为什么JOptionPane.showmessagedialog会弹出两次一样的对话框来？

public void setVisible(boolean b) {
super.setVisible(b);
if (b)
JOptionPane
.showMessageDialog(
null,
"this software will be working now, Please press the button ENTER ",
"Notes", JOptionPane.WARNING_MESSAGE);
}
为什么JOptionPane.showmessagedialog会弹出两次一样的对话框来？