Develop Reference

Add JButton to JScrollPame

I have the following code taken from GeeksforGeeks that displays the contents of a 2-d array in JTable using JScrollPane:
public class JTableExamples {
// frame
JFrame f;
// Table
JTable j;
// Constructor
JTableExamples()
{
// Frame initiallization
f = new JFrame();
// Frame Title
f.setTitle("JTable Example");
// Data to be displayed in the JTable
String[][] data = {
{ "Kundan Kumar Jha", "4031", "CSE" },
{ "Anand Jha", "6014", "IT" }
};
// Column Names
String[] columnNames = { "Name", "Roll Number", "Department" };
// Initializing the JTable
j = new JTable(data, columnNames);
j.setBounds(30, 40, 200, 300);
// adding it to JScrollPane
JScrollPane sp = new JScrollPane(j);
f.add(sp);
// Frame Size
f.setSize(500, 200);
// Frame Visible = true
f.setVisible(true);
}
What I am trying to do is add a simple Component (like JButton) underneath the table but it does not seem to work. I tried modifying the code by adding the JButton to JPanel and adding JPanel to the frame:
JButton button = new JButton("Back");
JPanel panel = new JPanel();
panel.add(button);
f.add(sp);
f.add(panel);
But this simply deletes the entire table and replaces it with a single button. I also tried adding the button to JPanel and adding that JPanel to JScrollPane:
JButton button = new JButton("Back");
JPanel panel = new JPanel();
panel.add(button);
sp.add(panel);
f.add(sp);
But this did not seem to change anything. I also tried to tinker with preferred and maximum size of JScrollPanel to no avail - it always occupies the entire screen and prevents JButton from appearing on the screen.
Not shooting for design here, just functionality: have a JButton appear underneath my JTable. Any suggestions will be greatly appreciated. Thank you in advance!

The default layout manager of a JFrame is the BorderLayout.
f.add(sp);
f.add(panel);
When you don't specify a constraint for the BorderLayout the CENTER is assumed. You can only have a single component added to the CENTER.
Instead your code should be:
f.add(sp, BorderLayout.CENTER);
f.add(panel, BorderLayout.PAGE_END);
Note the default layout manager for a JPanel is the FlowLayout. So the button will be horizontally centered in the panel.
Also, instead of using a JPanel, try adding the button directly to the PAGE_END of the frame to see the difference.
Read the section from the Swing tutorial on Using Layout Manager for more information and examples for using each of the different layout managers to understand the differences of the above suggestions.
Edit:
Is there a way to decrease the height of the table
If you know you have a small table then you can use:
table.setPreferredScrollableViewportSize(table.getPreferredSize());
This will make the scroll pane the size of the table.
Then you use:
//f.setSize(500, 200);
f.pack();
Now all components will be displayed at their preferred size.

I want my JTable at the centre

I want my JTable at the centre of my JFrame and for this purpose i have used setbounds method but it's not doing anything and i don't want to use layout managers.I just want to know that why it's not doing anything?
Here is my code:
tabel=new JTable(data,columnNames);
tabel.setLayout(null);
tabel.setPreferredScrollableViewportSize(new Dimension(500,50));
tabel.setFillsViewportHeight(true);
JScrollPane pane=new JScrollPane(tabel);
pane.setBounds(100,700,200,200);
add(pane);

It's better to use layout managers but if you insist,that you want to move JTable in JFrame by setting layout to null,then you should try the following option:
(1)Make a JPanel in JFrame and add that table to JPanel in this way
JPanel panel=new JPanel();
panel.setBounds(20,300,700,300);
add(panel);
tabel=new JTable(data,columnNames);
tabel.setBounds(100,20,700,400);
tabel.setPreferredScrollableViewportSize(new Dimension(500,50));
tabel.setFillsViewportHeight(true);
JScrollPane pane=new JScrollPane(tabel);
panel.add(pane);

You should add everything to a JPanel, and then set the layout of the JPanel to a border layout. Add the table to the JPanel and then position it at the center. This is the easiest way to do it. Layouts may seem complicated and inconvenient at first but once you learn them, you quickly realise they are a million times easier that setting bounds and null layouts. Here is a link to learn about border layout: https://docs.oracle.com/javase/tutorial/uiswing/layout/border.html

