// This file illustrates the cross language polymorphism using directors. // CEO class, which overrides Employee::getPosition(). class CEO extends Manager { public CEO(String name) { super(name); } public String getPosition() { return "CEO"; } } public class main { static { try { System.loadLibrary("example"); } catch (UnsatisfiedLinkError e) { System.err.println("Native code library failed to load. See the chapter on Dynamic Linking Problems in the SWIG Java documentation for help.\n" + e); System.exit(1); } } public static void main(String argv[]) { // Create an instance of our employee extension class, CEO. The calls to // getName() and getPosition() are standard, the call to getTitle() uses // the director wrappers to call CEO.getPosition. e = CEO("Alice") CEO e = new CEO("Alice"); System.out.println( e.getName() + " is a " + e.getPosition() ); System.out.println( "Just call her \"" + e.getTitle() + "\"" ); System.out.println( "----------------------" ); // Create a new EmployeeList instance. This class does not have a C++ // director wrapper, but can be used freely with other classes that do. EmployeeList list = new EmployeeList(); // EmployeeList owns its items, so we must surrender ownership of objects // we add. This involves first calling the __disown__ method to tell the // C++ director to start reference counting. We reassign the resulting // weakref.proxy to e so that no hard references remain. This can also be // done when the object is constructed, as in: e = // CEO("Alice").__disown__() // e = e.__disown__(); list.addEmployee(e); System.out.println( "----------------------" ); // Now we access the first four items in list (three are C++ objects that // EmployeeList's constructor adds, the last is our CEO). The virtual // methods of all these instances are treated the same. For items 0, 1, and // 2, both all methods resolve in C++. For item 3, our CEO, getTitle calls // getPosition which resolves in Java. The call to getPosition is // slightly different, however, from the e.getPosition() call above, since // now the object reference has been "laundered" by passing through // EmployeeList as an Employee*. Previously, Java resolved the call // immediately in CEO, but now Java thinks the object is an instance of // class Employee (actually EmployeePtr). So the call passes through the // Employee proxy class and on to the C wrappers and C++ director, // eventually ending up back at the CEO implementation of getPosition(). // The call to getTitle() for item 3 runs the C++ Employee::getTitle() // method, which in turn calls getPosition(). This virtual method call // passes down through the C++ director class to the Java implementation // in CEO. All this routing takes place transparently. System.out.println( "(position, title) for items 0-3:" ); System.out.println( " " + list.get_item(0).getPosition() + ", \"" + list.get_item(0).getTitle() + "\"" ); System.out.println( " " + list.get_item(1).getPosition() + ", \"" + list.get_item(1).getTitle() + "\"" ); System.out.println( " " + list.get_item(2).getPosition() + ", \"" + list.get_item(2).getTitle() + "\"" ); System.out.println( " " + list.get_item(3).getPosition() + ", \"" + list.get_item(3).getTitle() + "\"" ); System.out.println( "----------------------" ); // Time to delete the EmployeeList, which will delete all the Employee* // items it contains. The last item is our CEO, which gets destroyed as its // reference count goes to zero. The Java destructor runs, and is still // able to call self.getName() since the underlying C++ object still // exists. After this destructor runs the remaining C++ destructors run as // usual to destroy the object. list.delete(); System.out.println( "----------------------" ); // All done. System.out.println( "java exit" ); } }