How to Find Area of a Circle with Diameter in Java | Functions

How to find area of a circle with diameter in Java using functions.

In this article, you will learn how to find area of a circle with diameter in Java using functions.

Example

Standard Formula

You should have knowledge of the following topics in Java programming to understand this program:

• Java java.util.Scanner package
• Java main() method
• Java System.out.println() function

1. By using the default value of PI = 3.14

// How to Find Area of a Circle with Diameter in Java
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
    	Scanner in = new Scanner(System.in);
        System.out.println("Enter the radius of the circle::\n");

        float r = in.nextFloat();
        float d;
        float c;
        float a;
        // r = radius, d = diameter, c = circumference, a = area

        // It will calculate the diameter, circumference, and area
	    d = 2 * r;
	    c = 2 * (float)3.14 * r;
	    a = (float)3.14 * (r * r);

        System.out.println("\nDiameter      = " + d + " units");
        System.out.println("Circumference = " + c + " units");
        System.out.println("Area          = " + a + " sq. units");
    }
}

Run

Output

Explanation

In the above program, we have taken input 7 from the user via the system console. Then we applied the standard formula to calculate the diameter, circumference, and area.

Standard formulas are given at the top of the article near the example portion can see there.

After the whole calculation, It will return these values following: 

• Diameter = 14.0 units
• Circumference = 43.960003 units
• Area = 153.86 sq. units

2. By using Math.PI constant

// How to Find Area of a Circle with Diameter in Java using Math.PI
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
    	Scanner in = new Scanner(System.in);
        System.out.println("Enter the radius of the circle::\n");

        float r = in.nextFloat();
        float d;
        float c;
        float a;
        // r = radius, d = diameter, c = circumference, a = area

        // It will calculate the diameter, circumference, and area
	    d = 2 * r;
	    c = (float)(2 * Math.PI * r);
	    a = (float)(Math.PI * Math.pow(r, 2));

        System.out.println("\nDiameter      = " + d + " units");
        System.out.println("Circumference = " + c + " units");
        System.out.println("Area          = " + a + " sq. units");
    }
}

Run

Output

How to Find Area of a Circle with Diameter in Java using Functions

// How to Find Area of a Circle with Diameter in Java using Functions
import java.util.Scanner;

public class Main {
    // To calculate the diameter
    public static float Diameter(float r) {
        return 2 * r;
    }
    
    // To calculate the circumference
    public static float Circumference(float r) {
        return 2 * (float)3.14 * r;
    }
    
    // To calculate the area
    public static float Area(float r) {
        return (float)3.14 * (r * r);
    }
    
    // It's the driver function
    public static void main(String[] args) {
    	Scanner in = new Scanner(System.in);
        System.out.println("Enter the radius of the circle::\n");

        float r = in.nextFloat(); // r = radius

        // It will print the final output
        System.out.println("\nDiameter      = " + Diameter(r) + " units");
        System.out.println("Circumference = " + Circumference(r) + " units");
        System.out.println("Area          = " + Area(r) + " sq. units");
    }
}

Run