Defining a type cast in Java

Question

I want to define a type cast from an arbitrary type to a primitive data type in Java. Is it possible to define a cast from one arbitrary type to another arbitrary type?

public class Foo{
    //methods, constructor etc for this class
    ...
    //make it possible to cast an object of type Foo to an integer 
}
//example of how an object of type foo would be cast to an integer
public class Bar(){
    public static void main(String[] args){
        Foo foo1 = new Foo();
        int int1 = (int)foo1;
        System.out.println(int1+"");
    }
}

Answer 1

You can't cast it, but you can provide a conversion function:

public class Foo{
    //methods, constructor etc for this class
    ...
    public int toInt(){
        //convert to an int.
    }    
}

Bar then becomes:

public class Bar(){
    public static void main(String[] args){
        Foo foo1 = new Foo();
        int int1 = foo1.toInt();
        System.out.println(int1+"");
    }
}

Answer 2

It is not possible to convert from a class type (eg. Foo) to a primitive type directly. Instead you should define methods (eg. int asInteger() ) that return the value of a Foo object as an integer.

Answer 3

No, it's not. It wouldn't really make sense: how could a Foo become an int ?

Rather define a sequence of appropriate methods, such as:

public int toInt() { return 42; }

Typecasting between primitive types and Java types, such as between int and Integer , was not even originally part of Java.

Answer 4

class Foo must extend Number. Why would you want to do that though? why not just access an int variable inside of foo.