCodigo() + ") ");

public static void main(String[]args)
{

	final String DRIVER = "org.postgresql.Driver";
	final String URL = "jdbc:postgresql://localhost:5432/postgres?user=postgres&password=123456";
    
	try
	{
		Class.forName(DRIVER);
		Connection connection = DriverManager.getConnection(URL);
		JOptionPane.showMessageDialog(null," Conexao realizada com sucesso");
		
	}
	catch(ClassNotFoundException erro)
	{
		JOptionPane.showMessageDialog(null,"problemas driver nao encontrado");
	}	
	catch(SQLException erro)
	{
		JOptionPane.showMessageDialog(null,"problemas na conexao 1");
	}	
	
}

final String URL = "jdbc:postgresql://localhost:5432/sac?user=postgres&password=123456";