Reading Data From Database and storing in Array List object

You have to create a new customer object in every iteration and then add that newly created object into the ArrayList at the lase of your iteration.

Try with the following code

public static ArrayList<Customer> getAllCustomer() throws ClassNotFoundException, SQLException {
    Connection conn=DBConnection.getDBConnection().getConnection();
    Statement stm;
    stm = conn.createStatement();
    String sql = "Select * From Customer";
    ResultSet rst;
    rst = stm.executeQuery(sql);
    ArrayList<Customer> customerList = new ArrayList<>();
    while (rst.next()) {
        Customer customer = new Customer(rst.getString("id"), rst.getString("name"), rst.getString("address"), rst.getDouble("salary"));
        customerList.add(customer);
    }
    return customerList;
}

this is my model class

public class Customer {
private String id;
private String name;
private String salary;
private String address;
public String getId() {
    return id;
}
public void setId(String id) {
    this.id = id;
}
public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}
public String getSalary() {
    return salary;
}
public void setSalary(String salary) {
    this.salary = salary;
}
public String getAddress() {
    return address;
}
public void setAddress(String address) {
    this.address = address;
}
}

this is my view method

  private void reloadButtonActionPerformed(java.awt.event.ActionEvent evt) {                                             
    try {
        ArrayList<Customer> customerList = null;
        try {
            try {
                customerList = CustomerController.getAllCustomer();
            } catch (SQLException ex) {
                Logger.getLogger(veiwCustomerFrame.class.getName()).log(Level.SEVERE, null, ex);
            }
        } catch (Exception ex) {
            Logger.getLogger(ViewCustomerForm.class.getName()).log(Level.SEVERE, null, ex);
        }
        DefaultTableModel tableModel = (DefaultTableModel) customerTable.getModel();
        tableModel.setRowCount(0);
        for (Customer customer : customerList) {
            Object rowData[] = {customer.getId(), customer.getName(), customer.getAddress(), customer.getSalary()};
            tableModel.addRow(rowData);
        }


    } catch (Exception ex) {
        Logger.getLogger(ViewCustomerForm.class.getName()).log(Level.SEVERE, null, ex);
    }

}