Methods

1
Methods

• Introduced to remove repetitive pieces of code in
  your program
• Transition from sequential programming to
  structured programming
• Also known as functions

2
Example Initial Code

• public static void main(String args)
• int input1,input2 // Taken from user
• int result11, result21 // Taken from user
• .
• for(int iinput1igt1i--) result1i
• for(int jinputjgt1j--) result2j
• .

3
Example Changed Code

• public static void main(String args)
• int input1,input2 // Taken from user
• int result11, result21 // Taken from user
• .
• result1 factorial(input1)
• result2 factorial(input2)
• .

4
Method Definition

• int factorial(int in)
• int retvalue 1
• for(int i in i gt 1 i )
• retvalue i
• return retvalue

5
Methods (Contd)

• The factorial function is acting like a black
  box. Just put in the input and it would generate
  and provide the result to the main function.
• The return types and the parameters types should
  be consistent with the variables used!

6
Methods (Contd)

• It is not essential to return
• Eg
• void printName(String name)
• System.out.println(name)

7
Methods (Contd)

• Similarly, it is not necessary to put in
  parameters
• E.g
• void printHello()
• System.out.println(Hello)
• const String getConstantString()
• const String s abc return s

8
Exercise I

• Implement the following problem by using methods
  (i) Add, (ii) Factorial
• User puts in two numbers input1 and input2
• Returns add(factorial(input1)factorial(input2))

9
Solution

• public class Main
• public static void main(String args)
• int input1, input2
• int fact1, fact2
• //inputs taken from user through console
• fact1 factorial(input1)
• fact2 factorial(input2)
• System.out.println(Add(fact1, fact2))

10
Solution (Contd)

• public static int factorial(int in)
• int result 1
• for(int i 1 i lt in i)
• result i
• return result

11
Solution (Contd)

• public static int Add(int a, int b)
• int r a b
• return r
• // Closing brace of class Main

12
Bonus Exercise II

• Implement an add function between 2 positive
  integers. Previously you were not allowed to use
  the binary operators This time you are NOT EVEN
  allowed to use any kind of loops
• Hint Try using the add function within the add
  function (recursive function)