java swing application - how to set the height (and width) of a component in a panel

Question

I'm writing a java swing application and I have a beginner's question, please.

The screen below is one of the 2 screens shown in the application. As you can see, there is a big space circled in red on the top of it. I can't get rid of it. I'd like it to be very short so that the "clear" button would touch the top of the frame.

I've tried a lot, but it didn't work. Can someone help?

This is the java code:

**import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ContainerEvent;
import java.awt.event.ContainerListener;
import java.util.Vector;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
public class ContainerEventDemo extends JPanel implements ContainerListener, ActionListener {
  JTextArea displayResource;

  JTextArea displayGateway;

  GridBagLayout gridbag = (GridBagLayout) getLayout();

  GridBagConstraints c = new GridBagConstraints();
  JScrollPane inputScrollPane;

  JScrollPane scrollPaneGateway;
  JScrollPane scrollPaneResource;
  JTextArea inputArea;
  JPanel mainPanel;
  JButton listReadButton, insertButton, deleteButton, updateButton, clearButton, allButton;
  Vector<JButton> buttonList;
  static final String LIST_READ = "list_read";

  static final String UPDATE = "update";

  static final String INSERT = "insert";
  static final String DELETE = "delete";
//  static final String REMOVE = "remove";
  static final String ALL = "all";
  static final String CLEAR = "clear";
  static final String newline = "\n";
  public ContainerEventDemo() {
    super(new GridBagLayout());
    // create all the components.
    listReadButton = new JButton("List and Read");
    listReadButton.setActionCommand(LIST_READ);
    listReadButton.addActionListener(this);
    insertButton = new JButton("Insert");
    insertButton.setActionCommand(INSERT);
    insertButton.addActionListener(this);
    deleteButton = new JButton("Delete");
    deleteButton.setActionCommand(DELETE);
    deleteButton.addActionListener(this);

    updateButton = new JButton("Update");
    updateButton.setActionCommand(UPDATE);
    updateButton.addActionListener(this);

    allButton = new JButton("All");
    allButton.setActionCommand(ALL);
    allButton.addActionListener(this);

    mainPanel = new JPanel(new GridLayout(1, 1));
//    mainPanel.setSize(400, 100);
//    mainPanel.setPreferredSize(new Dimension(400, 5));
    mainPanel.addContainerListener(this);
    inputArea = new JTextArea();
    inputArea.setEditable(true);
    inputScrollPane = new JScrollPane(inputArea);
//    inputScrollPane.setSize(200, 175); // x, y
//    inputScrollPane.setPreferredSize(new Dimension(200, 75)); // x, y
    clearButton = new JButton("Clear");
    clearButton.setActionCommand(CLEAR);
    clearButton.addActionListener(this);
    addComponents();
    setPreferredSize(new Dimension(800, 800));  //  X, Y
    setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
  }
  public void componentAdded(ContainerEvent e) {
//    displayMessage(" added to ", e);
  }
  public void componentRemoved(ContainerEvent e) {
 //   displayMessage(" removed from ", e);
  }
//  void displayMessage(String action, ContainerEvent e) {
//    displayGateway.append(((JButton) e.getChild()).getText() + " was" + action
//        + e.getContainer().getClass().getName() + newline);
//    displayGateway.setCaretPosition(displayGateway.getDocument().getLength());
//  }


  public void addComponents() {
        c.fill = GridBagConstraints.BOTH; // Fill entire cell.
        c.weighty = 22.0; // Button area and message area have equal height.
        c.gridwidth = GridBagConstraints.REMAINDER; // end of row
    //    c.gridheight = 40;
        gridbag.setConstraints(inputScrollPane , c);
        add(inputScrollPane);
        c.weighty = 0.0;
        c.weightx = 1.0; // Add/remove buttons have equal width.
        c.gridwidth = 1; // NOT end of row
        gridbag.setConstraints(listReadButton, c);
        add(listReadButton);
        c.gridwidth = GridBagConstraints.REMAINDER; // end of row
        gridbag.setConstraints(insertButton, c);
        add(insertButton);
        c.gridwidth = GridBagConstraints.REMAINDER; 
        c.gridwidth = 1; // NOT end of row
        gridbag.setConstraints(deleteButton, c);
        add(deleteButton);

        c.gridwidth = GridBagConstraints.REMAINDER; // end of row
        gridbag.setConstraints(updateButton, c);
        add(updateButton);
        c.gridwidth = GridBagConstraints.REMAINDER; // end of row
        gridbag.setConstraints(allButton, c);
        add(allButton);

        c.weighty = 1.0; // Button area and message area have equal height.
        gridbag.setConstraints(mainPanel, c);
        add(mainPanel);
  };
  /*
   * This could have been implemented as two or three classes or objects, for
   * clarity.
   */
  public void actionPerformed(ActionEvent e) {
    String command = e.getActionCommand();
    if (LIST_READ.equals(command) || UPDATE.equals(command) || INSERT.equals(command) || DELETE.equals(command) || ALL.equals(command)) {

        remove(inputScrollPane);
        remove(listReadButton);
        remove(insertButton);
        remove(deleteButton);
        remove(updateButton);
        remove(allButton);
//      mainPanel.revalidate(); // Make the button show up.
//      mainPanel.repaint(); // Make the button show up.

