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How to make components evenly share JPanel container vertical area with GridBagLayout layout on resizing?

The problem:
JPanel with GridBagLayout contains two JScrollPane components, the top one contains JTextArea, the bottom one contains JTable. I expect this set up to make the components fluidly fill the container JPanel and evenly share the vertical area of it on resizing. What actually happens is that the top JScrollPane component shrinks vertically on resizing giving more vertical area to the bottom JScrollPane component to invade; this happens at some sizes, I don not know if they are random.
Important notes:
I already applied GridBagConstraints#weighty = 0.5; to both components, which is supposed to do the job.
I noticed that the problem is because of the presence of the JTextArea, in that if I switch locations; make the JScrollPane/JTextArea on the bottom side and JScrollPane/JTable on the top side; the bottom component JScrollPane/JTextArea shrinks vertically giving more vertical area to the top component JScrollPane/JTable to invade.
I know this exact case can be solved simply using GridLayout(2,1) instead of GridBagLayout (or may be other solutions), however I am fan of GridBagLayout and I want to use most of it. Also if I want to add three components instead of two and I want to make them share the vertical area by percentage for example (%25, %25, 50%) I can use GridBagConstraints#weighty = (0.25, 0.25, 0.5) which is easily applicable with GridBagLayout.
So, in this case how to make components evenly share the vertical area of JPanel container with GridBagLayout on resizing?. Or, in other words; how to enforce components to respect GridBagConstraints#weighty = 0.5; setting on resizing which is applied to both?
Code in SSCCE format:
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.JTextArea;
import javax.swing.table.DefaultTableModel;
public class GridBagFluidFill {
private static JPanel createFormPanel() {
JPanel containerPanel = new JPanel(new GridBagLayout());
containerPanel.setPreferredSize(new Dimension(350, 200));
JScrollPane scrollableTextArea;
JScrollPane scrollableTable;
JTextArea textArea = new JTextArea();
scrollableTextArea = new JScrollPane(textArea);
DefaultTableModel model = new DefaultTableModel(new String[]{"Column1", "Column2", "Column3"}, 0);
JTable table = new JTable(model);
scrollableTable = new JScrollPane(table);
GridBagConstraints c = new GridBagConstraints();
c.gridy = 0;
c.weightx = 1.0;
// I expect this to reserve 50% of the height all time.
c.weighty = 0.5;
c.fill = GridBagConstraints.BOTH;
c.anchor = GridBagConstraints.PAGE_START;
containerPanel.add(scrollableTextArea, c);
c = new GridBagConstraints();
c.gridy = 1;
c.weightx = 1.0;
// I expect this to reserve 50% of the height all time.
c.weighty = 0.5;
c.fill = GridBagConstraints.BOTH;
c.anchor = GridBagConstraints.PAGE_END;
containerPanel.add(scrollableTable, c);
return containerPanel;
}
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(() -> {
JPanel formPanel = createFormPanel();
JFrame frame = new JFrame("GridBagFluidFill");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(formPanel);
frame.pack();
frame.setVisible(true);
});
}
}

