Question

I currently am working with a constructor which takes in of type object
I am then testing it’s type based on instanceof

Public MyClass (Object obj)
{
if(obj instanceof CusClass1){
CusClass1 myObject = (CusClass1) obj;
globalVar1 = myObject.getAttrib1();
globaVar2 = myObject.getAttrib2();
}
if(obj instanceof CusClass2){
CusClass2 myObject = (CusClass2) obj;
globalVar1 = myObject.getAttrib1();
globaVar2 = myObject.getAttrib2();
}
}

Can this be offset to an initalise method called from within the constructor. The major problem is in the casting of the Object. I was always under the impression that repeated code is bad code. Can this be made more elegant?

Answer 1

A much better, more type-safe design would be to create multiple overloaded constructors. You would then not need any casts, and you would make it impossible to construct an object by passing it an object of an inappropriate type.

public MyClass(CusClass1 myObject) {
    globalVar1 = myObject.getAttrib1();
    globalVar2 = myObject.getAttrib2();
}

public MyClass(CusClass2 myObject) {
    globalVar1 = myObject.getAttrib1();
    globalVar2 = myObject.getAttrib2();
}

Do CusClass1 and CusClass2 have the same getAttrib1() and getAttrib2() methods? Then consider creating an interface that both these classes implement, and create a constructor that takes an object that implements that interface:

public interface Attribs {
    String getAttrib1();
    int getAttrib2();
}

public class CusClass1 implements Attribs {
    // ...
}

public class CusClass2 implements Attribs {
    // ...
}

public class MyClass {
    // You can now pass anything that implements interface Attribs
    public MyClass(Attribs myObject) {
        globalVar1 = myObject.getAttrib1();
        globalVar2 = myObject.getAttrib2();
    }
}