D-Bus adaptor example does not actually build

http://doc.qt.io/qt-5/qdbusadaptorexample.html

src/dbus/doc/snippets/code/doc_src_qdbusadaptors.cpp

This example code does not actually build.

This embarrasses beginners.

After adding

#include <QApplication>
#include <QDBusAbstractAdaptor>
#include <QDBusConnection>

Following error shown:

g++ -c -pipe -O2 -Wall -W -D_REENTRANT -fPIC -DQT_NO_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_DBUS_LIB -DQT_CORE_LIB -I. -isystem /usr/include/qt5 -isystem /usr/include/qt5/QtWidgets -isystem /usr/include/qt5/QtGui -isystem /usr/include/qt5/QtDBus -isystem /usr/include/qt5/QtCore -I. -isystem /usr/include/libdrm -I/usr/lib64/qt5/mkspecs/linux-g++ -o dbusadaptor.o dbusadaptor.cpp
dbusadaptor.cpp: In member function 'QString MainApplicationAdaptor::caption()':
dbusadaptor.cpp:77:18: error: 'class QApplication' has no member named 'hasMainWindow'; did you mean 'activeWindow'?
         if (app->hasMainWindow())
                  ^~~~~~~~~~~~~
                  activeWindow
dbusadaptor.cpp:78:25: error: 'class QApplication' has no member named 'mainWindow'; did you mean 'allWindows'?
             return app->mainWindow()->caption();
                         ^~~~~~~~~~
                         allWindows
dbusadaptor.cpp: In member function 'void MainApplicationAdaptor::setCaption(const QString&)':
dbusadaptor.cpp:84:18: error: 'class QApplication' has no member named 'hasMainWindow'; did you mean 'activeWindow'?
         if (app->hasMainWindow())
                  ^~~~~~~~~~~~~
                  activeWindow
dbusadaptor.cpp:85:18: error: 'class QApplication' has no member named 'mainWindow'; did you mean 'allWindows'?
             app->mainWindow()->setCaption(newCaption);
                  ^~~~~~~~~~
                  allWindows
dbusadaptor.cpp: In member function 'void MainApplicationAdaptor::reparseConfiguration()':
dbusadaptor.cpp:103:12: error: 'class QApplication' has no member named 'reparseConfiguration'
     { app->reparseConfiguration(); }
            ^~~~~~~~~~~~~~~~~~~~
dbusadaptor.cpp: In member function 'QString MainApplicationAdaptor::mainWindowObject()':
dbusadaptor.cpp:107:18: error: 'class QApplication' has no member named 'hasMainWindow'; did you mean 'activeWindow'?
         if (app->hasMainWindow())
                  ^~~~~~~~~~~~~
                  activeWindow
dbusadaptor.cpp: In member function 'void MainApplicationAdaptor::setSessionManagement(bool)':
dbusadaptor.cpp:115:17: error: 'class QApplication' has no member named 'enableSessionManagement'
            app->enableSessionManagement();
                 ^~~~~~~~~~~~~~~~~~~~~~~
dbusadaptor.cpp:117:17: error: 'class QApplication' has no member named 'disableSessionManagement'
            app->disableSessionManagement();
                 ^~~~~~~~~~~~~~~~~~~~~~~~
dbusadaptor.cpp: In member function 'void MainApplicationAdaptor::focusChangedSlot(QWidget*, QWidget*)':
dbusadaptor.cpp:123:25: error: 'class QApplication' has no member named 'mainWindow'; did you mean 'allWindows'?
         if (now == app->mainWindow())
                         ^~~~~~~~~~
                         allWindows
dbusadaptor.cpp: At global scope:
dbusadaptor.cpp:135:1: error: 'interface' does not name a type
 interface org.kde.DBus.MainApplication
 ^~~~~~~~~
dbusadaptor.cpp: In function 'int main(int, char**)':
dbusadaptor.cpp:159:35: error: no matching function for call to 'MainApplicationAdaptor::MainApplicationAdaptor(QApplication&)'
     new MainApplicationAdaptor(app);
                                   ^
dbusadaptor.cpp:67:5: note: candidate: 'MainApplicationAdaptor::MainApplicationAdaptor(QApplication*)'
     MainApplicationAdaptor(QApplication *application)
     ^~~~~~~~~~~~~~~~~~~~~~
dbusadaptor.cpp:67:5: note:   no known conversion for argument 1 from 'QApplication' to 'QApplication*'
dbusadaptor.cpp:165:6: error: expected identifier before '...' token
     [...]
      ^~~
dbusadaptor.cpp: In lambda function:
dbusadaptor.cpp:167:5: error: expected '{' before 'app'
     app.exec();
     ^~~
dbusadaptor.cpp: In function 'int main(int, char**)':
dbusadaptor.cpp:165:10: error: expected ';' before 'app'
     [...]
          ^
          ;
dbusadaptor.cpp:167:5:
     app.exec();
     ~~~
dbusadaptor.cpp: At global scope:
dbusadaptor.cpp:173:7: error: redefinition of 'class MainApplicationAdaptor'
 class MainApplicationAdaptor: public QDBusAbstractAdaptor
       ^~~~~~~~~~~~~~~~~~~~~~
dbusadaptor.cpp:55:7: note: previous definition of 'class MainApplicationAdaptor'
 class MainApplicationAdaptor: public QDBusAbstractAdaptor
       ^~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/qt5/QtCore/qglobal.h:99,
                 from /usr/include/qt5/QtGui/qtguiglobal.h:43,
                 from /usr/include/qt5/QtWidgets/qtwidgetsglobal.h:43,
                 from /usr/include/qt5/QtWidgets/qapplication.h:43,
                 from /usr/include/qt5/QtWidgets/QApplication:1,
                 from dbusadaptor.cpp:50:
dbusadaptor.cpp:175:5: error: expected unqualified-id before end of line
     Q_OBJECT
     ^~~~~~~~
dbusadaptor.cpp:175:5: error: expected declaration before end of line
make: *** [Makefile:419: dbusadaptor.o] Error 1