        c.fill = GridBagConstraints.BOTH; // Fill entire cell.
        c.gridwidth = GridBagConstraints.REMAINDER; // end of row
        c.weighty = 0.0;
        gridbag.setConstraints(clearButton, c);
        add(clearButton);
//      aKI
        displayGateway = new JTextArea();
        displayGateway.setEditable(false);
        scrollPaneGateway = new JScrollPane(displayGateway);
        scrollPaneGateway.setPreferredSize(new Dimension(200, 75));
        c.fill = GridBagConstraints.BOTH; // Fill entire cell.
        c.weighty = 1.0; // Button area and message area have equal height.
        c.gridwidth = GridBagConstraints.REMAINDER; // end of row
        gridbag.setConstraints(scrollPaneGateway, c);
        add(scrollPaneGateway);
        displayResource = new JTextArea();
        displayResource.setEditable(true);
        displayResource.setText("hahaha");
        scrollPaneResource = new JScrollPane(displayResource);
        scrollPaneResource.setPreferredSize(new Dimension(200, 75));
        c.fill = GridBagConstraints.BOTH; // Fill entire cell.
        c.weighty = 1.0; // Button area and message area have equal height.
        c.gridwidth = GridBagConstraints.REMAINDER; // end of row
        gridbag.setConstraints(scrollPaneResource, c);
        add(scrollPaneResource);
        mainPanel.revalidate(); // Make the button show up.


    } /*else if (REMOVE.equals(command)) {
      int lastIndex = buttonList.size() - 1;
      try {
          mainPanel.remove(displayResource);

        JButton nixedButton = buttonList.elementAt(lastIndex);
        mainPanel.remove(nixedButton);
 //       buttonList.removeElementAt(lastIndex);
        mainPanel.revalidate(); // Make the button disappear.
        mainPanel.repaint(); // Make the button disappear.
      } catch (ArrayIndexOutOfBoundsException exc) {
      }
    }*/ else if (CLEAR.equals(command)) {
        remove(displayResource);
        remove(displayGateway);
        remove(scrollPaneResource);
        remove(scrollPaneGateway);
        remove(clearButton);
        hello();
        inputArea.setText("");
        displayGateway.setText("");
        displayResource.setText("");
      mainPanel.revalidate(); // Make the button disappear.
      mainPanel.repaint(); // Make the button disappear.
    }
  }
  /**
   * Create the GUI and show it. For thread safety, this method should be
   * invoked from the event-dispatching thread.
   */
  private static void createAndShowGUI() {
      hello();
  }
  public static void hello () {
        // Create and set up the window.
        JFrame frame = new JFrame("ContainerEventDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        // Create and set up the content pane.
        JComponent newContentPane = new ContainerEventDemo();
        newContentPane.setOpaque(true); // content panes must be opaque
        frame.setContentPane(newContentPane);
        // Display the window.
        frame.pack();
        frame.setVisible(true);

  }

  public static void main(String[] args) {
    // Schedule a job for the event-dispatching thread:
    // creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        createAndShowGUI();
      }
    });
  }
}**

Thanks for any help.

Answer 1

The "problem" is mainPanel. You don't seem to be adding anything to it, but neither are you removing it when you "switch" views, so it remains and takes up space.

I'm "assuming" you're using it as a filler of some kind, but you seem to have forget that it's there.

My recommendation is to stop "manually" manipulating the UI like this, seperate your "views" into individual classes, so that they can have a focused layout and managed in isolation from each other and use a CardLayout to switch between them

Updated

I can foresee a bunch of statements about how the UI was established and not understanding why this happening this way etc...

Basically, you're establishing the layout of the core UI using c.gridwidth = GridBagConstraints.REMAINDER. Okay this is fine.

But, when you remove all the other components, this pushes mainPanel to the top, combined with c.weighty = 1.0, makes it want to occupy the remaining available space left over by the other components.

This is basically you core problem. So, break down the view's into separate classes and manage them as a "whole", it will solve most of the key problems immediately