Question

I’m just starting out in Java, and only ever used PHP before – finding it hard to get my head round the object-orientated thing. I am using the Eclipse IDE.

I am trying to make a program that will tell you your weight on another planet – seems simple enough

All I have done so far is make half the interface in Swing (is that what it’s called?)

Sometimes I run it, and it comes up as I would expect, with the title, textboxes etc….
other times (when absolutely no changes have been made), it just comes up with a blank screen

The image shows what it looks like when it is working. When it’s not working, there are just no objects. It works about 20% of the time.

I think this might have been because of my drop down menu – or JComboBox, this has been such a head ache – Eclipse made me add “< Object>” after each mention of JComboBox – it said “JComboBox is a raw type. References to generic type JComboBox should be parameterized”

I have no idea why this is, and I’m probably just being really thick, sorry if this is a stupid question, but how can I fix this problem, what’s wrong with my code?

package calc;

import javax.swing.*;
import java.awt.*;

public class View extends JFrame {

static String titleText = "Calculate your Mass on another Plannet";

public View(){
    super(titleText);
    setSize(500,400);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);

    FlowLayout flo = new FlowLayout();
    setLayout(flo);

    JPanel inputData = new JPanel();


    //Labels
    JLabel lblTitle = new JLabel (titleText, JLabel.CENTER);
    lblTitle.setFont(new Font("Arial", Font.BOLD, 24));
    JLabel lblInputMass = new JLabel ("Weight", JLabel.LEFT);
    JLabel lblInputUnits = new JLabel("Units");     


    //Input Boxes and Lists
    JTextField txtInputMass = new JTextField(5);

    JComboBox<Object> comInputUnits;
    String arrUnits[] = {"Kilos", "Stone", "Pounds"};
    comInputUnits = new JComboBox<Object>(arrUnits);
    comInputUnits.setSelectedIndex(1);


    //Buttons
    JButton btnCalculate = new JButton("Calculate");

    //Append objects
    add(lblTitle);
    inputData.add(lblInputMass);
    inputData.add(txtInputMass);
    inputData.add(lblInputUnits);
    inputData.add(comInputUnits);
    inputData.add(btnCalculate);

    add(inputData);


}
/**
 * @param args
 */
public static void main(String[] args) {
    View sal = new View();


}

}

Sorry it’s quite a long question, and I’d be so grateful to any suggestions or answers,
as I said, I know barley anything about Java, and am just starting out – thank you 🙂

Answer 1

You should

• only manipulate Swing components inside the event dispatch thread;
• call setVisible(true) only after all the components have been added to the frame;
• spell Planet with only one n, although that’s less important.

The <Object> that “Eclipse made you add” are called generic types. Read the tutorial on generics.