Why does my really simple java program sometimes work and sometimes it doesn’t work?

I've just started using Java and only used PHP before - it's hard to find object - oriented things I am using the eclipse ide

I'm trying to make a program that can tell you the weight on another planet - it looks simple

What I have done so far is to create half the interface in swing (this is called?)

Sometimes I run it and it will appear as I expected, title, text box, etc Other times (when absolutely nothing has changed), it will only show a blank screen

The image shows how it works When it doesn't work, there are no objects It works about 20% of the time

I think this may be because of my drop-down menu – or JCombo@R_939_2419 @, this has always been a headache – eclipse asked me to add "< Object >" every time I mentioned it JCombo@R_939_2419 @After – it says“ JCombo@R_939_2419 @Is the original type For generic types JCombo@R_939_2419 @References to should be parameterized

I don't know why, and I may just be really thick. Sorry, if this is a stupid problem, but how can I solve this problem and 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 @R_939_2419@es and Lists
    JTextField txtInputMass = new JTextField(5);

    JCombo@R_939_2419@<Object> comInputUnits;
    String arrUnits[] = {"Kilos","Stone","Pounds"};
    comInputUnits = new JCombo@R_939_2419@<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, this is a long question, and I will be very grateful for any suggestions or answers. As I said, I know about Java barley, I've just started - thank you:)

Solution

You should

>Only manipulate swing components in event dispatch thread; > Setvisible (true) is called only after all components are added to the framework; > Spelling only one n planet, though not so important

< Object > "eclipse lets you add" is called a generic type Read tutorial on genetics