GridBagLayout is complex, and while its documentation does describe all of its functionality, some of it is easy to misinterpret.
I already applied GridBagConstraints#weighty = 0.5; to both components, which is supposed to do the job.
That is not what weightx and weighty do.
Equal weightx and weighty values do not coerce components into having the same width or height. The weight values determine the distribution of extra space when a container is larger than the preferred sizes of each component.
Here is a program which demonstrates this:
import java.awt.EventQueue;
import java.awt.GridBagLayout;
import java.awt.GridBagConstraints;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JPanel;
import javax.swing.JFrame;
public class GridBagEqualWeightsDemo {
static void showWindow() {
// Source: https://www.gutenberg.org/files/98/98-h/98-h.htm
String text =
"It was the best of times, it was the worst of times, it was"
+ " the age of wisdom, it was the age of foolishness, it was the"
+ " epoch of belief, it was the epoch of incredulity, it was the"
+ " season of Light, it was the season of Darkness, it was the"
+ " spring of hope, it was the winter of despair, we had everything"
+ " before us, we had nothing before us, we were all going direct"
+ " to Heaven, we were all going direct the other way—in short,"
+ " the period was so far like the present period, that some of its"
+ " noisiest authorities insisted on its being received, for good"
+ " or for evil, in the superlative degree of comparison only.";
JTextArea topArea = new JTextArea(text, 4, 20);
topArea.setLineWrap(true);
topArea.setWrapStyleWord(true);
JTextArea bottomArea = new JTextArea(text, 8, 20);
bottomArea.setLineWrap(true);
bottomArea.setWrapStyleWord(true);
JScrollPane top = new JScrollPane(topArea);
JScrollPane bottom = new JScrollPane(bottomArea);
top.setMinimumSize(top.getPreferredSize());
bottom.setMinimumSize(bottom.getPreferredSize());
JPanel panel = new JPanel(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
gbc.fill = GridBagConstraints.BOTH;
gbc.gridwidth = GridBagConstraints.REMAINDER;
gbc.weightx = 1;
gbc.weighty = 0.5;
panel.add(top, gbc);
panel.add(bottom, gbc);
JFrame frame = new JFrame("GridBagConstraints Equal Weights");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(panel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
EventQueue.invokeLater(() -> showWindow());
}
}
As you can see, the two components start out with different preferred heights, so GridBagLayout will never give them the same height. As you make the window taller, the components’ respective heights look more similar due to the smaller relative difference, but they are never the same.
GridBagLayout only uses the weighty to determine how to distribute the extra space—that is, the container height which exceeds each component’s (different) preferred height. If the panel is 50 pixels higher than the preferred height, as computed based on each child component’s preferred size, then equal weighty values means each component will be laid out with 25 pixels added to its respective preferred height.
If you want to force two components which may have different preferred sizes to always have the same width and/or height, GridBagLayout is the wrong tool for the job. As you have mentioned, GridLayout is well suited to this. SpringLayout can also do this, though its usage is complex.
You are free (and encouraged!) to use multiple panels inside each other with different layouts.

I already applied GridBagConstraints#weighty = 0.5; to both components, which is supposed to do the job.
The weighty constraint is used to tell the GridBagLayout how to allocate "extra" (and apparently less) space.
That is, each component is first allocated its preferred space. Then if there is extra (or apparently less) space available, that constraint is used.
If you add debug code to display the preferred sizes of each scroll pane you will get:
java.awt.Dimension[width=223,height=19] // text area
java.awt.Dimension[width=453,height=403] // table
So the issue is with this statement:
containerPanel.setPreferredSize(new Dimension(350, 200));
You are forcing the components to be smaller than their preferred size. So it appears the GridBagLayout is allocating 50% to each.
I was wondering why JTextArea shrinks without a good reason
As the height of the frame grows each component is allocated 50% until the point at which the frame is large enough to display each component at its preferred size. This is why the text area shrinks and the table jumps.
As you increase the height from there extra space is allocated at 50/50 as expected.
If you uncomment the setPreferredSize() statement you will see the natural layout and the reason for the jumping becomes clear.
I want to make them share the vertical area by percentage for example (%25, %25, 50%)
If you want allocations like that then check out Relative Layout which was designed for this purpose.

Using WrapLayout with multiple adjacent JPanels is causing Panel sizing issues

I have 3 adjacent JPanels that each use WrapLayout to display a variable number of 1x16 grids.
It works great for the panel which contains the most 1x16 grids, however, the other two panels' dimensions seem to be determined by the panel that contains the most 1x16 grids. If, for example, panels 1 and 2 have only one 1x16 grid respectively, but panel 3 has ten 1x16 grids spread across two rows, then panel 1 and 2 both have a 1x16 grid-sized empty space beneath their respective 1x16 grids.
I basically want to get each panel's resizing to operate independently of the other panels. I've looked through camickr's src code for WrapLayout and can't quite work out what I should change to get the desired result.
In terms of code, it's tricky to know how to include a succinct and instructive section, as the code is quite spread out and I'm not sure what part is causing this issue. I'm just setting the panels' layout as a left-justified WrapLayout.
I've included an image below which might provide some context. The image shows part of two of the three JPanels (coloured cyan) and the accompanying title JLabel for one of those JPanels (coloured green). The 1x16 grids on each panel are managed using camickr's WrapLayout. All three cyan JPanels are contained within a larger display JPanel that has then been packed into a JScrollPane (hence the grey scroller to the right of the image).
Any help would be really appreciated.
Here's another image I created that shows the issue a little more clearly. The third panel in the image wraps to a new row to display all the 1x16 grids that it contains, and in so doing, doubles the height of the other two panels, despite them not needing to resize.
Here's how I want the GUI to display:

