Diameter, perimeter and area of a circle and length of an arc

In the article Right and distance between two points, we saw how to link two points with x and y coordinates to create a segment in Java. In this tutorial, we'll use the Point.java to draw a center circle p(x, y) and radius r. Let's start with the creation of the class Circle:

public class Point {
 double x,y; 
 public Point(double x, double y){
 this.x = x;
 this.y = y; 
 }
}

public class Circle {

 Center point; 
 double radius; 
 
 public Circle(Center Point, Double Radius){
 this.center=center; 
 this.radius=radius; 
 } 
}

Definitions

In a circle, we should know:
  • The diameter: composed of two rays, its length is 2r.
  • The arc length: is a part of the circle subtended by an alpha angle expressed in radians, is equal to alpha*r.
  • The Perimeter: is the length for an alpha angle of 2*PI, the length is 2*r*PI (PI=3.14).
  • The surface or the air of the circle: PI*r².
Radius, Diameter, Arc and Area of a Circle in Java

The following Java code implements the four methods to obtain diameter, arc length, perimeter, and area: getDiameter(), getLength(), getLengthArc(), and getSurface().

public class Circle {

 Center point; 
 static double radius; 
 
 public Circle(Center Point, Double Radius){
 this.center=center; 
 this.radius=radius; 
 }
 
 static double getDiametre(){
 return radius*2; 
 }
 
 static double getLength(){
 return 2*3.14*radius; 
 }
 
 static double getSurface(){
 return 3.14*Math.pow(radius, 2); 
 }
 
 static double getLengthArc(double alpha){
 return 3.14*alpha; 
 }
 
 public static void main(String[] args) {
 
 Circle = new Circle(new Point(0, 0), 8); 
 System.out.println("Diameter: "+Circle.getDiameter()); 
 System.out.println("Length: "+Circle.getLength()); 
 //arc length with an angle of 55 radians
 double alpha = 55; 
 System.out.println("Arc Length: "+Circle.getArcLength(55)); 
 System.out.println("Surface: "+Circle.getSurface()); 
 }
}
Output
Diameter: 16.0
Perimeter: 50.24
Arc length: 172.700000000000002
Area: 200.96