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Verifying JTextFields that may not get focus

I've been looking at the java trail on input verification and I was hoping someone could just confirm that the InputVerifier class is the best way to approach my problem.
I've a number of JTextFields in a JPanel, with a submit button. Each Field is initially blank. The problem is that the Verifier class works on condition of losing focus, but with multiple fields nothing ensures that each gets focus in the first place. For example you could enter a valid entry into the first field, and click submit, despite verification being needed on the following fields.
I'm sure I could rig something together, whereby when the submit button is pressed it checks the relevant JTextAreas for any input at all and assigns focus to the first one that still requires data, but I was hoping that there was a more elegant way to check input? Especially as the InputVerifier can be set for components rather than just textfields. Tracking or customising focus doesn't really help either as several of the fields are optional but still in a logical order (so I wouldn't want to force focus in an unnatural order just to ensure data entry)
I thought about adding the InputVerifier to a containing component, or the submit button, but again, I can't get around the problem of focus.

The problem is that the Verifier class works on condition of losing focus, but with multiple fields nothing ensures that each gets focus in the first place. For example you could enter a valid entry into the first field, and click submit, despite verification being needed on the following fields.
That is correct. The InputVerifier only works when the component loses focus.
Typically, there are two types of editing done on a forum:
field level edits. These are edits to make sure a component contains valid data. That is numbers are number, postal codes are validated for proper format etc. These type of edits can by done using the InputVerifier
form level edits. These ensure that all mandatory fields for the form are entered. This is done when you click the "Submit" button.
If all the fields are mandatory you could try disabling the "Submit" button until data has been entered in all text fields by using logic something like:
import java.awt.*;
import java.awt.event.*;
import java.util.List;
import java.util.ArrayList;
import javax.swing.*;
import javax.swing.event.*;
public class DataEntered implements DocumentListener
{
private JButton button;
private List<JTextField> textFields = new ArrayList<JTextField>();
public DataEntered(JButton button)
{
this.button = button;
}
public void addTextField(JTextField textField)
{
textFields.add( textField );
textField.getDocument().addDocumentListener( this );
}
public boolean isDataEntered()
{
for (JTextField textField : textFields)
{
if (textField.getText().trim().length() == 0)
return false;
}
return true;
}
#Override
public void insertUpdate(DocumentEvent e)
{
checkData();
}
#Override
public void removeUpdate(DocumentEvent e)
{
checkData();
}
#Override
public void changedUpdate(DocumentEvent e) {}
private void checkData()
{
button.setEnabled( isDataEntered() );
}
private static void createAndShowUI()
{
JButton submit = new JButton( "Submit" );
submit.setEnabled( false );
JTextField textField1 = new JTextField(10);
JTextField textField2 = new JTextField(10);
DataEntered de = new DataEntered( submit );
de.addTextField( textField1 );
de.addTextField( textField2 );
JFrame frame = new JFrame("SSCCE");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(textField1, BorderLayout.WEST);
frame.add(textField2, BorderLayout.EAST);
frame.add(submit, BorderLayout.SOUTH);
frame.pack();
frame.setLocationByPlatform( true );
frame.setVisible( true );
}
public static void main(String[] args)
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
createAndShowUI();
}
});
}
}
Just remember using these approach you don't get any message if data is missing.
I'm sure I could rig something together, whereby when the submit button is pressed it checks the relevant JTextAreas for any input at all and assigns focus to the first one that still requires data, but I was hoping that there was a more elegant way to check input?
This is a perfectly reasonable approach as it give the user visual feedback where the problem is.

How to edit a JComboBox with text selected in JEditorPane

I have a UI with two components - a JEditorPane and a JComboBox. My goal is to be able to type something into the JEditorPane, select a portion of the text, and while it is still selected type and/or select a value in an editable JComboBox.
This is for a text editor type of program where I want to change the font size of just the selected text in the editor pane. Where the font size is coming from the editable combo box. To clarify, I'm not asking how to apply styles to the text, I'm asking how to select a value in the combo box without losing the focus/selection in the JEditorPane.
Here's the code for the UI, but I wasn't sure where to begin doing anything with the focus...
public static void main(String [] args)
{
JFrame frame = new JFrame();
JPanel contentPane = new JPanel();
JComboBox<String> combo = new JComboBox(new String [] {"Hello", "World"});
contentPane.add(combo);
JEditorPane editor = new JEditorPane();
contentPane.add(editor);
frame.setContentPane(contentPane);
frame.pack();
frame.setVisible(true);
}

