How to add data to DB using swing and MySQL?

Question

I have created MySQL DB and a Java GUI app using SWING . I have managed to add data to DB via SWING GUI for some tables but for some that have Foreign keys (at least i think that is why) i cant add data. It is probably something wrong with the FK or the table or with the methods i wrote to add the data to DB...

Here are my model , GUI classes ,MySQL table information and methods i try to use to add data to DB :

Model PRODUCT class :

package myshop.model;
public class Product {
    public int id;
    public String name;
    public Category category;
    public Manufacturer manufacturer;
    public Double price;
    public int quantity;
    public Product(int id,String name,Category category,Manufacturer manufacturer,Double price,int quantity){
        this.id = id;
        this.name = name;
        this.category = category;
        this.manufacturer = manufacturer;
        this.price = price;
        this.quantity = quantity;
    }
    @Override
    public String toString() {
        return this.name;
    }
}

Model CATEGORY class:

package myshop.model;
public class Category {
    public int id;
    public String name;
    public String description;
    public Category(int id,String name,String description){
        this.id = id;
        this.name = name;
        this.description = description;
}
    @Override
    public String toString() {
        return this.name;
    }
}

Model MANUFACTURER class :

package myshop.model;
public class Manufacturer {
    public int id;
    public String name;
    public String description;
    public Manufacturer(int id,String name,String description){
        this.id = id;
        this.name = name;
        this.description = description;
    }
    @Override
    public String toString() {
        return this.name;
    }
}

GUI class where i have created GUI for adding data to DB(questionable code is in jButton1actionpreformed):

    package myshop.gui;
    import java.sql.SQLException;
    import java.util.List;
    import java.util.logging.Level;
    import java.util.logging.Logger;
    import javax.swing.JOptionPane;
    import myshop.model.Category;
    import myshop.model.Manufacturer;
    import myshop.model.MyShopRepository;
    import myshop.model.Product;

    public class AddProductPanel extends javax.swing.JPanel {

        public AddProductPanel() throws SQLException {
        initComponents();
        MyShopRepository repo = MyShopRepository.getInstance();
        List<Category> cat = repo.getCategories();
        for(Category c : cat){
            cbKategorija.addItem(c);
        }
        List<Manufacturer> man = repo.getManufactureres();
        for(Manufacturer m : man){
            cbProizvodjac.addItem(m);
        }
    }
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

    jLabel1 = new javax.swing.JLabel();
    jLabel2 = new javax.swing.JLabel();
    tfNaziv = new javax.swing.JTextField();
    jLabel3 = new javax.swing.JLabel();
    cbKategorija = new javax.swing.JComboBox<>();
    jLabel4 = new javax.swing.JLabel();
    cbProizvodjac = new javax.swing.JComboBox<>();
    jLabel5 = new javax.swing.JLabel();
    tfCena = new javax.swing.JFormattedTextField();
    jLabel6 = new javax.swing.JLabel();
    spKolicina = new javax.swing.JSpinner();
    jButton1 = new javax.swing.JButton();

    jLabel1.setFont(new java.awt.Font("Tahoma", 0, 24)); // NOI18N
    jLabel1.setHorizontalAlignment(javax.swing.SwingConstants.CENTER);
    jLabel1.setText("Nov Proizvod");

    jLabel2.setText("Naziv :");

    jLabel3.setText("Kategorija :");

    jLabel4.setText("Proizvodjac :");

    jLabel5.setText("Cena :");

    jLabel6.setText("Kolicina :");

    jButton1.setText("Dodaj");
    jButton1.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jButton1ActionPerformed(evt);
        }
    });

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this);
    this.setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addComponent(jLabel1, javax.swing.GroupLayout.DEFAULT_SIZE, 400, Short.MAX_VALUE)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
                .addComponent(jLabel2)
                .addComponent(tfNaziv)
                .addComponent(jLabel3)
                .addComponent(cbKategorija, 0, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addComponent(jLabel4)
                .addComponent(cbProizvodjac, 0, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addComponent(jLabel5)
                .addComponent(tfCena)
                .addComponent(jLabel6)
                .addComponent(spKolicina, javax.swing.GroupLayout.DEFAULT_SIZE, 100, Short.MAX_VALUE))
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
            .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 100, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addContainerGap())
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addComponent(jLabel1)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(jLabel2)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(tfNaziv, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(jLabel3)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(cbKategorija, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(jLabel4)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(cbProizvodjac, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(jLabel5)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(tfCena, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(jLabel6)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(spKolicina, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 33, javax.swing.GroupLayout.PREFERRED_SIZE))
            .addGap(0, 28, Short.MAX_VALUE))
        );
    }// </editor-fold>                        