Judging from the desired behaviour vs the actual behaviour images, the problem lies in the LayoutManager you use to lay out the 3 panels into their parent panel/frame (which I am guessing is a GridLayout because the 3 panels have equally distributed sizes). If so, use some other LayoutManager, such as a vertical BoxLayout.
An example code and tutorial can be found in the Oracle's corresponding one (the actual code sample of which, can be found in this link with fancy code coloring, or here as plain text).

I created the following GUI.
I created a JFrame. I created one main JPanel to place inside the JFrame. The main JPanel uses a GridBaglayout to separate three cyan JPanels.
Each cyan JPanel calculates a preferred size based on the number of black JPanels placed in the cyan JPanel. Change the boxesPerRow value to get a different number of boxes per row.
Each black JPanel is created with a preferred size of 20 x 80 pixels;
Here's the complete runnable code. A minimal reproducible example, in other words.
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class BoxesGUI implements Runnable {
public static void main(String[] args) {
SwingUtilities.invokeLater(new BoxesGUI());
}
#Override
public void run() {
JFrame frame = new JFrame("Boxes");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(createMainPanel(), BorderLayout.CENTER);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
private JPanel createMainPanel() {
JPanel panel = new JPanel(new GridBagLayout());
panel.setBackground(Color.BLACK);
panel.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
GridBagConstraints gbc = new GridBagConstraints();
gbc.anchor = GridBagConstraints.LINE_START;
gbc.fill = GridBagConstraints.HORIZONTAL;
gbc.insets = new Insets(5, 5, 5, 5);
gbc.weightx = 1.0;
gbc.gridx = 0;
gbc.gridy = 0;
panel.add(createCyanPanel(1), gbc);
gbc.gridy++;
panel.add(createCyanPanel(1), gbc);
gbc.gridy++;
panel.add(createCyanPanel(20), gbc);
return panel;
}
private JPanel createCyanPanel(int count) {
JPanel panel = new JPanel(new FlowLayout(FlowLayout.LEADING, 5, 5));
panel.setBackground(Color.CYAN);
JPanel dummyPanel = createBlackPanel();
Dimension d = dummyPanel.getPreferredSize();
int boxesPerRow = 8;
int width = (d.width + 5) * boxesPerRow + 5;
int height = ((count + boxesPerRow - 1) / boxesPerRow) * (d.height + 5) + 5;
panel.setPreferredSize(new Dimension(width, height));
for (int i = 0; i < count; i++) {
panel.add(createBlackPanel());
}
return panel;
}
private JPanel createBlackPanel() {
JPanel panel = new JPanel();
panel.setBackground(Color.BLACK);
panel.setPreferredSize(new Dimension(20, 80));
return panel;
}
}

How to fill Cells of GridbagLayout with the controls in Swing?

