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About Mary Zheng

Mary Zheng
Mary has graduated from Mechanical Engineering department at ShangHai JiaoTong University. She also holds a Master degree in Computer Science from Webster University. During her studies she has been involved with a large number of projects ranging from programming and software engineering. She works as a senior Software Engineer in the telecommunications sector where she acts as a leader and works with others to design, implement, and monitor the software solution.

Pi in Java Example

In this post, we feature a comprehensive article about Pi in Java.

1. Introduction

PI is a mathematics number defined as the circumference of any circle divided by its diameter. Java has provided the java.lang.Math class since version 1. It includes a static constant PI with value of 3.141592653589793.

/*the double value that is closer than any other to pi, the ratio of the circumference of a circle to its diameter.*/
static double PI = 3.141592653589793;

In this example, I will print out the Math.PI value and use it to calculate a circle’s circumference and area.

2. Technologies Used

The example code in this article was built and run using:

  • Java 11
  • Maven 3.3.9
  • Eclipse Oxygen
  • Junit 4.12

3. Maven Project

3.1 Dependencies

I will include Junit in the pom.xml.

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>jcg.zheng.demo</groupId>
	<artifactId>java-pi-demo</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<build>
		<sourceDirectory>src</sourceDirectory>
		<plugins>
			<plugin>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>3.8.0</version>
				<configuration>
					<release>11</release>
				</configuration>
			</plugin>
		</plugins>
	</build>
	<dependencies>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>4.12</version>
		</dependency>
	</dependencies>
</project>

3.2 Circle

In this step, I will create a Circle class which has a diameter data member and two methods:

  • calculateCircumference() – calculate a circle’s circumference by multiplying PI by its diameter.
  • calculateArea() – calculate a circle’s area by multiplying PI by the square of its radius.

Circle.java

package jcg.zheng.demo;

public class Circle {

	public Circle(double diameter) {
		super();
		this.diameter = diameter;
	}

	private double diameter;

	public double calculateCircumference() {
		return Math.PI * diameter;
	}

	public double calculateArea() {
		return Math.PI * Math.pow(diameter / 2, 2);
	}
}

3.3. Circle Test

In this step, I will create a CircleTest class to print out Math.PI value and calculate a circle’s circumference and area.

  • print_Pi_value() – prints out Math.PI value.
  • calculateCircumference() – calculates the circumference of a circle whose diameter is 10 units.
  • calculateArea() – calculates the area of a circle whose diameter is 20 units.

CircleTest.java

package jcg.zheng.demo;

import static org.junit.Assert.assertEquals;

import org.junit.Test;

public class CircleTest {

	@Test
	public void print_Pi_value() {
		System.out.println(Math.PI);
		System.out.printf("%.16f", Math.PI);
	 
		assertEquals(3.14, Math.PI, 2);
	}

	@Test
	public void calculateCircumference() {
		double diameter = 10;
		Circle c = new Circle(diameter);

		assertEquals(31.42, c.calculateCircumference(), 2);
	}
	
	@Test
	public void calculateArea() {
		double diameter = 20;
		Circle c = new Circle(diameter);

		assertEquals(314.23, c.calculateArea(), 2);
	}
}

Execute mvn test -Dtest=CircleTest and capture output here.

Output

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running jcg.zheng.demo.CircleTest
3.141592653589793
3.1415926535897930
Tests run: 3, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.126 sec

Results :

Tests run: 3, Failures: 0, Errors: 0, Skipped: 0

Note: Math.PI value is defined as 3.141592653589793.

4. Pi in Java – Summary

In this example, I demonstrate the Math.PI value and how to use it to calculate a circle’s circumference and area.

5. Download the Source Code

This example consists of a Maven project which demonstrates the Math.PI constant.

Download
You can download the full source code of this example here: Pi in Java Example
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JoeHx
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Oh, I thought you were going to calculate PI, not just use it. Useful post though, nevertheless.