> For the complete documentation index, see [llms.txt](https://codehs.gitbook.io/apjava/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://codehs.gitbook.io/apjava/classes-and-object-oriented-programming/writing-classes-and-instance-methods.md).

# Writing Classes and Instance Methods

 ***Instance methods*** allow us to define the behavior of an object. \
 Lets say you are wanting to get the area of a specific rectangle object you created using the `Rectangle` class. To do this, you would need to define an ***instance method*** that will return the area of our rectangle object. It is important to remember that ***instance methods*** belong to the specific instance of your object.

## Creating Instance Methods

The general form of an instance method is as follows:

```java
[visability] [returnType] name(parameters)
  public       double    getArea()
  private       int      truncateArea()
```

The ***visibility*** of your method determines if it can be used outside your object's class. This is usually *public* or *private*.

The ***returnType*** is the type of our return value. If there is no return value for the method we use *void*.

The ***name*** is the name of our method.

The ***parameters*** is the list of our parameters, or the information we give to the method.

Here is what our `Rectangle` class looks like:

```java
public class Rectangle
{
    // Instance variables
    private double width;
    private double height;

    public Rectangle(double rWidth, double rHeight)
    {
        width = rWidth;
        height = rHeight;
    }

    // Our instance method
    public double getArea()
    {
        return width * height;
    }
}
```

## Using Instance Methods

To call instance methods we use the following format: `objectName.methodName(parameters);` \
 \
 The ***objectName*** is the name of the object we are calling the method on. \
 The ***methodName*** is the name of the instance method we are calling. \
 The ***parameters*** are the inputs we give the method (if any).

In practice, this looks like:

```java
Rectangle rect = new Rectangle(7, 10);

// Get the area of our rectangle by calling instance method `area();`
double rectArea = rect.getArea();
```