I need to design a swing GUI which has a JFrame with a Menu on top and another main panel having three more panels in center and a separate panel in the bottom of the panel. The required design of the UI is as below
But when I run my swing application I get the output like this (all the panels are packed in the center of the window)
Below is my code
import java.awt.*;
import javax.swing.*;
public class FrontEndView {
private JFrame mainFrame;
private JPanel mainPanel,subPanelUp,subPanelDown,panelLeft,panelRight,panelCenter,panelDown;
private JScrollPane scrollPane;
private JList logViewList;
private JPanel panel1;
public FrontEndView(){
this.prepareGUI();
}
public void prepareGUI(){
mainFrame=new JFrame("GUI");
Toolkit tk = Toolkit.getDefaultToolkit();
int xSize = ((int) tk.getScreenSize().getWidth());
int ySize = ((int) tk.getScreenSize().getHeight());
mainFrame.setSize(xSize,ySize);
mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
mainFrame.setResizable(true);
mainFrame.setLayout(new BorderLayout());
mainPanel=new JPanel();
mainPanel.setLayout(new GridBagLayout());
mainPanel.setComponentOrientation(ComponentOrientation.LEFT_TO_RIGHT);
GridBagConstraints gridbagConstMain = new GridBagConstraints();
GridBagConstraints gridbagConstSub = new GridBagConstraints();
subPanelUp=new JPanel();
subPanelUp.setLayout(new GridBagLayout());
subPanelUp.setComponentOrientation(ComponentOrientation.LEFT_TO_RIGHT);
panelLeft=new JPanel();
panelLeft.setBorder(BorderFactory.createTitledBorder("Message Defs"));
gridbagConstSub.fill = GridBagConstraints.HORIZONTAL;
gridbagConstSub.weightx = 0.5;
gridbagConstSub.gridx = 0;
gridbagConstSub.gridy = 0;
subPanelUp.add(panelLeft, gridbagConstSub);
panelCenter=new JPanel();
panelCenter.setBorder(BorderFactory.createTitledBorder("Main Workspace"));
gridbagConstSub.fill = GridBagConstraints.HORIZONTAL;
gridbagConstSub.weightx = 0.5;
gridbagConstSub.gridx = 1;
gridbagConstSub.gridy = 0;
subPanelUp.add(panelCenter, gridbagConstSub);
panelRight=new JPanel();
panelRight.setBorder(BorderFactory.createTitledBorder("Script Viewer"));
gridbagConstSub.fill = GridBagConstraints.HORIZONTAL;
gridbagConstSub.weightx = 0.5;
gridbagConstSub.gridx = 2;
gridbagConstSub.gridy = 0;
subPanelUp.add(panelRight, gridbagConstSub);
mainPanel.add(subPanelUp,gridbagConstMain);
subPanelDown=new JPanel();
subPanelDown.setLayout(new BorderLayout());
panelDown=new JPanel();
panelDown.setBorder(BorderFactory.createTitledBorder("Log View"));
logViewList= new JList();
panelDown.add(logViewList);
gridbagConstSub.fill = GridBagConstraints.HORIZONTAL;
//gridbagConst.ipady=20;
//gridbagConst.weightx = 0.0;
gridbagConstSub.gridwidth = 5;
gridbagConstSub.gridx = 0;
gridbagConstSub.gridy = 0;
subPanelDown.add(panelDown,BorderLayout.PAGE_END);
mainPanel.add(subPanelDown, gridbagConstSub);
scrollPane=new JScrollPane(mainPanel,ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED,ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED);
mainFrame.add(scrollPane);
mainFrame.setVisible(true);
}
public static void main(String[] args){
FrontEndView frontEnd = new FrontEndView();
}
}
I want to fill the GridBagLayout's cells with the relevant panel/control it holds as shown in the design and also each panel should have its controls filled inside (I need to add a JList inside the panelDown whose size should be the size of the panelDown JPanel).Simply I don't need any extra space visible in my JFrame. Please guide me on what is missing in my code.

I would suggest you can use nested panels with different layout managers to solve the problem.
The default layout of a frame is a BorderLayout.
So you could create a panel and add it to the PAGE_END so it displays the entire width at the bottom.
Then you can create another panel that uses a GridLayout. You can then add 3 child panels to this panel and each panel can use its own layout. Then you add this panel to the CENTER of the frame. As the frame size changes the extra spaces will be allocated to the CENTER so the panels will dynamically grow.
Edit:
Too many panels for me to take the time to understand what is happening
I was suggesting a structure like this:
frame (which by default uses a BorderLayout)
--- CENTER
panel using GrigBagLayout
childPanel1
childPanel2
childPanel3
---- PAGE_END
JScrollPane containing the JList
When you create the JList the basic code would be:
JList list = new JList(...);
list.setVisibleRowCount(5);
JScrollPane scrollPane = new JScrollPane( list );
There is no need to create a panel just to add the list to another panel. The point of setting the visible row count is to give the JList a fixed height. Scrollbars will then appear in the scroll pane as needed.
Now that the PAGE_END has a fixed height component all the reset of the space will go to the component that you add to the CENTER of the frame.
all the panels are packed in the center of the window)
The panels are displayed at their preferred sizes when you use the GridBagLayout. If the total size of all the panels is less than the size of the scrollpane then they will be in the center. If you want the panels to fill the space available, then I believe you need to use the weightx/y constraints. Read the section from the Swing tutorial on How to Use GridBagLayout which describes all the constraints.
That is why I suggested a GridLayout instead. It will make all the panels the same size and will fill the viewport of the scroll pane without playing with constraints.
mainFrame.add(menubar,BorderLayout.NORTH);
That is not how you add a menubar to the frame.
You should be using:
mainFrame.setJMenuBar(menuBar);
You were told this in your last question. Why did you not listen to the advice??? Why should we take the time to help when you don't pay attention to what is suggested.

