Warm-Up: April 21 Write a loop (type of your choosing) that prints every 3 rd number between 10 and 50.

User-Defined Methods Pre-AP Computer Science, Cycle 6

Case Study: Sum the integers between 1 and 10, 20 and 30, and 35 to 45. int sum=0; for (int i=1; i <= 10; i++) sum = sum + i; System.out.println(“Sum from 1-10 is “ + sum); sum=0; for (int i=20; i <= 30; i++) sum = sum + i; System.out.println(“Sum from is “ + sum); sum=0; for (int i=35; i <= 45; i++) sum = sum + i; System.out.println(“Sum from is “ + sum);

Case Study: Sum the integers between 1 and 10, 20 and 30, and 35 to 45. int sum=0; for (int i=1; i <= 10; i++) sum = sum + i; System.out.println(“Sum from 1-10 is “ + sum); sum=0; for (int i=20; i <= 30; i++) sum = sum + i; System.out.println(“Sum from is “ + sum); sum=0; for (int i=35; i <= 45; i++) sum = sum + i; System.out.println(“Sum from is “ + sum);

Case Study – Using Methods public static int sum(int start, int end) { int sum=0; for (int i = start; i <= end; i++) sum = sum + i; return sum; } public static void main(String[] args) { System.out.println(“Sum from 1-10 is “ + sum(1,10)); System.out.println(“Sum from is “ + sum(20,30)); System.out.println(“Sum from is “ + sum(35,45)); }

Methods Associated with classes Define what objects are capable of doing Actions Essentially any command that ends with a pair of parentheses (empty or otherwise) System.out.print() Math.max() console.nextInt()

User-Defined Methods The methods we’ve used so far have come pre- written, stored in other files called packages Usually have to import those files into our programs in order to use those pre-written methods (java.util.* to use Scanner) However, we can write our own methods! User-defined methods Examples of possibly useful methods to write Sum of integers between two numbers isPrime isEven or isOdd

Why use methods? Like loops, they help make code simpler, shorter, more efficient, and more organized Modularization!

Dissecting a Method public static int sum(int start, int end) { int sum=0; for (int i = start; i <= end; i++) sum = sum + i; return sum; }

Dissecting a Method public static int sum(int start, int end) { int sum=0; for (int i = start; i <= end; i++) sum = sum + i; return sum; } Modifier – states whether the method is public or private (for our class, ALWAYS PUBLIC STATIC)

Dissecting a Method public static int sum(int start, int end) { int sum=0; for (int i = start; i <= end; i++) sum = sum + i; return sum; } Return type – data type of the information the method will return (int, double, String, void)

Dissecting a Method public static int sum(int start, int end) { int sum=0; for (int i = start; i <= end; i++) sum = sum + i; return sum; } Name of the method – this is the name that will be used when we call the method later (use it)

Dissecting a Method public static int sum(int start, int end) { int sum=0; for (int i = start; i <= end; i++) sum = sum + i; return sum; } Parameters – list of variables that we will pass to the method for it to use in the body code (may or may not be parameters)

Dissecting a Method public static int sum(int start, int end) { int sum=0; for (int i = start; i <= end; i++) sum = sum + i; return sum; } Method body – statements associated with the method to make it perform the necessary task

Dissecting a Method public static int sum(int start, int end) { int sum=0; for (int i = start; i <= end; i++) sum = sum + i; return sum; } Method return – variable or value the method should return as its “answer”

4 Types of Methods Methods may or may not return values Methods may or may not accept parameters 4 type of methods No parameters OR returns (Type I) No parameters WITH returns (Type II) Parameters with NO returns (Type III) Parameters AND returns (Type IV)

Calling a Method Defining a method does not mean it is automatically used You must call the method within the main method in order to use it The method executes, then returns to the same spot in the main method where it was called

Calling a Method public static int max(int a, int b) { if (a >= b) return a; else return b; } public static void main(String[] args) { int num1=45; int num2=32; int biggest = max(num1, num2); System.out.println(“Biggest was “ + biggest); }

Calling a Method public static int max(int a, int b) { if (a >= b) return a; else return b; } public static void main(String[] args) { int num1=45; int num2=32; int biggest = max(num1, num2); System.out.println(“Biggest was “ + biggest); }

Calling a Method public static int max(int a, int b) { if (a >= b) return a; else return b; } public static void main(String[] args) { int num1=45; int num2=32; int biggest = max(num1, num2); System.out.println(“Biggest was “ + biggest); }

Calling a Method public static int max(int a, int b) { if (a >= b) return a; else return b; } public static void main(String[] args) { int num1=45; int num2=32; int biggest = max(num1, num2); System.out.println(“Biggest was “ + biggest); }

Calling a Method public static int max(int a, int b) { if (a >= b) return a; else return b; } public static void main(String[] args) { int num1=45; int num2=32; int biggest = max(num1, num2); System.out.println(“Biggest was “ + biggest); }

Calling a Method public static int max(int a, int b) { if (a >= b) return a; else return b; } public static void main(String[] args) { int num1=45; int num2=32; int biggest = max(num1, num2); System.out.println(“Biggest was “ + biggest); }

Calling a Method public static int max(int a, int b) { if (a >= b) return a; else return b; } public static void main(String[] args) { int num1=45; int num2=32; int biggest = max(num1, num2); System.out.println(“Biggest was “ + biggest); }

Warm-Up: April 22 If you were to write a method called “isOdd”, which determines whether a number is odd or not, What would be your parameter(s) (if any)? What would be your return (if any)?

