Cloning an instantiated abstract class

Question

Instantiate an abstract class. -> Duplicate it, preserving the implementation of the abstract method.

    public abstract class Foo{… 

    public int myVar;

    public abstract void do();

     }//Foo

elsewhere in package:

public class Gha{ … 

    Foo testFoo = new Foo{

        @Override
        public void do(){
            Log.i("" , "this is a special Foo"); //executable process
        }//do

    }//testFoo
    …
}//Gha

Can I copy testFoo in a way that copies testFoo’s .do() method body for the new Foo?

You cannot call a method `do`. Why do you need to do this? What is the point in having two separate instances for executing the same block of code? — Paul Boddington, Apr 14 '16 at 20:13
Mind adding indentation to your code snippets? It's very hard to read. — Egor, Apr 14 '16 at 20:15
@PaulBoddington I'm using many `Foo` and they each have a different method of reacting. They are also used as instance variables, and I need to make a deep copy. — Scottie, Apr 14 '16 at 20:25
Not...really? Objects are not, in general, copyable. Without a named class, you're almost certainly out of luck. Besides, the `Foo` in your example appears stateless, so there wouldn't be any point in copying it anyway? — Louis Wasserman, Apr 14 '16 at 20:29
Related: http://stackoverflow.com/questions/19188882/can-you-clone-an-anonymous-object-java-oop — azurefrog, Apr 14 '16 at 20:29
@azurefrog Thanks, I'll edit. Wrote these snippets just to post here. The actual code uses the proper `"` — Scottie, Apr 14 '16 at 20:32
@azurefrog good catch. It's not an exact duplicate, but the difference is minor enough that I think functionally it's the same:: http://stackoverflow.com/questions/19188882/can-you-clone-an-anonymous-object-java-oop — Scottie, Apr 14 '16 at 20:36

Paul Boddington · Accepted Answer · 2016-04-14T20:57:11.640

You could use clone. The use of this method is widely discouraged, but it does work.

For example:

public abstract class Foo implements Cloneable {

    private int a;
    private String b;

    public Foo(int a, String b) {
        this.a = a;
        this.b = b;
    } 

    public abstract void run();

    public int getA() { return a; }

    public String getB() { return b; }

    @Override
    public final Foo clone() {
        try {
            return (Foo) super.clone();
        } catch (CloneNotSupportedException e) {
            throw new AssertionError(); // Can't happen
        }
    }
}

Then, you can do:

Foo original = new Foo(3, "bar") {
    @Override
    public void run() {
        System.out.println("Hello, world!");
    }
};
Foo copy = original.clone();
System.out.println(copy.getA());
System.out.println(copy.getB());
copy.run();
System.out.println(copy == original);

The output is:

3
bar
Hello, world!
false

An alternative is to use Serializable.

public abstract class Foo implements Serializable {

    private int a;
    private String b;

    public Foo(int a, String b) {
        this.a = a;
        this.b = b;
    }

    public abstract void run();

    public int getA() { return a; }

    public String getB() { return b; }

    public final Foo copy() {
        try {
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            new ObjectOutputStream(baos).writeObject(this);
            return (Foo) new ObjectInputStream(new ByteArrayInputStream(baos.toByteArray())).readObject();
        } catch (Exception e) {
            throw new AssertionError(); 
        }
    }
}

With this version, replace clone by copy and you'll get the same result.

Clone seems like a good fit. I really like your first solution. Thank you. I'll poke around to find out why it's so discouraged. I never really explored it before. — Scottie, Apr 14 '16 at 20:51
@Scottie I recommend Effective Java by Josh Bloch. There's an excellent section on `clone`. The main irritation is that `clone` is not `public`, so if you have a `List extends Cloneable>` you can't actually make a deep copy, because you can't call `clone` on the elements. It's ridiculous. — Paul Boddington, Apr 14 '16 at 20:53

zgc7009 · Answer 2 · 2016-04-14T20:56:42.947

1

You can do this...

public class TestFoo extends Foo{

    private static String TAG = TestFoo.class.getSimpleName();

    @Override
    public void do(){
        Log.i(getTag() , “this is a special Foo”); //executable process
    }

    protected String getTag(){
        return TAG;
    }
}

And then instantiate TestFoo objects that will perform do(). If you want a separate Tag for each instance you can override the getTag() function in the instanted class. Not sure if this is what you need but a lot easier to explain than a comment :P

NOTE

If this is something you would be doing in a lot of places, and you don't want to subclass all over the place (mentioned in the comments) please look at Paul Boddington's answer, particularly the copy portion.

edited Apr 14 '16 at 20:56

answered Apr 14 '16 at 20:28

zgc7009

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Yep, that would work, thank you. That's actually how it's now, but I was/ am trying to cut down on the clutter of a whole pile of sub-classed `Foo`s. – Scottie Apr 14 '16 at 20:30
@Scottie It sounds like you may want to sit down and rethink how you are working your app. If Foo get's overridden by a bunch of subclasses you should just use an interface. – zgc7009 Apr 14 '16 at 20:32
The actual `Foo` would have instance variables. I will update the question. @zgc7009 – Scottie Apr 14 '16 at 20:37
@Scottie What is the purpose of the var? If the purpose of the var is to use it in do, just pass it to do as a parameter and return whatever you need instead of void. – zgc7009 Apr 14 '16 at 20:41
I missed it on first read. Never thought to use the `getSimpleName()` . I think this solves my issue. I'll store all the method bodies in a separate resource file and call them based on a switch. Thanks so much! EDIT: actually, no it doesn't, but adding a int flag and then sending to a switch would. Thanks for putting me on the right track. ;) Still kinda awkward, but functional. – Scottie Apr 14 '16 at 20:44

Cloning an instantiated abstract class

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