adding data to a JTable from another Form in netbeans

From comments section:

CurrentPurchases.getModel() underlined with red. Actually CurrentPurchases is the name of the jtable in the other form. So what should I do now?

I understand your problem now. You're trying to access a variable defined in a form from another form directly. That's why the compiler is complaining. You'll need to create a public getter to this CurrentPurchases in order to access it from other class. Something like this:

public JTable getCurrentPurchasesTable() {
    return this.CurrentPurchases;
}

Then make this change:

DefaultTableModel CurrPurchases= (DefaultTableModel) otherFormVariable.getCurrentPurchasesTable().getModel();

Of course you'll need a reference to the other form (I called it otherFormVariable in the example) in order to get the table as you wish.

An off-topic tip:

• Always try to follow Java Code Conventions. It makes people talk the same language.

Edit: implementation examples

Well as you're new to Java (welcome to this world :P) I'll give you two possible implementation examples.

First off let's say you have 2 forms as follows:

• Form1: here is placed your table.
• Form2: here you can add a new record to your DB and the previous table.

Example 1: Giving public access to Form1's table

The first way is the one you're trying. To make it work in this way you'll need do something like this:

public class Form1 extends JDialog {

    JTable currentPurchases;
    JButton addRecordButton;

    private initComponents() {
        addRecordButton = new JButton("Add record");
        addRecord.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent evt) {
                Form2 form2 = new Form2();
                form2.setForm1(this);
                form2.setVisible(true);
            }
        };
        ... // init the table and other components
    }

    public JTable getCurrentPurchasesTable() {
        return this.currentPurchases;
    }
}

public class Form2 extends JDialog {

    Form1 form1; // this variable will keep reference to a Form1 instance
    JButton saveRecordButton;

    private void initComponents() {
        saveRecordButton = new JButton("Save record");
        saveRecordButton .addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent evt) {
                DefaultTableModel model = (DefaultTableModel) form1.getCurrentPurchasesTable().getModel();
                // add new rocord to the model
            }
        };
        ... // init the other components

    }

    public void setForm1(Form1 f) {
        this.form1 = f;
    }

}

Example 2: Setting a TableModel to Form2

This second way is about setting a TableModel to the Form2 object. This way you don't need public access to your table anymore. It should be something like this:

public class Form1 extends JDialog {

    JTable currentPurchases;
    JButton addRecordButton;

    private initComponents() {
        addRecordButton = new JButton("Add record");
        addRecord.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent evt) {
                Form2 form2 = new Form2();
                form2.setTableModel(currentPurchases.getModel());
                form2.setVisible(true);
            }
        };
        ... // init the table and other components
    }
}

public class Form2 extends JDialog {

    TableModel model; // this variable will keep reference to a TableModel instance
    JButton saveRecordButton;

    private void initComponents() {
        saveRecordButton = new JButton("Save record");
        saveRecordButton .addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent evt) {
                // add new rocord to the model:
                ((DefaultTableModel)model).addRow(...);                    
            }
        };
        ... // init the other components

    }

    public void setTableModel(TableModel m) {
        this.model = m;
    }

}