In this program we will use Math.PI to use value of PI.

/* Java program to create class to calculate
area and perimeter of circle. */

import java.util.*;

class AreaOfCircle {
  private float radius = 0.0f;
  private float area = 0.0f;
  private float perimeter = 0.0f;

  //function to read radius
  public void readRadius() {
    //Scanner class - to read value from keyboard
    Scanner sc = new Scanner(System.in);
    System.out.print("Enter radius:");
    radius = sc.nextFloat(); //to read float value from keyboard
  }

  //funtction to calculate area
  //return value - will return calculated area
  public float getArea() {
    area = (float)Math.PI*radius*radius;
    return area;
  }

  //funtction to calculate perimeter
  //return value - will return calculated perimeter
  public float getPerimeter() {
    perimeter = 2 * (float)Math.PI * radius;
    return perimeter;
  }
}
public class circle {
  public static void main(String[] s) {
    AreaOfCircle area = new AreaOfCircle();

    area.readRadius();
    System.out.println("Area of circle:" + area.getArea());
    System.out.println("Perimeter of circle:" + area.getPerimeter());
  }
}

Output

Compile: javac circle.java
Run: java circle

Output:
Enter radius:15.50
Area of circle:754.385
Perimeter of circle:97.340004