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From: Eric Sosman <esosman@comcast-dot-net.invalid>
Newsgroups: comp.lang.java.programmer
Subject: Re: How to write constructor for an abstarct class?
Date: Mon, 28 Dec 2015 08:21:08 -0500
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On 12/28/2015 7:44 AM, Xue Feng wrote:
> I have written a Shape class to test abstract class. My plan is to
> include two fields x and y to represent the coordinate of a shape, and
> add two constructors to initialize the coordinate. In addition, two
> abstract methods, namely getArea() and getPerimeter(), is included to
> calculate the area and perimeter of a shape respectively. The two
> methods will be overrided by subclass of Shape. The code is as follows:
>
> class Shape {
>      int x, y;
>
>      public Shape(int x, int y) {
>          this.x = x;
>          this.y = y;
>      }
>
>      public Shape() {
>          this(0, 0);
>      }
>
>      public abstract double getArea();
>      public abstract double getPerimeter();
> }
>
> While compiling, the second constructor
>
>      public Shape() {
>          this(0, 0);
>      }
>
> will cause error. I am aware of that Shape is an abstract class, hence
> can not be instantiated. But, how can I write the constructor
> alternately? Thanks.

     I see no problem with the constructor.  What is "error" you get?

     However, the code you posted has a problem: The class itself must be
declared `abstract' if it has abstract methods, as in

	abstract class Shape { ...

     Are you sure that the code you posted is the same code that gives
you trouble?

-- 
esosman@comcast-dot-net.invalid
"Don't be afraid of work. Make work afraid of you." -- TLM