Methods

A method is a named group of instructions. It lets us reuse code instead of copying and pasting it.

You have already used a method:

System.out.println("Hello!");

println is the method's name. It prints a message in the terminal.

Creating a Method

This method prints a greeting:

public static void sayHello() {
  System.out.println("Hello!");
}

The code does not run until we call the method:

sayHello();

Here is a complete program:

public class Main {
  public static void main(String[] args) {
    sayHello();
    sayHello();
  }

  public static void sayHello() {
    System.out.println("Hello!");
  }
}

The program calls sayHello() twice, so it prints "Hello!" twice.

Parts of a Method

Look at the first line again:

public static void sayHello() {

• public static lets us call the method from main.
• void means the method does not give a value back.
• sayHello is the method's name.
• () holds any information that the method needs.
• {} contains the instructions that the method runs.

Method names usually start with a lowercase letter. If the name has multiple words, capitalize each new word: runIntake, stopMotor, or getSpeed.

Giving Information to a Method

We can give a method information when we call it:

public static void greet(String name) {
  System.out.println("Hello, " + name + "!");
}

String name is a parameter. It is a variable that the method can use.

When we call the method, we put a value inside the parentheses:

greet("Alex");
greet("Sam");

The output is:

Hello, Alex!
Hello, Sam!

A method can receive more than one value:

public static void printScore(String teamName, int score) {
  System.out.println(teamName + ": " + score);
}

printScore("Simbotics", 667);

The values must be in the same order as the parameters.

Returning a Value

Some methods calculate an answer and give it back to us. Use the answer's data type instead of void, then use return:

public static int add(int firstNumber, int secondNumber) {
  return firstNumber + secondNumber;
}

We can save or print the returned answer:

int answer = add(4, 7);
System.out.println(answer);

Methods can return other data types too:

public static boolean isPositive(double number) {
  return number > 0;
}

This method returns true when the number is positive and false when it is not.

Printing and returning are different

System.out.println() shows a value in the terminal. return sends a value back to the code that called the method.

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Methods help us organize code into small, reusable actions. Next, we will learn how classes and objects group actions with the information they use.