OOP – Differences between Methods and Functions

Basically there is not much difference between them (method and functions).

//Car Class
class Car {
    private String name;
    private String color;
    private int topSpeed;

    public Car(String name, String color, int topSpeed) {
        this.name = name;
        this.color = color;
        this.topSpeed = topSpeed;
    }

    public void accelerate() {
        //vooom!
    }
}

Differences

Method 

• it is always called using the object of that class in which the method is written. In other words, it is a piece of code that is called by a name that is associated with an object.
• it is implicitly passed on the object on which it was called.
• It is able to operate on data that is contained within the class (remembering that an object is an instance of a class – the class is the definition, the object is an instance of that data).

// Example of a Method
//Java
Car car = new Car ("polo", "Green", 200);
car.accelerate();

//Kotlin 
val car = Car ("polo", "Green", 200)
car.accelerate()

Function

• a function is a method which you can call without creating objects. In other words, a function is a piece of code that is called by name and is not associated with an object.
• It can be passed data to operate on (i.e. the parameters) and can optionally return data (the return value).
• All data that is passed to a function is explicitly passed.

Example of a Function
// Java Code
public class HelloWorld{
    protected void main(ArrayList<String> args){
        greet();
    }
    private void greet(){
        System.out.print("Hello World!");
    }
}

// Kotlin Code
class HelloWorld{
 fun main(args: Array<String>){
   greet()
 }
 fun greet(){
     println("Hello World!")
 }
}