Based on your instructions I changed my design in a way all of the outer panels are used with Border Layout and the inner most ones with more controls were used with Grid, GridBag and FlowLayouts based on the requirement. In that way the entire design could be done nicely.
Also if a particular panel within a cell of a layout needs to be expanded, I used the setPreferredSize(new Dimension(int,int)) whenever required.

How to control the size of the panels

I'm learning swing gui and I get this result when I use the following code:-
The code I use :-
private void initUI() {
JTextArea visualize=new JTextArea();
visualize.setEditable(false);
//DEFINE BUTTONS....
JButton[] buttons1={addition,subtraction,division,multiplication};
JButton [] buttons2={expr,date,conversion};
JPanel numerical=new JPanel(new FlowLayout());
numerical.setPreferredSize(new Dimension(350, 50));
for(int i=0;i<buttons1.length;i++){
numerical.add(buttons1[i]);
}
numerical.setBorder(new TitledBorder("Numerical Operations"));
JPanel nonnum=new JPanel(new FlowLayout());
nonnum.setPreferredSize(new Dimension(500, 50));
for(int i=0;i<buttons2.length;i++){
nonnum.add(buttons2[i]);
}
nonnum.setBorder(new TitledBorder("Non-numerical Operations"));
JPanel operations = new JPanel(new BorderLayout(2,2));
operations.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
operations.setSize(800, 100);
operations.add(numerical,BorderLayout.WEST);
operations.add(nonnum,BorderLayout.EAST);
JTable sheet = new JTable(10,5);
add(visualize, BorderLayout.NORTH);
add(sheet,BorderLayout.SOUTH);
add(operations,BorderLayout.CENTER);
pack();
setSize(1000, 700);
setTitle("Spreadsheet Application");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLocationRelativeTo(null);
}
But what I really want is this:-
My questions :-
Why is the operations panel too long?
How can I change it's height?
Doesn't "operations.setSize(..)" work?

Try using GroupLayout.
I'm also new to swing gui and had similar problems - GroupLayout saved the day
JPanel complete=new JPanel();
GroupLayout gl=new GroupLayout(complete);
complete.setLayout(gl);
gl.setAutoCreateContainerGaps(true);
gl.setHorizontalGroup(gl.createParallelGroup() //this is parallel bcz you need components vertically
.addComponent(visualize) //you MUST add components to both horizontal and vertical groups
.addComponent(operations)
.addComponent(sheet)
);
gl.setVerticalGroup(gl.createSequentialGroup() //NOTE that this is sequential
.addComponent(visualize)
.addComponent(operations)
.addGap(50) //you can add gaps if you want
.addComponent(sheet)
);
add(complete);

Because that's how BorderLayout works, take a closer look at How to Use BorderLayout. The CENTRE position will occupy all the remaining space of the frame, where as the NORTH and SOUTH positions will try and honour the preferred sizes of the components.
You could use a GridBagLayout, which will allow you more control over the layout or use a series of compound layouts.
Something like...
setLayout(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
gbc.gridwidth = GridBagConstraints.REMAINDER;
gbc.weightx = 1;
gbc.fill = GridBagConstraints.BOTH;
add(visualize, gbc);
add(operations, gbc);
gbc.gridy = 1;
add(sheet, gbc);
It is generally discouraged to extend from a top level container like JFrame, instead you should use something like JPanel to define your UIs and then add them to the containers you want. This increases there re-usability and makes it easier to use on different containers
You may also like to take a look at How to Use Scroll Panes

SOME of us find GridBagLayout to be a royal pain, and you may not have to use it to do what you want to do.
The idea behind a layout manager is to let the layout manager control the size and position of its components so that you don't have to futz with them. MP is right, GridBag allows you a lot of control, but that also means you have to get a lot of things right to have it do what you want it to do.
So, an alternative: Make a JPanel to hold the visualize and operations panels; give this new panel a BoxLayout with a Y_AXIS orientation, then add them in the order you want them to appear, top-to-bottom.
Then put sheet in the BorderLayout.CENTER of the JFrame. In fact, I think you'll want to take MP's advice and go through a tutorial on JScrollPane; as best I remember, you create the panel, then create the JScrollPane instance with the panel as a construction parameter, then add the scrollpane instance to the JFrame (in the CENTER, in your case).
Being in the center, it will then expand and contract as the user changes window size.
Good luck. Swing takes some getting used to.

