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 ???
}

Answer 1

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));
    }
}

Answer 2

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);
    }
}

Answer 3

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

}

}