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Java component positioning on GridBagLayout

I am trying to position components on JPanel using GridBagLayout but the output I am getting is completely off from what I expect. Hope to get some clarity with brilliant-minded ppl in stackoverflow:).
Below I have provided a piece of code and screentshot of the program. My questions are:
Why the JLabel Choose measure system to convert is not on Y-axis = 1? As to my knowledge, c.gridy=1 is one pixel downward, but the label is stuck on the top leaving no space from the Frame title. And also, why is it positioned so weird, i.e., not really in the center, nor in the start?
Why is there such a big space between ComboBoxes From... and To..., but there is no space between ComboBox To... and TextField Enter value here...?
Here is the code:
JPanel container = new JPanel();
container.setLayout(new GridBagLayout());
getContentPane().add(container, BorderLayout.NORTH);
TitledBorder outputCenter;
GridBagConstraints c = new GridBagConstraints();
label = new JLabel("Choose measure system to convert");
label.setFont(new Font("Times New Roman", Font.PLAIN, 20));
c.gridx = 0;
c.gridy = 1;
container.add(label, c);
fromList = new JComboBox<String>(convertFrom);
c.gridx = 0;
c.gridy = 2;
container.add(fromList, c);
toList = new JComboBox<String>(convertTo);
c.gridx = 1;
c.gridy = 2;
container.add(toList, c);
//Field where user enters the value to be converted
input = new JTextField("Enter value here...");
input.setPreferredSize(new Dimension(150,30));;
input.setEditable(true);
input.setBackground(Color.WHITE);
input.setBorder(BorderFactory.createLineBorder(Color.BLACK));
input.addMouseListener(new MouseAdapter(){
public void mouseClicked(MouseEvent e){
input.setText("");}});
c.gridx = 2;
c.gridy = 2;
container.add(input, c);
And here is the screentshot:
EDIT: If I change the code from:
label = new JLabel("Choose measure system to convert");
label.setFont(new Font("Times New Roman", Font.PLAIN, 20));
c.gridx = 0;
c.gridy = 1;
container.add(label, c);
label = new JLabel("Choose measure system to convert");
label.setFont(new Font("Times New Roman", Font.PLAIN, 20));
c.gridx = 1; // changed this line
c.gridy = 1;
container.add(label, c);
The outcome is like this:
This is very confusing me as why changing the position of one component effects everything?

GridBagConstraints sets up the frame into effectively a grid. The width and height of the cells in the grid are determined by the size of the data in the cell by default unless otherwise specified. So if you want to add some space in-between cells I suggest ipadx and ipady. You can also utilize anchor for adjusting your data in the cell. I also suggest weightx and weighty for adjusting the actual cell size.
So imagine something like this as your current set up:
EDIT: Example of what your new GBC looks like. The numbers are (gridx,gridy)

Why the JLabel Choose measure system to convert is not on Y-axis = 1? As to my knowledge, c.gridy=1 is one pixel downward
You're confusing yourself, c.gridy = 1 is not positioning it 1 pixel downward but rather on the next row, but as there's no previous row, then it takes the first row. For reference see: GridBagConstraints#gridy which says the following:
Specifies the cell at the top of the component's display area, where the topmost cell has gridy=0. The value RELATIVE specifies that the component be placed just below the component that was added to the container just before this component was added.
Next question:
And also, why is it positioned so weird, i.e., not really in the center, nor in the start?
It is centered in its own cell, if you want to center it on the JFrame, then you might need to create it on its own gridx = 1 and the rest of components on the other ones (0 and 2) or make it span 2 or more columns based on you want it to look like...
Why is there such a big space between ComboBoxes From... and To..., but there is no space between ComboBox To... and TextField Enter value here...?
It is because your program is giving it all the extra space because of the large text on the first cell...
You can have something like this:
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class GridBagLayoutExample {
private JFrame frame;
private JPanel pane;
private JLabel label;
private JTextField field;
private JComboBox<String> box1;
private JComboBox<String> box2;
private GridBagConstraints gbc;
public static void main(String[] args) {
SwingUtilities.invokeLater(new GridBagLayoutExample()::createAndShowGui);
}
private void createAndShowGui() {
frame = new JFrame(getClass().getSimpleName());
pane = new JPanel();
pane.setLayout(new GridBagLayout());
gbc = new GridBagConstraints();
label = new JLabel("Choose measure system to convert");
box1 = new JComboBox<>(new String[] {"From..."});
box2 = new JComboBox<>(new String[] {"To..."});
field = new JTextField(10);
gbc.insets = new Insets(5, 5, 5, 5); //We add extra space at top, left, bottom, right of each component
gbc.gridx = 0;
gbc.gridy = 0;
gbc.gridwidth = 3; //We make our text to span 3 cells
pane.add(label, gbc);
gbc.gridy = 1;
gbc.gridwidth = 1; //We return the spanning to 1 single cell
pane.add(box1, gbc);
gbc.gridx = 1;
pane.add(box2, gbc);
gbc.gridx = 2;
pane.add(field, gbc);
frame.add(pane);
frame.pack();
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}
Which produces the following output:

