warm-up: april 21 write a loop (type of your choosing) that prints every 3 rd number between 10 and...
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Warm-Up: April 21
• Write a loop (type of your choosing) that prints every 3rd number between 10 and 50.
User-Defined MethodsPre-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 20-30 is “ + sum);
sum=0;for (int i=35; i <= 45; i++)
sum = sum + i;System.out.println(“Sum from 35-45 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 20-30 is “ + sum);
sum=0;for (int i=35; i <= 45; i++)
sum = sum + i;System.out.println(“Sum from 35-45 is “ + sum);
Case Study – Using Methodspublic 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 20-30 is “ +
sum(20,30));System.out.println(“Sum from 35-45 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 Methodpublic static int max(int a, int b) {
if (a >= b)return a;
elsereturn 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 Methodpublic static int max(int a, int b) {
if (a >= b)return a;
elsereturn 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 Methodpublic static int max(int a, int b) {
if (a >= b)return a;
elsereturn 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 Methodpublic static int max(int a, int b) {
if (a >= b)return a;
elsereturn 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 Methodpublic static int max(int a, int b) {
if (a >= b)return a;
elsereturn 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 Methodpublic static int max(int a, int b) {
if (a >= b)return a;
elsereturn 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 Methodpublic static int max(int a, int b) {
if (a >= b)return a;
elsereturn 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 MethodsPre-AP Computer Science, Cycle 6
Methods - Reviewpublic static int max(int a, int b) {
if (a >= b)return a;
elsereturn 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!”);System.out.println(“Warmup!”);System.out.println(“Warmup!”);
}
Type II and III MethodsPre-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 Bpublic 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?
Whyint biggest = max(a,b);
and notmax(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 MethodsPre-AP Computer Science, Cycle 6
Methods - Reviewpublic static int max(int a, int b) {
if (a >= b)return a;
elsereturn 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 Numberspublic 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 Typespublic 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 Methodspublic class NAME{
public static void method1() {}
public static void method2(){}
public static void main(String[] args){}
}