Java Methods - datacouch-io/spark-java GitHub Wiki

In Java, a method is a block of code that only runs when it is called. Methods can receive data, known as parameters, and they are commonly referred to as functions.

Creating a Method

To create a method, it must be declared within a class and defined with a name followed by parentheses ():

public class MyClass {
  static void myMethod() {
    // Code to be executed
  }
}

In this example:

• myMethod() is the method's name.
• static indicates that the method belongs to the MyClass class rather than an instance of MyClass. You'll learn more about objects and accessing methods through objects later.
• void means that this method does not return a value. We'll cover return values later in this chapter.

Calling a Method

To call a method in Java, you write the method's name followed by two parentheses () and a semicolon. Here's an example using the myMethod():

public class MyClass {
  static void myMethod() {
    System.out.println("I just got executed!");
  }

  public static void main(String[] args) {
    myMethod(); // Call the myMethod() method inside main
  }
}

// Outputs "I just got executed!"

Method Parameters

Methods can receive information in the form of parameters, which are specified after the method name within parentheses. You can include as many parameters as needed, separated by commas. Here's an example of a method that takes a String parameter called fname:

public class MyClass {
  static void myMethod(String fname) {
    System.out.println(fname + " Shao");
  }

  public static void main(String[] args) {
    myMethod("Jesse");
    myMethod("Larry");
    myMethod("Anja");
  }
}

// Outputs:
// Jesse Shao
// Larry Shao
// Anja Shao

Return Values

The void keyword, as used in the previous examples, indicates that the method does not return a value. If you want a method to return a value, you can specify a primitive data type (such as int, char, etc.) instead of void and use the return keyword inside the method:

public class MyClass {
  static int myMethod(int x) {
    return 5 + x;
  }

  public static void main(String[] args) {
    System.out.println(myMethod(3));
  }
}

// Outputs 8 (5 + 3)

You can also store the result in a variable:

public class MyClass {
  static int myMethod(int x, int y) {
    return x + y;
  }

  public static void main(String[] args) {
    int z = myMethod(5, 3);
    System.out.println(z);
  }
}

// Outputs 8 (5 + 3)

Methods with Conditional Statements

It is common to use conditional statements like if...else inside methods to control the flow of execution:

public class MyClass {

  static void checkAge(int age) {
    if (age < 18) {
      System.out.println("Access denied - You are not old enough!"); 
    } else {
      System.out.println("Access granted - You are old enough!"); 
    }
  } 

  public static void main(String[] args) { 
    checkAge(20); // Call the checkAge method and pass an age of 20
  } 
}

// Outputs "Access granted - You are old enough!"