GUI在添加JComboBox时消失

Question

Alright I'm relatively new to programming and it may be just something simple that I'm missing but the other threads related to this topic the poster didn't give adequate information relative to their issue for others to provide quality answers so I will give it a shot.

public BenchUI(JFrame j){
    jf = j;
    init();     
    add(mainPanel);     
    topPanelButtons();  
    selectedCustomer();     
    rentalOptions();
    clientListBox();

}

At this point i can point out that everything works perfectly until I add the clientListBox() method. (below)

public void clientListBox(){
    clientList = new JComboBox(moo);
    clientList.setPreferredSize(new Dimension(460,30));
    gbc.gridx = 0;
    gbc.gridy = 0;
    leftSide.add(clientList,gbc);
}

i can comment it out and get my whole GUI back working perfectly but without a JComboBox.

moo is String [] moo = {"Fish","Goat", "Monkey"}; a dummy string just for testing purposes and initialized at the start.

So any idea why my GUI completely disappears when I place in the clientList?

If anything else is necessary I'll be watching this thread and can provide additional information.

As a side note I keep getting warnings for "Raw Types" but it works without specifiying, could I potentially run into trouble by not specifying my JComboBox?

EDIT:

ok I believe I've duplicated whatever the issue is in this code

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


public class main {

    public static void main(String[] args){
        JFrame jf = new JFrame();

        jf.setExtendedState(JFrame.MAXIMIZED_BOTH);
        jf.setVisible(true);
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jf.setResizable(false);

        BenchUI bu = new BenchUI(jf);
        jf.add(bu);
    }



}



    public class BenchUI extends JPanel{

    JPanel one;
    JFrame jf;
    JComboBox<String> clientList;
    String[] moo = {"Goat", "Fish", "Donkey"};

    public BenchUI(JFrame j){
        jf = j;

        one = new JPanel(new GridBagLayout());
        one.setBackground(Color.blue);
        one.setPreferredSize(new Dimension(300,300));

        clientList = new JComboBox<String>(moo);
        one.add(clientList);

        add(one);
    }
}

with the clientList stuff commented out I get my silly little blue panel and once it is added I lose the blue panel and the combobox doesnt show up as well...betting on this is a facepalm issue at this point >.<

EDIT: to include the main class.

EDIT: took out the comment marks for the JComboBox constructor and implementer

Answer 1

Your posted sort of sscce-like (not a real SSCCE by the way since we can't run it) code doesn't add any such as the JComboBox to the JPanel and adds no components such as the current JPanel to the JFrame.

public class BenchUI extends JPanel{

  JPanel one;
  JFrame jf;
  JComboBox<String> clientList;
  String[] moo = {"Goat", "Fish", "Donkey"};

  public BenchUI(JFrame j){
    jf = j;

    one = new JPanel(new GridBagLayout());
    one.setBackground(Color.blue);
    one.setPreferredSize(new Dimension(300,300));

    //clientList = new JComboBox<String>(moo);
    //one.add(clientList);

    add(one);
  }
}

and so it makes sense that none of the components will show up on any JFrame. You will want to read the Swing tutorials on how to add components to other components (or containers) and how to create and show a JFrame. Have a look at How to Use Swing Components .

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Edit
Your latest code now does in fact add the BenchUI JPanel to the JFrame, but still you add no components to the BenchUI JPanel, and in fact you don't even construct your JComboBox but only create a JComboBox variable. Again, I strongly urge you to read the Swing tutorials which I've linked to above as well as the general Java tutorials.

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Edit 2
Some general advice:

• If you want to add a component to a GUI you must first create the component object. You are declaring your clientList JComboBox, but you never create the object.
• Then you must add the component object to a container that eventually will be part of the hierarchy leading to a top level window such as a JFrame, JDialog, JApplet and such. You never add a clientList object to the GUI.
• You should add your components to the top level window before calling pack() on the top level window -- which tells all the layout managers to lay out all the components they hold.
• You should then call setVisible(true) . One problem with your code (other than not creating important components and not adding them to the GUI!) is that you're calling setVisible(true) on your JFrame way too early before adding anything to the GUI.
• Read the Swing tutorial, but especially the one on using layout managers and on adding components to a top level window.

  ---

Edit 3

OK, now you're creating your JComboBox, but you still are adding all components to your JFrame after setting it visible. Please re-check my 3rd and 4th bullets in the bullet list above.