Difficulties in aligning ScrollPane in top-left corner

The question is, how do I align JScrollPane in resizeble JPane so that it aligns to the top-left corner instead of a center?
That feels like obvious task, yet I spent hours trying out all the different layouts and properties.
The frustration can be expressed, as there are only two options I could produce:
Use the layout which respects children's maximum preferred size, FlowLayout as example. Side effect - ScrollPane starts behaving as if it was plain Panel:
Use stretchable layout, for instance BorderLayout and place the element into BorderLayout.CENTER (BorderLayout.PAGE_START leads to 1.). I lose control on the location of Panel, and it in the center:
When window is small, scroll works as expected though:
Is it possible to have both of the two worlds: have JScrollPane not stretch beyound maximum preferred size, yet not lose the Scroll?
In case someone needs the source code:
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTabbedPane;
public class MainPanelTest extends JFrame {
public static void main(String[] args) {
new MainPanelTest().setVisible(true);
}
public MainPanelTest() {
super();
this.setLayout(new BorderLayout());
setupGUI();
}
private void setupGUI() {
JTabbedPane tabbedPane = new JTabbedPane();
tabbedPane.setTabLayoutPolicy(JTabbedPane.SCROLL_TAB_LAYOUT);
this.add(tabbedPane, BorderLayout.CENTER);
JComponent filesPanel = setupFilesPanel();
tabbedPane.addTab("Files", filesPanel);
JPanel secondPanel = new JPanel();
tabbedPane.addTab("Placeholder", secondPanel);
}
private JComponent setupFilesPanel() {
JPanel filesPanel = new JPanel();
filesPanel.setLayout(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();
c.anchor = GridBagConstraints.NORTHWEST;
for(int i=0; i<15; i++) {
c.gridy = i;
filesPanel.add(new JLabel("Test row " + i), c);
}
JScrollPane scrollFilesPane = new JScrollPane(filesPanel);
scrollFilesPane.setMaximumSize(scrollFilesPane.getPreferredSize());
return scrollFilesPane;
}
}

The GridBagLayout divides the space into logical cells in which the components live. The anchor is only relevant if the logical cell is bigger than its component. This may happen if components within the same row/column demand a bigger size or if there is extra space and the associated weightx or weighty value is not zero. Since your desired behavior is about the extra space, you have to set the weight values accordingly. The weightx will be non-zero for the sole column but the weighty will be non-zero for the last row only to take up the entire space below it:
GridBagLayout gridBagLayout = new GridBagLayout();
JPanel filesPanel = new JPanel(gridBagLayout);
GridBagConstraints c = new GridBagConstraints();
c.gridx = GridBagConstraints.REMAINDER;
c.anchor = GridBagConstraints.NORTHWEST;
c.weightx = 1; // for the column
for(int i=0; i<15; i++)
filesPanel.add(new JLabel("Test row " + i), c);
// now change the last row:
c.weighty = 1;
gridBagLayout.setConstraints(
filesPanel.getComponent(filesPanel.getComponentCount()-1), c);
Alternatively you can leave the cells unmodified but manipulate the entire layout by adding an empty extra row and column consuming the additional space which will effectively move the original rows and columns to the upper left corner:
// add all visible components which should not grow
GridBagLayout gridBagLayout = new GridBagLayout();
JPanel filesPanel = new JPanel(gridBagLayout);
GridBagConstraints c = new GridBagConstraints();
c.gridx = GridBagConstraints.REMAINDER;
for(int i=0; i<15; i++)
filesPanel.add(new JLabel("Test row " + i), c);
// add an extra row consuming vertical extra space
int nRows=filesPanel.getComponentCount();
gridBagLayout.rowHeights=new int[nRows+1];
gridBagLayout.rowWeights=new double[nRows+1];
gridBagLayout.rowWeights[nRows]=1;
// add an extra column consuming extra horizontal space
gridBagLayout.columnWidths=new int[] { 0, 0 };
gridBagLayout.columnWeights=new double[] { 0, 1 };

See if this is what you are trying to achieve:
private JComponent setupFilesPanel() {
JPanel filesPanel = new JPanel();
filesPanel.setLayout(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();
c.anchor = GridBagConstraints.NORTHWEST;
for(int i=0; i<15; i++) {
c.gridy = i;
filesPanel.add(new JLabel("Test row " + i), c);
}
// ---- Add this
JPanel newPanel = new JPanel(new GridBagLayout());
c.weightx = 1;
c.weighty = 1;
newPanel.setBackground(Color.yellow);
newPanel.add(filesPanel, c);
// ----
// ---- change the panel you pass to JScrollPanel constructor:
JScrollPane scrollFilesPane = new JScrollPane(newPanel); // <--------- newPanel
scrollFilesPane.setMaximumSize(scrollFilesPane.getPreferredSize());
return scrollFilesPane;
}
The changes are commented.

