在反序列化对象时如何找到对象所属的正确子类？

Question

This is the scenario.

I have a java code to write Serialized objects into a .ser file, and another to read the objects from the .ser file.

The code that does the Serialization also contains the class definition as follows-

abstract class Currency implements Serializable{
    protected double value;
    abstract double getValue();
    abstract void print();
}

class Rupee extends Currency{
    Rupee(double val){
        value=val;
    }
    public double getValue(){
        return value;
    }
    public void print(){
        System.out.println("INR "+value);
    }
}

class Dollar extends Currency{
    Dollar(double val){
        value=val;
    }
    public double getValue(){
        return value;
    }
    public void print(){
        System.out.println("USD "+value);
    }
}

Now, I use a Currency reference that I can downcast to either Rupee or dollar, and I randomly generate Rupee and Dollar objects and serialize them into the .ser file.

PROBLEM is, while deserializing this in another code, how do I distinguish the object being read between dollar or rupee object, as it could be either (randomly generated). readObject() method only returns an Object type, and needs to be explicitly cast. To cast, I first need to find out which class object it is. Help me out.

Answer 1

You can use the operator instanceof to retrieve the type of the instance of a given object.

Example : if (currency instanceof Dollar) {...}