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Last modified: September 12, 2019

In this quick tutorial, we'll illustrate how to calculate the area of a circle in Java.

We'll be using the well-known math formula: *r^2 * PI*.

Let's first create a method that will perform the calculation:

```
private void calculateArea(double radius) {
double area = radius * radius * Math.PI;
System.out.println("The area of the circle [radius = " + radius + "]: " + area);
}
```

Now we can read the command line argument and calculate the area:

```
double radius = Double.parseDouble(args[0]);
calculateArea(radius);
```

When we compile and run the program:

```
java CircleArea.java
javac CircleArea 7
```

we'll get the following output:

`The area of the circle [radius = 7.0]: 153.93804002589985`

Another way to get the radius value is to use input data from the user:

```
Scanner sc = new Scanner(System.in);
System.out.println("Please enter radius value: ");
double radius = sc.nextDouble();
calculateArea(radius);
```

The output is the same as in the previous example.

Besides calling a method to calculate the area as we saw in section 2, we can also create a class representing a circle:

```
public class Circle {
private double radius;
public Circle(double radius) {
this.radius = radius;
}
// standard getter and setter
private double calculateArea() {
return radius * radius * Math.PI;
}
public String toString() {
return "The area of the circle [radius = " + radius + "]: " + calculateArea();
}
}
```

We should note a few things. First of all, we don't save the area as a variable, since it is directly dependent on the radius, so we can calculate it easily. Secondly, the method that calculates the area is private since we use it in the *toString()* method. **The toString() method shouldn't call any of the public methods in the class since those methods could be overridden and their behavior would be different than the expected.**

We can now instantiate our Circle object:

`Circle circle = new Circle(7);`

The output will be the, of course, the same as before.

In this short and to-the-point article, we showed different ways of calculating the area of a circle using Java.

As always, complete source code can be found over on GitHub.

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