GridBagLayout and Resizing

getting a bit confused with GridBagLayout.
import javax.swing.JLabel;
import javax.swing.JFrame;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import java.awt.*;
import java.awt.event.*;
public class MihatteFrame extends JFrame {
private JTextArea area;
private JTextField textField;
private Button b;
final static boolean shouldFill = true;
public MihatteFrame() {
setTitle("見張ってしながら...");
setSize(500,200);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setLocationRelativeTo(null);
setLayout(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();
if (shouldFill) {
c.fill = GridBagConstraints.HORIZONTAL;
}
area = new JTextArea(5, 15);
area.setEditable(false);
area.setCursor(null);
area.setOpaque(false);
area.setFocusable(false);
area.setLineWrap(true);
area.setWrapStyleWord(true);
c.fill = GridBagConstraints.HORIZONTAL;
c.weightx = 0;
c.gridx = 0;
c.gridy = 0;
c.anchor = GridBagConstraints.WEST;
this.add(area, c);
textField = new JTextField(20);
c.fill = GridBagConstraints.HORIZONTAL;
c.weightx = 1;
c.gridx = 2;
c.gridy = 0;
c.anchor = GridBagConstraints.CENTER;
this.add(textField);
//textField.addActionListener(this);
b = new Button("Proceed");
c.fill = GridBagConstraints.HORIZONTAL;
c.weightx = 0;
c.gridx = 2;
c.gridy = 0;
this.add(b);
setVisible(true);
}
public void displayText(String text) {
area.setText(text);
//textField.setText(text)
}
}
I understand the basics and its working well, it`s sorting out the resizing (specifically downsizing) issue.
When the text areas weight is 0 and the text fields weight is 1, there is no problem with resizing, but the text area is in the centre and not right up against the left-hand side, despite the anchoring.
When the text areas weight is anything above 0 and the text fields weight correlates (eg. 0.2/0.8), everything looks snug as a bug, and upsizing is fine, but downsizing, the text field is reduced to 1 character wide.
I dont mind the text area resizing with the frame, but I want it to return to its original size when the frame is made smaller, not shove the textfield against the proceed button.
I have read that I may need to put this in a JPanel border layout - am not sure what this would look like in code, so if anyone could tell me what goes where if that is the case, would be grateful.
So questions:
Is there a way to make the text area stay anchored to the West AND
not have the textfield reduced to a small size when resized?
Why are my anchors not working?
Do I need to put the text area in a JPanel with relation to another layout, and if so, where does the code go?
Why does everyone fear GridBagLayout? The amount of "I avoid this at all costs" I`ve seen...
Thank you!
(Ps. am halfway through implementing actionlistener, so if it looks half-complete, that`s why).

Use ipadx for the JTextField. I would suggest also to place the JTextArea in a JScrollPane.
You use c.gridx = 2 twice for the JTextField and JButton.
It's better to post SSCCE to let us check what's wrong.

Java : gridbaglayout confusion

this is my first question on here, so please forgive me when i am breaking any rules, or not using the right format
I am creating a simple form in java swing which consists of 1 JLabel, 1 JTextField, and 1 Button
|---------------------------|
| |
| JLabel |
| |
|---------------------------|
| JTextField | Button |
|---------------------------|
The Button should be in the bottom-right corner, the JTextField left of it, the JLabel on the top, spanning both columns
I want the Button to be a fixed size, the JTextField a fixed height, but using the full width (except for what is in use by the Button), and the JLabel using all other space (with and height)
I am not even sure if i should use a GridBagLayout or another Layout ?
This is probably a very easy question, but got me puzzled for quite some time (too many options with the GridBarLayout i guess)

First, set the layout of your panel to GridBagLayout.
Then, create a GridBagConstraints object and set the fill to GridBagConstraints.BOTH.
For the JLabel, set the following properties on the constraints object: gridx = 0, gridy = 0, gridwidth = 2, gridheight = 2, weightx = 1, weighty = 1.
For the JTextField, set the following properties on the constraints object: gridx = 0, gridy = 1, gridwidth = 1, gridheight = 1, weightx = 1, weighty = 0.
For the JButton, set the following properties on the constraints object: gridx = 1, gridy = 1, gridwidth = 1, gridheight = 1, weightx = 0, weighty = 0.

