Question

Here is my code, but the frame shows an empty window and no error (syntax or another). I think it is some error in the JPanel or GridLayout. When I put my mouse on GridLayout on p1.setLayout(new GridLayout(2,2)); it shows "Note:This element has no attached source and the Javadoc could not be found in the attached javadoc".

This is test

  import javax.swing.JFrame;


  public class test {

    public static void main(String[] args) {

        menu frame = new menu();
        frame.setTitle("menu");
        frame.setSize(400,400);
        frame.setLocationRelativeTo(null);// Center the frame 
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);     
    }
  }

And my code

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;

import javax.swing.Box;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;


public class menu extends JFrame{

JButton jbtAdd = new JButton("add");
JButton jbtPrint = new JButton("print");

ArrayList<Product> manu = new ArrayList<Product>();


public void menu(){

    JPanel p1=new JPanel();

    p1.setLayout(new GridLayout(2,2));

    p1.add(new JLabel("add new product"));
    p1.add(jbtAdd);
    p1.add(new JLabel("print menu"));
    p1.add(jbtPrint);

    JPanel p2=new JPanel(new BorderLayout());
    p2.add(new JTextField("MENU"), BorderLayout.NORTH);

    p2.add(p1,BorderLayout.CENTER );

    add(p2, BorderLayout.SOUTH);

    jbtAdd.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            JOptionPaneMultiInput input=new JOptionPaneMultiInput();    
        }
    }); 
};


public class JOptionPaneMultiInput {

    public void JOptionPaneMultiInput(){

    JTextField productField = new JTextField(5);
    JTextField priceField = new JTextField(5);

    JPanel myPanel = new JPanel();
    myPanel.add(new JLabel("enter product"));
    myPanel.add(productField);
    myPanel.add(Box.createHorizontalStrut(15)); // a spacer
    myPanel.add(new JLabel("enter price"));
    myPanel.add(priceField);

    int result=  JOptionPane.showConfirmDialog(null, myPanel, 
         "Please Enter product and price Values", JOptionPane.OK_CANCEL_OPTION);

    String name1= productField.getText();

    double price1=Double.parseDouble(priceField.getText());

    if (result == JOptionPane.OK_OPTION) {            
       Product name  = new Product(name1, price1);
         manu.add(name);
    } 

  }
}

private class Product{

    private String name = "noname";
    private Double price=new Double(100);

    public Product(String name1, double price1) {
        // TODO Auto-generated constructor stub
    }

    public void Product(){
        };

    public void Product(String name,double price)
    {
        this.name=name;
        this.price=price;
    };

    public double getPrice(){
    return price;}

    public void setPrice(Double p){
        price=p;}

    public String getName(){
        return name;}

    public void setName(String n){
        name=n;}

  } 
}

Answer 1

You currently have an extra void keyword in your constructor, effectively making it a method, therefore it is never called. Replace

public void menu() {

with

public menu() {

Similarly for Product, replace

public void Product() {

with

public Product() {

Aside: Java Code Conventions indicate that class names start with a capital letter which give you a Menu class.