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Re: Are you sure, Mr. Gosling?

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On 6/7/16 12:22 PM, Eric Douglas wrote:
> On Tuesday, June 7, 2016 at 1:10:36 PM UTC-4, Robert Klemme wrote:
>> That sounds more like a use case for clone() to me as it seems to stress
>> that the original type is preserved.  It really depends on the usage.
>
> Maybe I'm getting confused then.  I thought clone() sounded wrong because it should return an instance of that class, so if you extend the class and call super.clone it gets an instance of the base class?  If your extended class needs to return an instance of itself, which needs to copy all the same values as the super class plus a few more...
>
> example:
> public class BaseClass{
> private Obj1 obj1;
> private Obj2 obj2;
> public BaseClass(final BaseClass copyMe) {
> setObj1(copyMe.getObj1());
> setObj2(copyMe.getObj2());
> }
> public Obj1 getObj1(){
> return obj1;
> }
> public Obj2 getObj2(){
> return obj2;
> }
> public void setObj1(final Obj1 newObj){
> obj1=newObj;
> }
> public void setObj2(final Obj2 newObj){
> obj2=newObj;
> }
> }
> public class ExtendedClass extends BaseClass{
> private Obj3 obj3;
> public ExtendedClass(final ExtendedClass copyMe){
> super(copyMe);
> setObj3(copyMe.getObj3());
> }
> public Obj3 getObj3(){
> return obj3;
> }
> public void setObj3(final Obj3 newObj){
> obj3=newObj;
> }
> }
>
> How would you do the clone()?

A simple shallow clone, as provided by Object.clone(), is enough for the 
above.

public class BaseClass implements Cloneable {
   private Object obj1;
   private Object obj2;
   public Object clone() {
     try {
       return super.clone();
     } catch (CloneNotSupportedException c) {
       // Not likely.
       throw new IllegalStateException();
     }
   }
   public Object getObj1(){
     return obj1;
   }
   public Object getObj2(){
     return obj2;
   }
   public void setObj1(final Object newObj){
     obj1=newObj;
   }
   public void setObj2(final Object newObj){
     obj2=newObj;
   }
}
class ExtendedClass extends BaseClass{
   private Object obj3;
   public Object getObj3(){
     return obj3;
   }
   public void setObj3(final Object newObj){
     obj3=newObj;
   }
   public static void main(String[] args) throws
    CloneNotSupportedException {
     // Set up an example instance of each class.
     BaseClass bb=new BaseClass();
     bb.setObj1("1");
     bb.setObj2("2");
     ExtendedClass ee=new ExtendedClass();
     ee.setObj1("4");
     ee.setObj2("5");
     ee.setObj3("6");

     // Try cloning them.
     BaseClass newbie=(BaseClass)bb.clone();
     System.out.println("newbie("+newbie.getObj1()
      +","+newbie.getObj2()+")");
     ExtendedClass newie=(ExtendedClass)ee.clone();
     System.out.println("newie("+newie.getObj1()+","
      +newie.getObj2()+","+newie.getObj3()+")");
   }
}

Running ExtendedClass.main prints
newbie=(1,2)
newie=(4,5,6)

Note that while clone() is declared only in BaseClass, calling clone() 
on an instance of ExtendedClass returns an instance of ExtendedClass.

If you need obj1, obj2 and obj3 to themselves be cloned rather than just 
copied, it gets more complicated.

--Mike Amling
T2JqZWN0LmNsb25lKCkgZ2V0cyB5b3UgYSBjaGVhcCBzaGFsbG93IGNvcHku

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Re: Are you sure, Mr. Gosling? Arne Vajhøj <arne@vajhoej.dk> - 2016-06-04 15:27 -0400
  Re: Are you sure, Mr. Gosling? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-04 16:43 -0400
    Re: Are you sure, Mr. Gosling? Arne Vajhøj <arne@vajhoej.dk> - 2016-06-04 18:44 -0400
      Re: Are you sure, Mr. Gosling? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-05 08:05 -0400
        Re: Are you sure, Mr. Gosling? Arne Vajhøj <arne@vajhoej.dk> - 2016-06-05 08:31 -0400
        Re: Are you sure, Mr. Gosling? Eric Douglas <e.d.programmer@gmail.com> - 2016-06-06 05:22 -0700
          Re: Are you sure, Mr. Gosling? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-06 09:00 -0400
            Re: Are you sure, Mr. Gosling? v_borchert@despammed.com (Volker Borchert) - 2016-06-06 16:06 +0000
              Re: Are you sure, Mr. Gosling? Robert Klemme <shortcutter@googlemail.com> - 2016-06-06 22:56 +0200
                Re: Are you sure, Mr. Gosling? Eric Douglas <e.d.programmer@gmail.com> - 2016-06-07 05:08 -0700
                Re: Are you sure, Mr. Gosling? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-07 08:41 -0400
                Re: Are you sure, Mr. Gosling? Martin Gregorie <martin@address-in-sig.invalid> - 2016-06-07 13:14 +0000
                Re: Are you sure, Mr. Gosling? Eric Douglas <e.d.programmer@gmail.com> - 2016-06-07 06:30 -0700
                Re: Are you sure, Mr. Gosling? Robert Klemme <shortcutter@googlemail.com> - 2016-06-07 19:10 +0200
                Re: Are you sure, Mr. Gosling? Eric Douglas <e.d.programmer@gmail.com> - 2016-06-07 10:22 -0700
                Re: Are you sure, Mr. Gosling? Mike Amling <mamling@chaff.us> - 2016-06-07 15:31 -0500
                Re: Are you sure, Mr. Gosling? Eric Douglas <e.d.programmer@gmail.com> - 2016-06-08 06:31 -0700
                Re: Are you sure, Mr. Gosling? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-08 10:41 -0400
                Re: Are you sure, Mr. Gosling? Eric Douglas <e.d.programmer@gmail.com> - 2016-06-08 10:21 -0700
                Re: Are you sure, Mr. Gosling? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-08 14:10 -0400
                Re: Are you sure, Mr. Gosling? Robert Klemme <shortcutter@googlemail.com> - 2016-06-08 20:54 +0200
                Re: Are you sure, Mr. Gosling? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-08 16:36 -0400
                Re: Are you sure, Mr. Gosling? Robert Klemme <shortcutter@googlemail.com> - 2016-06-08 23:11 +0200
                Re: Are you sure, Mr. Gosling? Lew <lewbloch@gmail.com> - 2016-06-10 12:20 -0700
                Re: Are you sure, Mr. Gosling? Robert Klemme <shortcutter@googlemail.com> - 2016-06-14 19:10 +0200
                Re: Are you sure, Mr. Gosling? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-07 17:12 -0400
                Re: Are you sure, Mr. Gosling? Robert Klemme <shortcutter@googlemail.com> - 2016-06-07 23:25 +0200
                Re: Are you sure, Mr. Gosling? Arne Vajhøj <arne@vajhoej.dk> - 2016-06-07 17:33 -0400
          Re: Are you sure, Mr. Gosling? Arne Vajhøj <arne@vajhoej.dk> - 2016-06-06 21:18 -0400

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