在同一方法上动态传递不同类型的对象

Question

I want to write a method which would receive different type of objects dynamically. Once I receive the dynamic object, I have logic inside method to do something based on the properties associated with that object. It would be something like below:

MainClass{
class1 obj1;//all these are pojo
class2 obj2;
class3 obj3;
method1(<dynamic_object>)
}
    method1(<dynamic_object>){
        if(dynamic_object.property 1 == true){
            callmethod2(dynamic_object.property 1)
        }
        else{
            callmethod3(dynamic_object.property 1)
        }
    }

Here dynamic_objects are of different type. How can I achieve this in Java? I do not want to use reflection here .

Answer 1

In order to recognize the type of the object you can use the instanceof operator.

 private void instanceOfMethodExample(Object object){
    if(object instanceof String)
        print("Its a String!");
    else if(object instanceof Integer)
        print("Its an Int!");
    else
        print("Its a " + object.getClass().getName()); // by calling getClass().getName() method you take the class name of the object as a String
}

Answer 2

Use the visitor pattern, In a nutshell you can have something like this:

public class Visitor {

    interface UserVisitor {
        public void visit(CarUser user1);

        public void visit(BusUser user2);
    }


    static class VehicleVisitor implements UserVisitor {

        private Car vehicle;
        private Bus bus;

        VehicleVisitor(Car vehicle, Bus bus) {
            this.vehicle = vehicle;
            this.bus = bus;
        }

        public void visit(CarUser user1) {
            user1.setCar(vehicle);
        }

        public void visit(BusUser user2) {
            user2.setBus(bus);
        }
    }

    interface UserVisitorClient {
        void accept(UserVisitor visitor);
    }

    static class CarUser implements UserVisitorClient {

        private Car car;

        public void accept(UserVisitor visitor) {
            visitor.visit(this);
        }

        public void setCar(Car car) {
            this.car = car;
        }

        public Car getCar() {
            return car;
        }
    }

    static class BusUser implements UserVisitorClient {

        private Bus bus;

        public void accept(UserVisitor visitor) {
            visitor.visit(this);
        }

        public void setBus(Bus bus) {
            this.bus = bus;
        }

        public Bus getBus() {
            return bus;
        }
    }

    static class Car {

        @Override
        public String toString() {
            return "CAR";
        }
    }
    static class Bus {

        @Override
        public String toString() {
            return "BUS";
        }
    }

    public static void main(String[] args) {
        List<UserVisitorClient> users = new ArrayList<UserVisitorClient>();
        CarUser user1 = new CarUser();
        users.add(user1);
        BusUser user2 = new BusUser();
        users.add(user2);

        for (UserVisitorClient user : users) {
            VehicleVisitor visitor = new VehicleVisitor(new Car(), new Bus());
            user.accept(visitor);
        }

        System.out.println(user1.getCar());
        System.out.println(user2.getBus());
    }
}

Which is just an example. But it shows that basically you can use this pattern to support what you're trying to accomplish.

In your code, you could have:

void method1(VisitorClient client) {
    client.accept(someVisitor);
}

This will allow you to reach o more object oriented solution, relying in polymorphism instead of reflection or instanceof.

Answer 3

The best option is to use a common interface

interface HasProperty {
   boolean isSet();
}

void method1(HasProperty object) {
     if (object.isSet())
        method2(object);
     else
        method3(object);
}

Or even better have a method to call to perform an action.

interface MethodOne {
   void method1();
}

MethodOne object = ...
object.method1(); // calls the appropriate method for this object.

Answer 4

Use superclass of all objects- " Object " and check the type of object using instanceof operator.

method1(Object obj){
if(obj instanceof dynamic_object){
    callmethod2(dynamic_object.property 1)
}
else if(obj instanceof dynamic_object2) {
    callmethod3(dynamic_object2.property 1)
}

}

Answer 5

EDIT: Given your newly posted code, you may even simply wish to use an common interface, or base class, for the dynamic objects.

Interface:

public interface CommonInterface {
    boolean isValid();
    void method1();
    void method2();
    void method3();
}

Class Example:

public Class1 implements CommonInterface {
    public boolean isValid() {
        return true;
    }

    public void method1() {
        System.out.println("Method 1");
    }

    public void method2() {
        System.out.println("Method 2");
    }

    public void method3() {
        System.out.println("Method 2");
    }
}

Code:

public void doSomethingWithCommonObjects(CommonInterface object) {
    object.method1();
    if (object.isValid()) {
        object.method2();
    } else {
        object.method3();
    }
}

Each of the dynamic objects simply need to implement the CommonInterface interface, which would enforce method1(), method2(), method3() and property1() signatures for each object to implement.

---

Previous answer details for reference:

You will either have to use Java Generics , potentially with some common interface or base class for the objects in question so that you can then call their methods.

Eg

public static <T extends Comparable<T>> T maximum(T x, T y, T z) {                      
      T max = x; // assume x is initially the largest       
      if (y.compareTo(max) > 0) {
         max = y; // y is the largest so far
      }

      if (z.compareTo(max) > 0) {
         max = z; // z is the largest now                 
      }

      return max; // returns the largest object   
   }

If, however, you require to call particular methods without knowing the interface for those methods beforehand programmatically, then you're into Reflection territory.