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Re: How to write constructor for an abstarct class?

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On 12/28/2015 4:58 PM, Eric Douglas wrote:
> Previously an abstract class was intended for partial coding, if we
> have a class which has multiple subclasses which have at least one
> abstract method which will need different implementations in the
> subclasses and at least one concrete method which can have common
> code for all subclasses.  If everything was abstract it probably made
> more sense to begin with to make it an interface, which is what
> java.awt did with Shape.  Now that interfaces can contain the methods
> with the common code, what advantage do you get for making the
> abstract class, when as you say there is the disadvantage that you
> can never add another abstract method to it without modifying all
> subclasses?  The same would be true for the interface but you could
> always add a second interface to implement, while the subclasses can
> only extend one class.

1) There are limitations on what you can do with default methods in
    interfaces - actually rather strict limitations. So often it is not
    possible to just use interface and default methods.

2) But even if it is possible then it is not necessarily appropriate
    to do it. Interface default methods exist to make it possible to
    add new methods to existing interfaces and keep existing classes
    implementing those interfaces compiling. As an extra bonus
    the default method may actually do the operation in a working but
    possible non-optimal way. Interface default methods does not exist
    to allow multiple implementation inheritance in Java. Use them
    for what they are intended for and not for more.

Arne

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How to write constructor for an abstarct class? Xue Feng <xf.lotus@yahoo.com> - 2015-12-28 20:44 +0800
  Re: How to write constructor for an abstarct class? Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-12-28 08:21 -0500
    Re: How to write constructor for an abstarct class? Jan Burse <janburse@fastmail.fm> - 2015-12-28 19:20 +0100
      Re: How to write constructor for an abstarct class? Jan Burse <janburse@fastmail.fm> - 2015-12-28 19:25 +0100
        Re: How to write constructor for an abstarct class? Jan Burse <janburse@fastmail.fm> - 2015-12-28 19:28 +0100
          Re: How to write constructor for an abstarct class? Lew <lewbloch@gmail.com> - 2015-12-28 10:40 -0800
          Re: How to write constructor for an abstarct class? Eric Douglas <e.d.programmer@gmail.com> - 2015-12-28 10:42 -0800
            Re: How to write constructor for an abstarct class? Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-12-28 14:29 -0500
            Re: How to write constructor for an abstarct class? j4n bur53 <janburse@fastmail.fm> - 2015-12-28 22:26 +0100
              Re: How to write constructor for an abstarct class? Eric Douglas <e.d.programmer@gmail.com> - 2015-12-28 13:37 -0800
              Re: How to write constructor for an abstarct class? j4n bur53 <janburse@fastmail.fm> - 2015-12-28 22:47 +0100
                Re: How to write constructor for an abstarct class? Eric Douglas <e.d.programmer@gmail.com> - 2015-12-28 13:58 -0800
                Re: How to write constructor for an abstarct class? j4n bur53 <janburse@fastmail.fm> - 2015-12-28 23:06 +0100
                Re: How to write constructor for an abstarct class? Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-12-28 17:43 -0500
                Re: How to write constructor for an abstarct class? Lew <lewbloch@gmail.com> - 2015-12-28 15:14 -0800
                Re: How to write constructor for an abstarct class? j4n bur53 <janburse@fastmail.fm> - 2015-12-29 15:02 +0100
                Re: How to write constructor for an abstarct class? Arne Vajhøj <arne@vajhoej.dk> - 2015-12-29 15:37 -0500
                Re: How to write constructor for an abstarct class? Arne Vajhøj <arne@vajhoej.dk> - 2015-12-29 15:28 -0500
            Re: How to write constructor for an abstarct class? Arne Vajhøj <arne@vajhoej.dk> - 2015-12-29 15:21 -0500
              Re: How to write constructor for an abstarct class? Arne Vajhøj <arne@vajhoej.dk> - 2015-12-29 15:22 -0500
  Re: How to write constructor for an abstarct class? j4n bur53 <janburse@fastmail.fm> - 2015-12-29 16:24 +0100

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