1.QCoreApplication
描述：The QCoreApplication class provides an event loop for console Qt applications.
2.QApplication
描述：The QApplication class manages the GUI application's control flow and main settings.
3.QWidget
描述：The QWidget class is the base class of all user interface objects.
方法：
void setWindowTitle(const QString &)
设置窗口标题
void QWidget::setLayout(QLayout * layout)
Sets the layout manager for this widget to layout.
void QWidget::show() [slot]
Shows the widget and its child widgets.
4.QHBoxLayout
描述：The QHBoxLayout class lines up widgets horizontally.
方法：
void QBoxLayout::addWidget(QWidget * widget, int stretch = 0, Qt::Alignment alignment = 0)
Adds widget to the end of this box layout, with a stretch factor of stretch and alignment alignment.
Inherited from QBoxLayout