Introduction to Methods

• Writing methods involves creating named blocks of code.

What is a method?

• A method is a named block of code that is executed when called by its name.
• The code block runs from top to bottom.
• The code block runs until it encounters a return statement.
• The code block can also run until the end of its code block.
• Methods can be seen as a minitiature program.
• Methods take data (parameters), perform functions, and return a value.

Method Code Block

• Methods contain code that runs, and are called by name to execute their code block.
• Curly brackets define a method's code block.
• Methods can contain other code blocks, such as if statements and for loops.

Why use Methods?

• Methods are convenient because they can be called repeatedly without rewriting the code.

Method Syntax

• An example of a method is: public static void main(String[] args) { //code goes here }.
• public and static are access modifiers.
• void is the return type.
• main is the method name.
• String[] args represents the method's parameters.
• When you run a program, you are actually running a method that contains code inside a block, that runs when called.

Method Execution

• When a method is called, the program execution jumps to that method, executes it, and then returns to the main program.

Parts of a Method: Header

• The method's header declares the method with its return type, name, and parameters.
• A method's signature includes the name and parameter list.

Parts of a Method: Access Modifier

• The access modifier specifies the accessibility of the method.

Parts of a Method: Return Type

• The return type specifies the type of value the method will return.
• It represents the "answer" the method provides, and indicates the type of the answer.

Parts of a Method: Name/Identifier

• The method's name should follow variable naming conventions, be descriptive, and use camelCase. -Methods are called by name followed by parentheses.

Parts of a Method: Parameter List

• A method can have many parameters or none at all.
• Parameters are placeholder variables that store values passed by the caller.
• This is where all needed information is listed, that the method needs from the program in order to execute.

Parts of a Method: Body

• The method's body is the block of code within curly brackets that executes when the method is called.
• Methods must return a value of the specified type before the bottom curly bracket is reached, unless the return type is void.

Return Keyword

• The return keyword indicates that a method's job is done and it should return a value.
• Code after a return statement will not be executed as the method has already returned.

IsPositive method example

• Consider this method:

public static boolean isPositive(int num) {
    if (num > 0)
        return true;
}

• If the num parameter supplied is bigger than 0, it returns true
• Without an else statement, this method will not return anything without a condition being met
• To fix it:

public static boolean isPositive(int num) {
    if (num > 0)
        return true;
    else
        return false;
}

• A simplified version:

public static boolean isPositive(int num) {
   if (num > 0)
    return true;
   return false; //since nothing has returned
}

• An even more simplified version:

public static boolean isPositive(int num) {
   return num > 0;
}

More on Return Keyword

• When the return keyword is encountered the method is done
• Code after a return statement that is not inside an if statement or loop will be unreachable
• A Method must have a return statement unless it is void

Void Return Type

• Methods with a void return type do not return a value.
• Methods that has a code block will run regardless if it's void or not
• Void methods can still return, they just don't return a value
• Void methods do not explicitly require a return statement, the compiler will implicitely return

Calling Methods

• Parameter matching is neccessary when calling Methods

Calling Methods - Example

public static double avgOf2(int n1, int n2) {
    int sum = n1 + n2;
    double average = sum / 2.0;
    return average;
}

• Incorrect way to call the method: avgOf2();
• Incomplete way to call method with parameters: avgOf2(????);
• Complete way to call the method, as it needs parameters: avgOf2(91, 94);
• Assigning it to a variable with the return: double myAverage = avgOf2(91, 94);

Where to Write Methods

• Methods must be written outside of other methods.
• Methods must be written inside a class.

public class Tester
{
   public static void main(String[] args)
   {
      //main code goes here.
   }

    public static int addsOne(int a)
    {
       return a + 1;
    }
}

Benefits of Writing Methods

• Easier debugging since the code can easily be found in once place
• Less code repetition is needed when reusing the function
• Easier to read since only the method name is needed