CODEWITHSUNDEEP
javaarraysoopobject
RADXack
RADXack

Reputation: 1092

Storing References to Objects of Different Classes

I currently have two classes that I create objects from. I need an array that will store references (pointers) to these objects. Of what type should the array be?

ArrayList<Class1> visableObjs = new ArrayList<Class1>();

Will of course only store pointers to objects that stem from Class1. If I had an object from Class2 could I store it's pointer in the same array?

Upvotes: 0

Views: 1216

Answers (3)

Paul
Paul

Reputation: 3058

You could perhaps use generics to create a Choice class to hold a reference to one or other type, but not both:

public final class Choice<A,B> {

    private final A a;
    private final B b;
    private final boolean isA;

    private Choice(A a, B b, boolean isA) {
        this.a = a; this.b = b; this.isA = isA;
    }

    public static <A,B> Choice<A,B> ofA(A a) {
        return new Choice<>(a, null, true);
    }
    public static <A,B> Choice<A,B> ofB(B b) {
        return new Choice<>(null, b, false);
    }

    public boolean isA() { return isA; }
    public A getA() {
       if(!isA) throw new IllegalStateException("Not a!");
       return a;
    }

    public boolean isB() { return !isA; }
    public B getB() {
       if(isA) throw new IllegalStateException("Not b!");
       return b;
    }

    // Purely for demo purposes...
    public static void main(String[] args) {
        Choice<Integer,String> ich = Choice.ofA(42);
        Choice<Integer,String> sch = Choice.ofB("foo");
        // This is why the isA is included; so we can tell a null A from a null B.
        Choice<Integer,String> nil = Choice.ofA(null);
        //
        List<Choice<Boolean,String>> xs = new ArrayList<Choice<Boolean,String>>();
        xs.add(Choice.ofA(true));
        xs.add(Choice.ofB("neep"));
    }

}

This should work for two unrelated classes. Or for two out of many related subclasses, where you want to restrict to only those two possibilities - and not any subclass of a more general class/interface.

Such a class should probably be extended to properly implement equals()/hashCode(), toString(), etc. (For some definition [documented] of 'properly'.)

Caveat: this may not compile first try - I don't have a javac handy to test it. But the idea should be clear.

Upvotes: 0

Voidpaw
Voidpaw

Reputation: 920

if you mean that the objects you store are instances of those two classes, you should make those classes inherit from a (custom?) class or interface and use that class/interface as the type to store in your array.

Upvotes: 1

Prabhakaran Ramaswamy
Prabhakaran Ramaswamy

Reputation: 26094

We can do like this. Its not good practice at all if objects are from different classes.

ArrayList<Object> visableObjs = new ArrayList<Object>();

or

ArrayList visableObjs = new ArrayList();

Upvotes: 0

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