You are adding JTable to a JFrame(Top level component).This may get you going
JPanel tablePanel = new JPanel(new GridBagLayout());
GridBagConstraints layout= new GridBagConstraints();
JTable jtable = new JTable();
jtable.setPreferredScrollableViewportSize(new Dimension(500,50));
jtable.setFillsViewportHeight(true);
layout.fill = GridBagConstraints.BOTH;
layout.weightx = 1;
layout.weighty = 1;
layout.gridx = 0;
layout.insets = new Insets(10,10,10,10);
tablePanel.add(new JScrollPane(jtable), layout)
You may want to set layout dimensions and insets according to your jtable.

how to add scrollbar to textarea in java

the jscrollpane that I am adding doesnt appearin my textarea
textArea = new JTextArea();
scroll = new JScrollPane(textArea);
scroll.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
this.add(textArea);
this.add(scroll);
this.setSize(1000, 600);
this.setLayout(new BorderLayout());
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLocationRelativeTo(null);

textArea = new JTextArea();
scroll = new JScrollPane(textArea);
//this.add(textArea); // get rid of this
this.add(scroll);
You create the scrollpane with the text area, but then the next statement removes the text area from the scrollpane because a component can only have a single parent.
Get rid of that statement and just add the scrollpane to the frame.
Then scrollbars will appear automatically as you add data to the text area.
Also you should create the text area using something like:
textArea = new JTextArea(5, 20);
to give a suggestion on how big to make the text area.
I did what you said but still nothing happens
Another problem is that you need to set the layout manager BEFORE you start adding components to the frame (or panel).

Remove this.add(textArea); and add scroll.setSize( 100, 100 ); will also work for you.

JTextArea that needs to grow with parent panel

I want to make my JTextArea field as big as it can be in current JPanel. How to do that?
Now it is like this:
JPanel statusBar = new StatusBar(project);
JTextArea outputBox = new JTextArea(1, 50);
outputBox.setEditable(true);
statusBar.add(outputBox);

The default layout manager of JPanel is FlowLayout, which wouldn't let the text area fill the entire available space in the panel.
Using BorderLayout should work well:
statusBar.setLayout( new BorderLayout() );
JTextArea outputBox = new JTextArea(1, 50);
outputBox.setEditable(true);
statusBar.add(outputBox, BorderLayout.CENTER);

You need a layout manager on the JPanel. If its just the JTextArea contained within it and you need to maximise it you can use a simple GridLayout:
statusBar.setLayout(new GridLayout(1,1));

How do i get vertical scrolling to JPanel?

I have written a code in java using swing, so that I will have a JscrollPane added to JPanel and then I will add buttons of fixed size to JPanel in vertical fashion
JPanel panel=new JPanel();
panel.setBackground(Color.WHITE);
int v=ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS;
int h=ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS;
JScrollPane jsp=new JScrollPane(panel,v,h);
jsp.setPreferredSize(new Dimension(600,600));
jsp.setBounds(150,670,850,200);
frame.add(jsp);
then I am adding buttons to it at run time.
for(i=0;i<n;i++)
{
button[i]=new JButton();
button[i].setBounds(20,y,120,120);
button[i].setSize(120,120);
button[i].setToolTipText(file[i].toString());
button[i].setIcon(Icon);
panel.add(button[i]);
y=y+140;
}
I want to add a buttons one below the other...(i.e I want a vertical scrollbar)
i.e. button1
button2
'
'
but above code is giving me buttons in a line (i.e. I am getting horizontal scrollbar)
i.e. button1 button2...
another problem is the size of the buttons. Using btn.setSize() is not affecting size at all...
can anybody help me?

