Calling a base class constructor from derived class in Java

Question

I have a class as follows:

public class Polygon  extends Shape{

    private int noSides;
    private int lenghts[];

    public Polygon(int id,Point center,int noSides,int lengths[]) {
        super(id, center);
        this.noSides = noSides;
        this.lenghts = lengths;
    }
}

Now a regular polygon is a polygon whose all sides are equal. What should be the constructor of my regular polygon?

public Regularpolygon extends Polygon{

//constructor ???
}

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score 58 · Accepted Answer · edited May 26 '19 at 16:46

public class Polygon  extends Shape {    
    private int noSides;
    private int lenghts[];

    public Polygon(int id,Point center,int noSides,int lengths[]) {
        super(id, center);
        this.noSides = noSides;
        this.lenghts = lengths;
    }
}

public class RegularPolygon extends Polygon {
    private static int[] getFilledArray(int noSides, int length) {
        int[] a = new int[noSides];
        java.util.Arrays.fill(a, length);
        return a;
    }

    public RegularPolygon(int id, Point center, int noSides, int length) {
        super(id, center, noSides, getFilledArray(noSides, length));
    }
}

score 3 · Answer 2 · edited Apr 17 '13 at 09:52

3

class Foo {
    Foo(String str) { }
}

class Bar extends Foo {
    Bar(String str) {
        // Here I am explicitly calling the superclass 
        // constructor - since constructors are not inherited
        // you must chain them like this.
        super(str);
    }
}

edited Apr 17 '13 at 09:52

skuntsel

11,624
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67

answered Apr 17 '13 at 09:28

user2290013

31
1

I think the question was different. You somehow missed the point. – Olimpiu POP Apr 17 '13 at 09:49

JWhiz · Answer 3 · 2010-08-17T17:48:37.767

2

Your constructor should be

public Regularpolygon extends Polygon{

public Regularpolygon (int id,Point center,int noSides,int lengths[]){
super(id, center,noSides,lengths[]);

// YOUR CODE HERE

}

}

edited Aug 17 '10 at 17:48

answered Aug 17 '10 at 17:30

JWhiz

681
3
10
22

5

I had to -1 for the nonsense about it being good coding practice to provide a no-arg constructor in the base class. – Mark Peters Aug 17 '10 at 17:39

Calling a base class constructor from derived class in Java

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