I'm asking how to select a value in the combo box without losing the focus/selection in the JEditorPane.
You don't lose the selection of the text in the editor pane when you select an item from the combo box. The selection remains, but it is just not painted until the editor pane regains focus.
So the easiest way to do this is to use a JMenuItem. Read the section from the Swing tutorial on Text Component Features for an example that does this.
If you still want to use the combo box then you can add Integer values to the combo box then the code in your ActionListener for the combo box would look something like:
#Override
public void actionPerformed(ActionEvent e)
{
Integer value = (Integer)comboBox.getSelectedItem();
Action action = new StyledEditorKit.FontSizeAction("Font size", value);
action.actionPerformed(null);
}
The StyledEditorKit actions extend from TextAction. The TextAction knows the last text component that had focus and therefore the font change is applied to that text component.
If you really want the text field to show the selection then you need to create a custom Caret and override the focusLost method to NOT invoke setSelectionVisible(false) (which is the default behaviour.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;
public class DefaultCaretTest extends JFrame
{
public DefaultCaretTest()
{
JTextField textField1 = new JTextField("Text Field1 ");
JTextField textField2 = new JTextField("Text Field2 ");
textField1.setCaret(new SelectionCaret());
textField2.setCaret(new SelectionCaret());
textField1.select(5, 11);
textField2.select(5, 11);
((DefaultCaret)textField2.getCaret()).setSelectionVisible(true);
add(textField1, BorderLayout.WEST);
add(textField2, BorderLayout.EAST);
}
static class SelectionCaret extends DefaultCaret
{
public SelectionCaret()
{
setBlinkRate( UIManager.getInt("TextField.caretBlinkRate") );
}
public void focusGained(FocusEvent e)
{
setVisible(true);
setSelectionVisible(true);
}
public void focusLost(FocusEvent e)
{
setVisible(false);
}
}
public static void main(String[] args)
{
DefaultCaretTest frame = new DefaultCaretTest();
frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
frame.pack();
frame.setLocationRelativeTo( null );
frame.setVisible(true);
}
}
Of course the selection will remain when focus is on any other component, not just the combo box.
You can also use:
comboBox.setFocusable(false);
Since the combo box can't gain focus the focus will remain on the text component, but the problem with this is that the user won't be able to use the keyboard to select a font size from the combo box. A proper GUI design always allows the user to use either the keyboard or the mouse to perform an action.

How to construct a JTextfield, and how to use the method selectAll()

I want to construct a Swing component JTextField, here is my Code
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class JTextFieldGui{
JTextField textField;
JLabel labelInput;
JLabel labelOutput;
public static void main(String[] args) {
JTextFieldGui gui = new JTextFieldGui();
gui.go();
}
public void go(){
JFrame frame = new JFrame();
JPanel panelInput = new JPanel();
JPanel panelOutput = new JPanel();
labelInput = new JLabel("Your first name: ");
labelOutput = new JLabel("Enter your name, and you will see it here.");
textField = new JTextField(20);
JButton enter = new JButton("Enter");
JButton selectAll = new JButton("Select all text");
frame.setSize(300,200);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
panelInput.setLayout(new BoxLayout(panelInput, BoxLayout.X_AXIS));
textField.addActionListener(new LabelActionListener());
enter.addActionListener(new LabelActionListener());
selectAll.addActionListener(new TextFieldActionlistener());
frame.getContentPane().add(BorderLayout.NORTH, panelInput);
panelInput.add(labelInput);
panelInput.add(textField);
panelInput.add(enter);
panelInput.add(selectAll);
frame.getContentPane().add(BorderLayout.CENTER, panelOutput);
panelOutput.add(labelOutput);
}
class LabelActionListener implements ActionListener{
public void actionPerformed(ActionEvent event){
labelOutput.setText(textField.getText());
}
}
class TextFieldActionlistener implements ActionListener{
public void actionPerformed(ActionEvent event){
textField.selectAll();
}
}
}
Question1: I define the width of the text field in 20 columns, but it always take up a row, like image:
Question2: how to use the selectAll() method, I use it in a listener of the button selectAll, but when I click the button, nothing happens, why