You must use an appropriate Layoutmanager like GridLayout, Boxlayout or GridBagLayout for the panel.
It depends what else you want to put into the panel.
GridLayout is easier to use IMO:
JPanel panel = new JPanel();
panel.setLayout(new GridLayout(0, 1)); // any number of rows, 1 column
...
panel.add(button[i]);
BoxLayout is almost as easy:
JPanel panel = new JPanel();
panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
...
panel.add(button[i]);
GridBagLayout is more powerful, allowing more than one column, components spanning more than one cell, ... needs a GridBagConstraints to add the elements:
JPanel panel = new JPanel();
panel.setLayout(new GridBagLayout());
GridBagConstraints constraints = new GridBagConstraints(
0, RELATIVE, // x = 0, y = below previous element
1, 1, // cell width = 1, cell height = 1
0.0, 0.0 // how to distribute space: weightx = 0.0, weighty = 0,0
GridBagConstraints.CENTER, // anchor
GridBagConstraints.BOTH, // fill
new Insets(0, 0, 0, 0), // cell insets
0, 0); // internal padding
...
panel.add(button[i], constraints);
Have a look at this tutorial: Laying Out Components Within a Container (The visual guide is a good start point)
EDIT:
you can also lay out the components by hand, that is, specify the location and size of each component in the container. For this you must set the LayoutManager to null so the default manager gets removed.
JPanel panel = new JPanel();
panel.setLayout(null);
...
button[i].setLocation(x, y);
button[i].setSize(width, heigth);
// OR button[i].setBounds(x, y, width, height);
panel.add(button[i]);

You need to define an appropriate LayoutManager for your JPanel, which is responsible for how the Components added to it are positioned. The default LayoutManager is FlowLayout, which lays out Components left-to-right. For laying out Components vertically you should consider using BoxLayout or GridBagLayout.

You have to set LayoutManager for JPanel or use Box(BoxLayout.Y_AXIS) instead.

For the size of buttons use preferredSize
For your layout problem you need to change the layout manager to one that does a vertical layout. For playing around purposes you can use BoxLayout like this:
panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));

This is much easier if you let the layout manager do its work.
In Swing, the way the components are layout over other component ( a panel for instance ) is using a layout manager.
It is used to avoid having to compute the coordinates of all the components against each other each time the container component resizes, or a new component is added.
There are different layout mangers, the one that you need here is BoxLayout.
By using this layout you don't need to specify the button position, nor its size. The layout manager query each component and use that information to place them in the correct position and size.
For instance the following frame
Was created this ( modified version of your ) code:
import javax.swing.*;
import java.awt.*;
public class ScrollTest {
private JPanel panel;
private Icon[] icons = new Icon[3];
public void main() {
panel =new JPanel();
// Use top to bottom layout in a column
panel.setLayout( new BoxLayout( panel, BoxLayout.Y_AXIS ));
panel.setBackground(Color.WHITE);
int v=ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS;
int h=ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS;
JScrollPane jsp=new JScrollPane(panel,v,h);
jsp.setPreferredSize(new Dimension(600,600));
jsp.setBounds(150,670,850,200);
JFrame frame = new JFrame();
frame.add(jsp);
// my addition to load sample icons
loadImages();
// simulate dynamic buttons
addButtons();
frame.pack();
frame.setVisible( true );
}
void loadImages() {
icons[0] = new ImageIcon( "a.png" );
icons[1] = new ImageIcon( "b.png" );
icons[2] = new ImageIcon( "c.png" );
}
void addButtons() {
for( int i = 0 ; i < icons.length ; i++ ) {
JButton button = new JButton();
Icon icon = icons[i];
button.setIcon( icon );
// Set the button size to be the same as the icon size
// The preferred size is used by the layout manager
// to know what the component "better" size is.
button.setPreferredSize( new Dimension( icon.getIconWidth(),
icon.getIconHeight() ) );
// This is IMPORTANT. The maximum size is used bythe layout manager
// to know "how big" could this component be.
button.setMaximumSize( button.getPreferredSize() );
panel.add( button );
}
}
public static void main( String ... args ) {
new ScrollTest().main();
}
}
I hope this helps.

One can also get a vertical scrolling for JPanel with SpringLayout. It's possible if panel's vertical size will be defined by setting a constraint SpringLayout.SOUTH. This can be done like this:
JPanel panel = new JPanel();
SpringLayout panelLayout = new SpringLayout();
panel.setLayout(panelLayout);
// Adding components to the panel here
// .....
// That's what defines panel's exact size and makes its scrolling possible
panelLayout.putConstraint(SpringLayout.SOUTH, panel, 0,
SpringLayout.SOUTH, lastComponentOfThePanel);
JScrollPane panelScrollPane = new JScrollPane(panel);
where lastComponentOfThePanel is a component at the bottom of a panel.
Hope this will help somebody. In my opinion, SpringLayout is very powerful layout manager, and sometimes it's very difficult or almost impossible to replace this one with GridBagLayout.

What about?
JScrollPane scrollPane = new JScrollPane(yourpanel);
container.add(scrollPane);