Creating a text field that dynamically resizes its width

I'm making what is basically a toolbar that contains a search field and some buttons. I'd like for the search field to grow in size (just the width) when the parent container gets wider, like when the user adjusts the split pane. Currently, the text field and the buttons will remain the same size and whitespace is added on either side as the container is widened. I can achieve this growing effect by using a BorderLayout in the container and putting the buttons on LINE_END and the text field in the CENTER. The problem I have with this is that the text field now becomes taller than a standard text field and it looks ugly. This behavior makes sense as the BorderLayout manager will give all the extra space (this includes vertical and hortizontal space) to the CENTER text field. I've tried to restrict this vertical growth by placing a maximum size on the text field, but BorderLayout will not honor it.
Here's what I've got:
final JTextField searchField = new JTextField("Enter your search terms");
searchField.setMaximumSize(new Dimension(Integer.MAX_VALUE, 25));
final JPanel controls = new JPanel(new BorderLayout());
controls.add(searchField, BorderLayout.CENTER);
controls.add(new JPanel(){{
add(new JButton("Search")); add(new JButton("I'm Feeling Lucky"));
}}, BorderLayout.LINE_END);
It would seem that this behavior is a commonly desired one and it should be easy to implement, but I've had no luck after looking through all the Oracle/Sun tutorials and Google search results.
Anybody have any solutions to this? I need to stick with standard Java Swing components - no third party libraries please.
Thank you!

I would suggest you to use GridBagLayout , it is complicated but it is the most powerful layout.. When you learn it, you would not have any layout issue.
Here is the sample use of gridbaglayout for this question...
import java.awt.BorderLayout;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class GridBagLayoutExample extends JFrame {
GridBagLayoutExample() {
initUI();
}
private void initUI() {
final JTextField searchField = new JTextField("Enter your search terms");
final JPanel controls = new JPanel(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();
c.weightx=1.0;
c.fill=GridBagConstraints.HORIZONTAL;
controls.add(searchField,c);
controls.add(new JPanel(){
{
add(new JButton("Search")); add(new JButton("I'm Feeling Lucky")); }});
setLayout(new BorderLayout());
add(controls, BorderLayout.NORTH);
pack();
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new GridBagLayoutExample().setVisible(true);
}
});
}
}

it's a two part problem:
a) all xxSize (xx = min/max/pref) are mere hints to the LayoutManager. Each and every LayoutManager has its own behaviour if/how/when it respects those hints and if/how/when it violates one or more if the overall space is more or less than would fit the sum of pref for all components in the container. No way but learn which does what (documentation is ... ehem ... suboptimal)
b) JTextField is a bit crazy in allowing its height to grow indefinitely if space allows. Implying that even LayoutManagers which respect max (like f.i. BoxLayout) have no chance to do so, max is Integer.MAX_VALUE (or Short.MAX? forgot). To make it behave, subclass and override maxSize to return the pref height:
#Override
Dimension getMaximumSize() {
Dimension max = super.getMaximumSize();
max.height = getPreferredSize().height;
return max;
}

You should be able to use a horizontal BoxLayout.
searchField.setMaximumSize(new Dimension(Integer.MAX_VALUE, 25));
You should not guess at the height of the text field.
Dimension d = searchField.getPreferredSize();
d.width = Integer.MAX_VALUE;
searchField.setMaximumSize(d);
I know you said you don't want to use 3rd party libraries, but as a side note you might want to look at Text Field Prompt. It allows you to display a message that will disapear when you start typing in the text field.

Using BoxLayout.
JTextField search_field = new JTextField("Enter search term");
JPanel panel = new JPanel();
panel.setLayout(new BoxLayout(panel, BoxLayout.LINE_AXIS));
panel.add(search_field);
This will dynamically change the size of textfield when resizing the frame.