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    try {
        MyShopRepository repo = MyShopRepository.getInstance();
        repo.addProduct(new Product(0,
                                    tfNaziv.getText(),
                                   ((Category)cbKategorija.getSelectedItem()),
                                    ((Manufacturer)cbProizvodjac.getSelectedItem()),
                                    Double.parseDouble(tfCena.getValue().toString()),
                                    Integer.parseInt(spKolicina.getValue().toString())));
        JOptionPane.showMessageDialog(this, "Snimljeno","Uspesno snimanje",JOptionPane.INFORMATION_MESSAGE);
        MainForm.mainForm.changeContent(new ListProductsPanel());
    } catch (SQLException ex) {
        Logger.getLogger(AddProductPanel.class.getName()).log(Level.SEVERE, null, ex);
        }
    }                                        

    // Variables declaration - do not modify                     
    private javax.swing.JComboBox<Category> cbKategorija;
    private javax.swing.JComboBox<Manufacturer> cbProizvodjac;
    private javax.swing.JButton jButton1;
    private javax.swing.JLabel jLabel1;
    private javax.swing.JLabel jLabel2;
    private javax.swing.JLabel jLabel3;
    private javax.swing.JLabel jLabel4;
    private javax.swing.JLabel jLabel5;
    private javax.swing.JLabel jLabel6;
    private javax.swing.JSpinner spKolicina;
    private javax.swing.JFormattedTextField tfCena;
    private javax.swing.JTextField tfNaziv;
    // End of variables declaration                   
}

The class where i have connected to DB and where are methods i try to use to add data to DB(there are a lot of methods here but i will only add addProduct() method): Connection to DB:

    public class MyShopRepository {
private MyShopRepository() throws SQLException{
   conn = DriverManager.getConnection("jdbc:mysql://localhost/myshop","root","2007991710126");
}
private static MyShopRepository instance;
private final Connection conn;
public static MyShopRepository getInstance() throws SQLException{
    if(instance==null){
        instance = new MyShopRepository();
    }
    return instance;
}

The addProduct() method :

    public void addProduct(Product pr) throws SQLException{
    PreparedStatement ps = conn.prepareStatement("insert into product values (null,?,?,?,?,?)", PreparedStatement.RETURN_GENERATED_KEYS);
    ps.setString(1,pr.name);
    ps.setInt(2,pr.category.id);
    ps.setInt(3, pr.manufacturer.id);
    ps.setDouble(4, pr.price);
    ps.setInt(5, pr.quantity);
    ps.execute();
    if(ps.getUpdateCount()>0){
        ResultSet rs = ps.getGeneratedKeys();
        rs.next();
        pr.id = rs.getInt(1);
    }
}

MySQL that created tables:

    CREATE TABLE `myshop`.`category` (
    `id` INT NOT NULL AUTO_INCREMENT,
    `name` VARCHAR(45) NULL,
    `description` VARCHAR(45) NULL,
    PRIMARY KEY (`id`));

    CREATE TABLE `myshop`.`manufacturer` (
    `id` INT NOT NULL AUTO_INCREMENT,
    `name` VARCHAR(45) NULL,
    `description` VARCHAR(45) NULL,
    PRIMARY KEY (`id`));

    CREATE TABLE `myshop`.`product` (
    `id` INT NOT NULL AUTO_INCREMENT,
    `name` VARCHAR(45) NULL,
    `category` INT NULL,
    `manufacturer` INT NULL,
    `price` DECIMAL(7,2) NULL,
    `quantity` INT NULL,
    PRIMARY KEY (`id`),
    INDEX `fk_pro_cat_idx` (`category` ASC),
    INDEX `fk_pro_man_idx` (`manufacturer` ASC),
    CONSTRAINT `fk_pro_cat`
    FOREIGN KEY (`category`)
    REFERENCES `myshop`.`category` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
    CONSTRAINT `fk_pro_man`
    FOREIGN KEY (`manufacturer`)
    REFERENCES `myshop`.`manufacturer` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION);

