I am a beginner programmer and I don't know how parameters work in Java. So how do they work?

I am using code academy and I always get stuck when it comes to parameters. I watched their video but I didn't get it.Please help.

To begin with, it is parameter and not perimeter.

Let us take an example. We are defining a function which accepts a name as input and as an output, it returns a greeting message.

class GreetUser {
/*
 A Simple function which accepts a username as input and returns me back with a Hello message
*/
  public static String greet(String username) { // function declaration
    return "Hello, " + username;
  }

  public static void main(String[] args) {
    String greetingMessage = greet("Daniel"); // involing the function
    System.out.println(greetingMessage);
  }
}

1. The line: public static String greet(String username) is called function definition. What you pass in the brackets is/are called - parameters. It is basically some variables/data placeholders you define. In plain English it means - this a function does something and returns something, and what I defined in the brackets are the inputs of this function. The greet method here says, I am expecting an input of the type String. This is the parameter
2. There is another method in the program called main Once you understand point one, you can answer for yourself what is the type of parameter main function takes in .
3. There can be times when functions do no need an input, so you do not pass any parameter list to the function. Example:

public static void iDoNothing(){
}

4. You can see inside main() we are invoking or calling the greet function and passing some value to it since it expects one parameter. What you pass, it is technically called argument

So when you declare a function, in the brackets you give what input it expects and is called parameter
When you call the function, you pass values to the function and it is called argument

Please read more on this:

1. Java Tutorial
2. Difference between Parameter and Argument

Also, you should read the Guidelines of the forum about How to Ask a Good Question

Are you talking about parameters? Parameters are basically values or objects passed to the methods and manipulate in the methods. Sometimes methods return the values. Methods are always used when the same code is to be used again and again for different values - like if we have to calculate greater of two values -

    public static int greaterThan(int a, int b) {
    if(a > b)
        return a;
    else
        return b;
    }

a and b are only the name of the parameters, like we declare the variables and assign the values to the variables. And you can reuse the method more than one time -

    greaterThan(3,5);
    greaterThan(8,5);

And the results will be different -
5
8

I hope this explanation will help you to understand about the parameters.

Thanks