如何从库中调用主程序中的类？

Question

I have multiple programs that I need to write which share common functionality/resources. I am looking to see if I can put a substantial part of these programs into a library. The scenario is as below:

ProgA, ProgB and ProgC are the programs using libX.

libX has a class XYZ which will instantiate a class ABC.

ProgA, ProgB and ProgC all have different implementations of class ABC.

How do I structure my program to make this happen? I have tried to do research, but was unable to find an answer. Thanks in advance...

Answer 1

You may declare a public interface ABCInterface in your library which contains all methods neccessary for the operation of your library. Your different programs will then declare their classes ABC implementing this interface and pass the reference to your library's methods.

In case you need to instanciate the class (once or more often) inside your library you can pass reference to a factory instead of the class instance itself. The following code may give you an idea how to implement such functionality.

// Library code
interface ABCInterface {
    public int getValue();
}

interface ABCFactory {
    public ABCInterface createInstance();
}

class Library {
    public static void doWork(ABCFactory factory) {
        ABCInterface obj = factory.createInstance();
        System.out.println(obj.getValue());
    }
}


// Program code
class Program {
    class ABCImplementation implements ABCInterface {
        @Override
        public int getValue() {
            return 42;
        }
    }

    public void useLibrary() {
        Library.doWork(new ABCFactory() {
            @Override
            public ABCInterface createInstance() {
                return new ABCImplementation();
            }
        });
    }
}

Answer 2

it seems to mee like you need to create n inversion of control .
In this case, you need libX to have a pointer to an interface ABC that has all the functionality you want to have libX use, and then, progA, progB and progC will have to implement this interface.

as you start your program, you need to go to the shared library and inject the running program into the library with a known method such as:

setProgram(IMyInterface interface) { 
    this.interface = interface; 
}

this way, when you want to run your known response actions you run the this.interface.doSomething() and that 's it.

Answer 3

You'll simply have a basic library interface ABC which provides the interface which allows your XYZ class to interact with the classes A , B and C which all implement interface ABC .

public interface ABC {
    public void method1();
    public void method2();
}

Your library class then just needs a reference to an object which implements interface ABC .

public class XYZ {
    private ABC abc;
    public XYZ(ABC abc) { this.abc = abc; }
}

And then your A , B and C implementations either implement ABC or create objects which implement ABC on-the-fly.

To me, it sounds a lot like a callback scheme. Yor library needs a standard way to communicate results to the specific implementation. ABC is basically an event handler interface.