I define the width of the text field in 20 columns, but it always take up a row,
This is the rule of a BoxLayout. A component is resized to fill the space available. A JTextField doesn't have a maximum size so it grows. The buttons and label do have a maximum size so they don't grow.
Don't use a BoxLayout, just use a FlowLayout. It will automatically leave space between each component which is a better layout.
I use it in a listener of the button selectAll, but when I click the button, nothing happens, why
Focus is still on the button. The selected text only displays when the text field has focus.
So in he listener code you need to add:
textField.requestFocusInWindow();
The following code is old:
frame.getContentPane().add(BorderLayout.NORTH, panelInput);
you don't need to get the content pane. You can just add the component to the frame.
the constraint should be the second parameter
there are new constraints to make the names more meaningful
So the code should be:
frame.add(panelInput, BorderLayout.PAGE_START, panelInput);
See the section from the Swing tutorial on How to Use BorderLayout for more information.

What text input component last had the focus?

Suppose I have a Java application that has more than one component in which you can enter text. Now suppose this application also has a dialog that lets you insert a single character (like the dialog in Word that comes up when you select Insert from the Edit menu) into those components. You want it to insert the character into whichever text component last had the focus.
But how do you know which text component last had the focus?
I could keep track of this manually, by having each text component report to the application whenever it gets the focus and then have the application insert the new character into whichever component that last had the focus.
But this must be a common problem (consider Paste buttons in tool bars---how does it know where to paste it into?). Is there something already built in to Swing that lets you get a handle to the last text component that had the focus? Or do I need to write this myself?

Is there something already built in to Swing that lets you get a handle to the last text component that had the focus?
You create an Action that extends TextAction. The TextAction class has a method that allows you to obtain the last text component that had focus.
Edit:
You can create your own Action and do whatever you want. The Action can then be added to any JMenuItem or JButton. For example:
class SelectAll extends TextAction
{
public SelectAll()
{
super("Select All");
}
public void actionPerformed(ActionEvent e)
{
JTextComponent component = getFocusedComponent();
component.selectAll();
}
}
If you just want to insert a character at the caret position of the text field then you can probably just do
component.replaceSelection(...);
Edit 2:
I don't understand what the confusion is with this answer. Here is a simple example:
select some text
use the mouse to click on the check box
tab or use the mouse to click on the "Cut" button
It doesn't matter that the text field doesn't currently have focus when the Action is invoked. The TextAction tracks the last text component that had focus.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;
public class TextActionTest extends JFrame
{
JTextField textField = new JTextField("Select Me");
JTabbedPane tabbedPane;
public TextActionTest()
{
add(textField, BorderLayout.NORTH);
add(new JCheckBox("Click Me!"));
add(new JButton(new CutAction()), BorderLayout.SOUTH);
}
public static void main(String[] args)
{
TextActionTest frame = new TextActionTest();
frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
frame.pack();
frame.setLocationRelativeTo( null );
frame.setVisible(true);
}
class CutAction extends TextAction
{
public CutAction()
{
super("Click to Cut Text");
}
public void actionPerformed(ActionEvent e)
{
JTextComponent component = getFocusedComponent();
// JTextComponent component = getTextComponent(e);
component.cut();
}
}
}

Just like suggested by #lesmana (+1 for that).
Here you have an example that shows that on focusLost the focus listener returns the previously focused component.
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
public class Focusing
{
public static void main(String[] args)
{
JPanel p = new JPanel();
JTextField tf1 = new JTextField(6);
tf1.setName("tf1");
p.add(tf1);
JTextField tf2 = new JTextField(6);
tf2.setName("tf2");
p.add(tf2);
FocusListener fl = new FocusListener()
{
#Override
public void focusGained(FocusEvent e)
{
System.out.println("focusGained e.getSource().c=" + ((JComponent) e.getSource()).getName());
}
#Override
public void focusLost(FocusEvent e)
{
System.out.println("focusLost e.getSource().c=" + ((JComponent) e.getSource()).getName());
}
};
tf1.addFocusListener(fl);
tf2.addFocusListener(fl);
JPanel contentPane = new JPanel();
contentPane.add(p);
JFrame f = new JFrame();
f.setContentPane(contentPane);
f.setSize(800, 600);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setVisible(true);
}
}
All the best, Boro.

