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From: Xue Feng <xf.lotus@yahoo.com>
Newsgroups: comp.lang.java.programmer
Subject: How to write constructor for an abstarct class?
Date: Mon, 28 Dec 2015 20:44:44 +0800
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Xref: csiph.com comp.lang.java.programmer:33399

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.