Question

JList 中的内容怎么让它居中

Jlist中添加的内容都是默认靠左的，如何让他居中呢？

Answer 1

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;

/* ListDemo.java requires no other files. */
public class ListDemo extends JPanel
implements ListSelectionListener {
private JList list;
private DefaultListModel listModel;

private static final String hireString = "Hire";
private static final String fireString = "Fire";
private JButton fireButton;
private JTextField employeeName;

public ListDemo() {
super(new BorderLayout());

listModel = new DefaultListModel();
listModel.addElement("Debbie Scott");
listModel.addElement("Scott Hommel");
listModel.addElement("Sharon Zakhour");

//Create the list and put it in a scroll pane.
list = new JList(listModel);
list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
list.setSelectedIndex(0);
list.addListSelectionListener(this);
list.setVisibleRowCount(5);
list.setCellRenderer(new MyCellRenderer()); ///////////////////////<---------------
JScrollPane listScrollPane = new JScrollPane(list);

JButton hireButton = new JButton(hireString);
HireListener hireListener = new HireListener(hireButton);
hireButton.setActionCommand(hireString);
hireButton.addActionListener(hireListener);
hireButton.setEnabled(false);

fireButton = new JButton(fireString);
fireButton.setActionCommand(fireString);
fireButton.addActionListener(new FireListener());

employeeName = new JTextField(10);
employeeName.addActionListener(hireListener);
employeeName.getDocument().addDocumentListener(hireListener);
String name = listModel.getElementAt(
list.getSelectedIndex()).toString();

//Create a panel that uses BoxLayout.
JPanel buttonPane = new JPanel();
buttonPane.setLayout(new BoxLayout(buttonPane,
BoxLayout.LINE_AXIS));
buttonPane.add(fireButton);
buttonPane.add(Box.createHorizontalStrut(5));
buttonPane.add(new JSeparator(SwingConstants.VERTICAL));
buttonPane.add(Box.createHorizontalStrut(5));
buttonPane.add(employeeName);
buttonPane.add(hireButton);
buttonPane.setBorder(BorderFactory.createEmptyBorder(5,5,5,5));

add(listScrollPane, BorderLayout.CENTER);
add(buttonPane, BorderLayout.PAGE_END);
}

class FireListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
//This method can be called only if
//there's a valid selection
//so go ahead and remove whatever's selected.
int index = list.getSelectedIndex();
listModel.remove(index);

int size = listModel.getSize();

if (size == 0) { //Nobody's left, disable firing.
fireButton.setEnabled(false);

} else { //Select an index.
if (index == listModel.getSize()) {
//removed item in last position
index--;
}

list.setSelectedIndex(index);
list.ensureIndexIsVisible(index);
}
}
}

//This listener is shared by the text field and the hire button.
class HireListener implements ActionListener, DocumentListener {
private boolean alreadyEnabled = false;
private JButton button;

public HireListener(JButton button) {
this.button = button;
}

//Required by ActionListener.
public void actionPerformed(ActionEvent e) {
String name = employeeName.getText();

//User didn't type in a unique name...
if (name.equals("") || alreadyInList(name)) {
Toolkit.getDefaultToolkit().beep();
employeeName.requestFocusInWindow();
employeeName.selectAll();
return;
}

int index = list.getSelectedIndex(); //get selected index
if (index == -1) { //no selection, so insert at beginning
index = 0;
} else { //add after the selected item
index++;
}

listModel.insertElementAt(employeeName.getText(), index);
//If we just wanted to add to the end, we'd do this:
//listModel.addElement(employeeName.getText());

//Reset the text field.
employeeName.requestFocusInWindow();
employeeName.setText("");

//Select the new item and make it visible.
list.setSelectedIndex(index);
list.ensureIndexIsVisible(index);
}

//This method tests for string equality. You could certainly
//get more sophisticated about the algorithm. For example,
//you might want to ignore white space and capitalization.
protected boolean alreadyInList(String name) {
return listModel.contains(name);
}

//Required by DocumentListener.
public void insertUpdate(DocumentEvent e) {
enableButton();
}

//Required by DocumentListener.
public void removeUpdate(DocumentEvent e) {
handleEmptyTextField(e);
}

//Required by DocumentListener.
public void changedUpdate(DocumentEvent e) {
if (!handleEmptyTextField(e)) {
enableButton();
}
}

private void enableButton() {
if (!alreadyEnabled) {
button.setEnabled(true);
}
}

private boolean handleEmptyTextField(DocumentEvent e) {
if (e.getDocument().getLength() <= 0) {
button.setEnabled(false);
alreadyEnabled = false;
return true;
}
return false;
}
}

//This method is required by ListSelectionListener.
public void valueChanged(ListSelectionEvent e) {
if (e.getValueIsAdjusting() == false) {

if (list.getSelectedIndex() == -1) {
//No selection, disable fire button.
fireButton.setEnabled(false);

} else {
//Selection, enable the fire button.
fireButton.setEnabled(true);
}
}
}

/**
* Create the GUI and show it. For thread safety,
* this method should be invoked from the
* event-dispatching thread.
*/
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("ListDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

//Create and set up the content pane.
JComponent newContentPane = new ListDemo();
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();
}
});
}

///////////////////////////////
class MyCellRenderer extends JLabel implements ListCellRenderer {
public MyCellRenderer() {
setOpaque(true);
}
public Component getListCellRendererComponent(
JList list,
Object value,
int index,
boolean isSelected,
boolean cellHasFocus)
{

setText(value.toString());
setHorizontalAlignment(JLabel.CENTER); ///////// <------------
setBackground(isSelected ? Color.red : Color.white);
setForeground(isSelected ? Color.white : Color.black);
return this;
}
/////////////////////////////////
}

}