I've never done this directly, but you could look into the FocusEvents and the Focus Subsystem.
Hopefully there is something in the Focus Subsystem that would fire events that you could listen for.

You can register a FocusListener to every text component. The FocusEvent object has a reference to the last component which had focus.

How can I display red text in a JTextArea?

I want to show error(text) in result in red color after compiling exec file
and display it in textarea of gui using swing in java.

A normal JTextArea doesn't support fancy things like different colors of text. However, there are similar components that do. See http://java.sun.com/docs/books/tutorial/uiswing/components/text.html

JEditorPane can get content formatted in HTML. The official Sun tutorial also gives some insight:
The JTextArea class provides a component that displays multiple lines of text and optionally allows the user to edit the text. If you need to obtain only one line of input from the user, you should use a text field. If you want the text area to display its text using multiple fonts or other styles, you should use an editor pane or text pane. If the displayed text has a limited length and is never edited by the user, use a label.

Here's a quick example of adding text to a JEditorPane using AttributeSet and StyleConstants.
This brings up a little frame with a JEditorPane and you can use it to add text of lots of colors without using HTML.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.text.*;
import javax.swing.border.*;
public class TextColor extends JFrame implements ActionListener {
JTextPane myTextPane;
JTextArea inputTextArea;
public TextColor() {
super();
JPanel temp = new JPanel(new BorderLayout());
inputTextArea = new JTextArea();
JButton btn = new JButton("Add");
btn.addActionListener(this);
temp.add(btn, BorderLayout.SOUTH);
temp.add(inputTextArea, BorderLayout.NORTH);
this.getContentPane().add(temp, BorderLayout.SOUTH);
myTextPane = new JTextPane();
myTextPane.setBorder(new EtchedBorder());
this.getContentPane().add(myTextPane, BorderLayout.CENTER);
this.setSize(600, 600);
this.setVisible(true);
}
public void actionPerformed(ActionEvent ae) {
Color newTextColor = JColorChooser.showDialog(this, "Choose a Color", Color.black);
//here is where we change the colors
SimpleAttributeSet sas = new SimpleAttributeSet(myTextPane.getCharacterAttributes());
StyleConstants.setForeground(sas, newTextColor);
try {
myTextPane.getDocument().insertString(myTextPane.getDocument().getLength(),
inputTextArea.getText(), sas);
} catch (BadLocationException ble) {
ble.printStackTrace();
}
}
public static void main(String args[]) {
new TextColor();
}
}

Smita,
take care to paste snippet of your code so that one can understand where exactly problem is or help is required.
Coming to your problem,
To the best of my knowledge, there is no way to set different colors for different text elements in textArea in java. You can set only one color for all.
Alternative is to use JTextPane.
See if following code helps your cause.
String text = "Some Text..."; //This can be any piece of string in your code like
output of your program...
JTextPane myTextPane = new JTextPane();
SimpleAttributeSet sas = new SimpleAttributeSet(myTextPane.getCharacterAttributes());
// As what error you were referring was not clear, I assume there is some code in your
program which pops out some error statement. For convenience I use Exception here..
if( text.contains("Exception") ) //Checking if your output contains Exception...
{
StyleConstants.setForeground(sas, Color.red); //Changing the color of
StyleConstants.setItalic(sas, true);
try
{
myTextPane.getDocument().insertString
(
myTextPane.getDocument().getLength(),
text + "\n",
sas
);
}
catch( BadLocationException ble )
{
text.append(ble.getMessage());
}
}
else
{
StyleConstants.setForeground(sas, Color.GREEN);
try
{
myTextPane.getDocument().insertString
(
myTextPane.getDocument().getLength(),
text + "\n",
sas
);
}
catch(BadLocationException ble)
{
text.append(ble.getMessage());
}
}
I guess this will solve your problem with few modifications.
Thanks.
Sushil