Mastery Level: Awesome Passes ALL LEFT-OVER ML:A PASSES NOT USED FOR AN EXEMPTION FOR AN IN-CLASS OR FINAL EXAM MAY BE REDEEMED FOR EXTRA CREDIT ON ANY EXAM AT THE FOLLOWING EXCHANGE RATE: 1 PASS = 2 E.C. POINTS *Note: Exam scores may not exceed 100

Type I Methods Pre-AP Computer Science, Cycle 6

Methods - Review public static int max(int a, int b) { if (a >= b) return a; else return b; } public static void main(String[] args) { int num1=45; int num2=32; int biggest = max(num1, num2); System.out.println(“Biggest was “ + biggest); }

Parameters and Returns Parameters Information passed to the method from the main method What goes inside the parenthesis max(a,b)  a,b are parameters Returns The answer the method gives back max(a,b)  the largest would be the return isPrime(num)  true or false

Type I Methods No parameters OR returns Return type will ALWAYS be void Parenthesis will ALWAYS be empty NO return statement Used exclusively to carry out an action Output a message Perform a uniform calculation AND output the answer Uniform  numbers never change

Example – Type I Method Method that outputs a name public static void name() { System.out.println(“Rachel Alexander”); }

Example – Calling name() public static void name() { System.out.println(“Rachel Alexander”); } public static void main(String[] args) { System.out.print(“Hello “); name(); System.out.println(“Nice to meet you!”); }

Example 2 – Powers of 2 Write a method that prints the first 10 powers of 2 public static void powersOf2( ) { for (int i=1; i<=10; i++) { System.out.println(pow(2,i)); }

Warm-Up: April 24 Write a method called warmup() that prints the word “warmup” 3 times

Warm-Up: April 24 Write a method called warmup() that prints the word “warmup” 3 times public static void warmup() { System.out.println(“Warmup!”); }

Type II and III Methods Pre-AP Computer Science, Week 6

Type I Methods - Review No parameters OR returns Return type will ALWAYS be void Parenthesis will ALWAYS be empty NO return statement Used exclusively to carry out an action Output a message Perform a uniform calculation AND output the answer Uniform  numbers never change

Example – Type I Method Method that outputs a name public static void name() { System.out.println(“Rachel Alexander”); }

Type II Methods No parameters WITH returns Parenthesis will ALWAYS be empty Will ALWAYS have a return statements Return data type will match that of the return Used for uniform calculations where the answer is returned Method call MUST be set equal to a variable

Type II Method – Example A public static int getRandom() { int random = Math.random()*100; return random; } public static void main(String[] args) { int newNum = getRandom(); System.out.print(“Your new number is: “); System.out.println(newNum); }

Type II Method – Example B public static char letter() { int random = Math.random()*10; if (random < 5) return ‘a’; else return ‘b’; } public static void main(String[] args) { for (int i=0; i<50; i++) { char randLetter = letter(); System.out.println(randLetter); }

Type III Methods Parameters with NO returns Parenthesis will NOT be empty Will NOT have a return statements Return data type will ALWAYS be VOID Used for non-uniform calculations where the answer is immediately outputted Method call is NOT set equal to a variable

Type III Method – Example A public static void isOdd(int num) { if (num % 2 == 1) System.out.println(num + “ is odd.”); else System.out.println(num + “ is even.”); } public static void main(String[] args) { int num = console.nextInt(); isOdd(num); }

Type III Method – Example B public static void largest(int a, int b) { if (a >= b) System.out.println(a + “ is largest.”); else System.out.println(b + “ is largest.”); } public static void main(String[] args) { int num = console.nextInt(); int num2 = console.nextInt(); largest(num, num2); }

Warm-Up: April 25 When calling a method that returns a value, why must we set the method call equal to a variable? Why int biggest = max(a,b); and not max(a,b); ?? *When finished, turn in your warm-ups page

Announcements Test next Friday Loops Methods Last test of the school year (besides the final) Will have one more quiz

Overloaded Methods Pre-AP Computer Science, Cycle 6

Methods - Review public static int max(int a, int b) { if (a >= b) return a; else return b; } public static void main(String[] args) { int num1=45; int num2=32; int biggest = max(num1, num2); System.out.println(“Biggest was “ + biggest); }

Parameters and Returns Parameters Information passed to the method from the main method What goes inside the parenthesis max(a,b)  a,b are parameters Returns The answer the method gives back max(a,b)  the largest would be the return isPrime(num)  true or false

Overloaded Methods Occurs when you write multiple methods within the same class with the exact same name, but with different parameters Useful for situations where you may be sending different numbers of parameters, or parameters of different data types

Differing Parameter Numbers public static int average(int a, int b, int c) { return (a+b+c)/3; } public static int average(int a, int b, int c, int d) { return (a+b+c+d)/4; } public static void main(String[] args) { int a = average(14, 26, 24); int b = average(56, 63, 39, 24); System.out.println(“A: “ + a + “\nB: “ + b); }

Differing Data Types public static int max(int a, int b) { if (a >= b) return a; return b; } public static double max(double a, double b) { if (a >= b) return a; return b; } public static void main(String[] args) { int a = max(15, 78); double b = max(34.56, 23.43); System.out.println(“A: “ + a + “\nB: “ + b); }

Template for Multiple Methods public class NAME { public static void method1() { } public static void method2() { } public static void main(String[] args) { }