1.頂層元件JFrame或者對話方塊JDialog居中

Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
Dimension frameSize = frame.getSize();
if (frameSize.height > screenSize.height)
    frameSize.height = screenSize.height;       
if (frameSize.width > screenSize.width)
    frameSize.width = screenSize.width;       
frame.setLocation((screenSize.width-frameSize.width)/2,screenSize.height-frameSize.height) / 2);
 

Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
screenSize = Toolkit.getDefaultToolkit().getScreenSize();
frame.setPreferredSize(new Dimension(512,450));           
int frameWidth = this.getPreferredSize().width;
int frameHeight = this.getPreferredSize().height;
frame.setSize(frameWidth, frameHeight);
frame.setLocation((screenSize.width - frameWidth) / 2,(screenSize.height - frameHeight) / 2);
 

Font vFont = new Font("Dialog", Font.PLAIN, 13);
UIManager.put("ToolTip.font", vFont);
UIManager.put("Table.font", vFont);
UIManager.put("TableHeader.font", vFont);
UIManager.put("TextField.font", vFont);
UIManager.put("ComboBox.font", vFont);
UIManager.put("TextField.font", vFont);
UIManager.put("PasswordField.font", vFont);
UIManager.put("TextArea.font", vFont);