Class BorderLayout is easy to use, less powerful than GridBagLayout.
But when thing are simple, solution have to be the same.
panel.add( label, BorderLayout.CENTER );
JPanel south = new JPanel();
south.add( textfield );
south.add( button );
button.setPreferredSize( x, y );
panel.add( south, BorderLayout.SOUTH );

OK here is a demo code that should get you going:
import java.awt.Color;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class TestGridBagLayout {
protected void initUI() {
JFrame frame = new JFrame(TestGridBagLayout.class.getSimpleName());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JButton button = new JButton("A button");
JTextField textField = new JTextField();
JLabel label = new JLabel("A cool long nice label that will stretch.");
label.setHorizontalAlignment(JLabel.CENTER);
label.setBorder(BorderFactory.createLineBorder(Color.GREEN));
JPanel panel = new JPanel(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
gbc.fill = GridBagConstraints.BOTH;// Fill the "cell" in both direction
gbc.weightx = 1.0;// Allocate extra-width to the label
gbc.weighty = 1.0;// Allocate extra-height to the label
gbc.gridwidth = GridBagConstraints.REMAINDER;// The label takes all the available width of the "row"
panel.add(label, gbc);
gbc.weighty = 0; // Don't stretch TF vertically
gbc.fill = GridBagConstraints.HORIZONTAL; // Fill horizontally
gbc.gridwidth = GridBagConstraints.RELATIVE;
panel.add(textField, gbc);
gbc.weightx = 0; // No extra horizontal space is given to the button
gbc.fill = GridBagConstraints.NONE; // No fill for the button
panel.add(button, gbc);
frame.add(panel);
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new TestGridBagLayout().initUI();
}
});
}
}

I don't know this is a common thing to do, but below is code which is working (mainly code from Dan and Guillaume)
//show stuff
setLayout(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();
//show label
c.fill = GridBagConstraints.BOTH; // Fill the "cell" in both direction
c.weightx = 1.0; // Allocate extra-width to the label
c.weighty = 1.0; // Allocate extra-height to the label
c.gridwidth = GridBagConstraints.REMAINDER; // The label takes all the available width of the "row"
add(mlblShow,c);
//show cmd txt
c.weighty = 0; // Don't stretch TF vertically
c.fill = GridBagConstraints.BOTH; // Fill horizontally and vertically
c.gridwidth = GridBagConstraints.RELATIVE;
add(mtxtCmd,c);
//show send button
c.weightx = 0; // No extra horizontal space is given to the button
c.fill = GridBagConstraints.NONE; // No fill for the button
add(cmdSend,c);

GridBagLayout not showing JTextArea, and showing panel in center

In the following code, when I add the JTextArea to the main panel, it doesn't show up. When I add the controlPanel, it shows up in the center, not the edge. I'm new with GridBagLayout, so I'm assuming I'm missing something simple.
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSpinner;
import javax.swing.JTextArea;
public class Main {
public static void main(String[] args) {
new Main();
}
public Main() {
JFrame frame = new JFrame();
JPanel mainPanel = new JPanel();
JPanel controlPanel = new JPanel();
mainPanel.setLayout(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();
controlPanel.add(new JButton("Play"));
controlPanel.add(new JButton("Pause"));
controlPanel.add(new JSpinner());
JTextArea textArea = new JTextArea();
c.gridx = 0;
c.gridy = 0;
c.gridheight = 3;
c.gridwidth = 3;
mainPanel.add(textArea, c);
// mainPanel.add(controlPanel, c);
frame.add(mainPanel);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(700, 700);
frame.setLocation(250, 100);
frame.setVisible(true);
}
}
EDIT: This is how the constraints look after your suggestions. The textArea still does not show up.
c.gridx = 0;
c.gridy = 0;
// c.gridheight = 3;
// c.gridwidth = 3;
c.weightx = 1.0;
c.weighty = 1.0;
c.anchor = GridBagConstraints.NORTHWEST;
mainPanel.add(textArea, c);
// mainPanel.add(controlPanel, c);
frame.add(mainPanel);

Don't forget weights and anchors:
c.weightx = 1.0;
c.weighty = 1.0;
c.anchor = GridBagConstraints.NORTHWEST;
Edit:
Example of adding row and column values to the JTextArea:
controlPanel.add(new JButton("Play"));
controlPanel.add(new JButton("Pause"));
controlPanel.add(new JSpinner());
JTextArea textArea = new JTextArea(20, 40);
c.gridx = 0;
c.gridy = 0;
c.gridheight = 3;
c.gridwidth = 3;
c.weightx = 1.0;
c.weighty = 1.0;
c.anchor = GridBagConstraints.NORTHWEST;
mainPanel.add(new JScrollPane(textArea), c);

My totally serious answer would be to not use GridBagLayout. Leave GridBagLayout for the GUI form builders.
If you want to build GUI's by hand (I recommend building them by hand and avoiding form builders, BTW) then generally BorderLayout with nested panels using BoxLayouts are really your best bet.