This is the error i get when i click "Dodaj" button(jButton1) in the GUI :

    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at myshop.gui.AddProductPanel.jButton1ActionPerformed(AddProductPanel.java:119)
        at myshop.gui.AddProductPanel.access$000(AddProductPanel.java:12)
        at myshop.gui.AddProductPanel$1.actionPerformed(AddProductPanel.java:60)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
        at java.awt.Component.processMouseEvent(Component.java:6535)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
        at java.awt.Component.processEvent(Component.java:6300)
        at java.awt.Container.processEvent(Container.java:2236)
        at java.awt.Component.dispatchEventImpl(Component.java:4891)
        at java.awt.Container.dispatchEventImpl(Container.java:2294)
        at java.awt.Component.dispatchEvent(Component.java:4713)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
        at java.awt.Container.dispatchEventImpl(Container.java:2280)
        at java.awt.Window.dispatchEventImpl(Window.java:2750)
        at java.awt.Component.dispatchEvent(Component.java:4713)
        at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
        at java.awt.EventQueue.access$500(EventQueue.java:97)
        at java.awt.EventQueue$3.run(EventQueue.java:709)
        at java.awt.EventQueue$3.run(EventQueue.java:703)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
        at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
        at java.awt.EventQueue$4.run(EventQueue.java:731)
        at java.awt.EventQueue$4.run(EventQueue.java:729)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

Whats the problem , and how do i get this to work ?

All that code and text, and it's just a NullPointerException or NPE, and likely has little to do with most of the code and text you've posted. Have you searched on this exception prior to posting? The canonical answer will likely help you fix it. — Hovercraft Full Of Eels, Sep 04 '16 at 21:03
You're missing the most important part of the question: Which line is the offending line? — Hovercraft Full Of Eels, Sep 04 '16 at 21:05
[Google link to many, many similar NPE questions](https://www.google.com/search?q=site%3Astackoverflow.com%20java&rct=j#q=site:http:%2F%2Fstackoverflow.com+java+nullpointerexception) — Hovercraft Full Of Eels, Sep 04 '16 at 21:19
So again, which line is 119? Only you can tell, since you've got the code with the necessary line numbers. — Hovercraft Full Of Eels, Sep 04 '16 at 21:20
Oh its : repo.addProduct(new Product(0, -in the AddProductPanel class.. oh w8 nooo its this one : Double.parseDouble(tfCena.getValue().toString()), — Aleksandar Stojanovic, Sep 04 '16 at 21:22
Something on that line is null -- either use a debugger to find out which, or break that line up into its constituent parts -- extract each piece of parameter data on its own line -- to find out which part is causing your error. — Hovercraft Full Of Eels, Sep 04 '16 at 21:24
Are you checking to be sure that the combo box has a valid selection before extracting? Same for the JFormattedTextField? — Hovercraft Full Of Eels, Sep 04 '16 at 21:27
OK so the problem is that i passed a parameter to the Product constructor which has the value of null and its supposed to have some value ? And its most likely to be a value from CB or TF.. — Aleksandar Stojanovic, Sep 04 '16 at 21:48
Don't guess -- test! Either use a debugger or a "poor-man's debugger" (a bunch of println statements before the offending line) to find out what's null. Something is. — Hovercraft Full Of Eels, Sep 04 '16 at 21:49
@HovercraftFullOfEels OK so , i replaced jFormatedTextField with a jTextField and i inputed double into it and it works , how come it wont work with formated , format is by default number #,##0.### ? — Aleksandar Stojanovic, Sep 04 '16 at 22:28
That's a separate question, and I suggest that you ask it, but in doing so, and in the future, strive to ask in an isolated fashion, without all the other unrelated and distracting code. Please have a look at the [mcve] specification, and consider creating one for this question, one that shows how you've set up the format mask, and demonstrates how it's not working. — Hovercraft Full Of Eels, Sep 04 '16 at 22:35

How to add data to DB using swing and MySQL?

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