Introduction



class Circles {
double radius; 

public Circles (double r){
radius = r;
}

public double Circumference  (){
return 2 * Math.PI * radius;
}

public double Surface (){
return Math.PI * Math.pow(radius,2);
}

public void Display (String Kind){
System.out.println("\n\t The circle" + Kind + " has the following 
features: \n\t Radius = " + radius + "\n\t Circumference   
= " + Circumference () 
+ "\n\t Surface = "  + Surface ());
}

}

public class TestCircles{

public static void main (String[] args){
final int MAX = 7;
Circles [] circle = new Circles [MAX];
for (int k = 0; k <= 6; k++){
circle[k] = new Circles (k+1);
}

int NumCircles = 4;
Display (circle, NumCircles);
}

static void Display (Circles [] circle, int m){
System.out.println ("\n The features of the " + m +  " 
circles are as follows:\n");
for (int i = 0; i < m; i++)
circle [i].Display (" of index " + i);
System.out.println();
}



II. The execution gives:

 how to build an array:

ConstructorName [] ItsName = 
new ConstructorName [MaxIdex]

ConstructorName [index].Methode();



C:\Java>javac TestCircles.java
C:\Java>java TestCircles

 The features of the 4 circles are as follows:


         The circle of index 0 has the following features:
         Radius = 1.0
         Circumference   = 6.283185307179586
         Surface = 3.141592653589793

         The circle of index 1 has the following features:
         Radius = 2.0
         Circumference   = 12.566370614359172
         Surface = 12.566370614359172

         The circle of index 2 has the following features:
         Radius = 3.0
         Circumference   = 18.84955592153876
         Surface = 28.274333882308138

         The circle of index 3 has the following features:
         Radius = 4.0
         Circumference   = 25.132741228718345
         Surface = 50.26548245743669