Programming Fundamentals I CS 110, Central Washington University. November 2015

Transcription

1 Programming Fundamentals I CS 110, Central Washington University November 2015

2 Next homework, #4, was due tonight! Lab 6 is due on the 4 th of November Final project description + pseudocode are due 4th of November, tomorrow

3 Chapter 5 : sections 5.3 and 5.4

4 Poll Question review Today we have two intro speed poll questions You will be given 20 seconds to see each question The main method will be highlighted Both questions are the same, What does this program do? You will then be presented with the answer choices, and you'll have 60 seconds to answer The first question get ready

5 Poll Question review

6 Poll Question review What does the program on the previous slide do? A. Determine how much money user has in bank, print a message, set loan percentage, receive money B. Get user's bank account balance, if balance is zero, do not offer loan C. Determine how much money user has in bank, set loan percentage, withdraw money from account D. Get user's bank account balance, calculate loan percentage, and inform user of Loan Amount E. Determine how much money user has in bank, if balance more than 1000, then sent welcome gift F. Get user's bank account balance from keyboard, calculate loan percentage, inform user of Loan amount G. Get user's bank account balance from mouse clicks, calculate loan, inform user of Loan amount

7 Poll Question review The second question

8 Poll Question review

9 Poll Question review What does the program on the previous slide do? A. Determine how much money user has in bank, print a message, set loan percentage, receive money B. Get user's bank account balance, if balance is zero, do not offer loan C. Determine how much money user has in bank, set loan percentage, withdraw money from account D. Get user's bank account balance, calculate loan percentage, and inform user of Loan Amount E. Determine how much money user has in bank, if balance more than 1000, then sent welcome gift F. Get user's bank account balance from keyboard, calculate loan percentage, inform user of Loan amount G. Get user's bank account balance from mouse clicks, calculate loan, inform user of Loan amount Lesson Learned: even if you weren't able to select the correct answer, the second program was simpler to read you didn't need to concern yourself with details

10 What was at first a complicated program (running a city), has become a much simpler endeavor. AdayInTheLifeOfACity{ Finance Controller maintains checkbooks Finance Controller prints payroll checks Finance Controller acquires loan from the feds Finance Controller increase pension dollars... Parks and Rec commissioner fixes roads Parks and Rec commissioner mows the park's lawn Parks and Rec commissioner plants new trees Parks and Rec commissioner cleans city swimming pool... Education Superintendent hires 12 new teachers Education Superintendent fires 13 teachers Education Superintendent hires 2 new teachers Education Superintendent approves school lunch menu Education Superintendent cancels after school progs. Education Superintendent has nervous breakdown... Head Doctor buys a new MRI machine Head Doctor goes golfing Head Doctor performs first ever brain transplant Head Doctor discovers cure to the common cold... Judge raises taxes on people younger than 2 years old Judge repeals pharmacy medicinal marijuana licenses Judge purchases a new fake wig with weird curls Judge orders adding an 8th day to the week AdayInTheLifeOfACity{ runfinancedepartment(){... maintainparks(){... Finance Controller maintains checkbooks Finance Controller prints payroll checks Finance Controller acquires loan from the feds Finance Controller increase pension dollars... Parks and Rec commi ssioner fixes roads Parks and Rec commissioner mows the park's lawn Parks and Rec commi ssioner plants new trees Parks and Rec commi ssioner cleans city swimming poo... Education Superintendent hires 12 new teachers Education Superintendent fires 13 teachers Education Superintendent hires 2 new teachers Education Superintendent approves school lunch menu Education Superintendent cancels after school progs. Education Superintendent has nervous breakdown... Head Doctor buys a new MRI machine Head Doctor goe s golfing Head Doctor perform s first ever brain transplant Head Doctor discovers cure to the common cold... Judge raise s taxes on people younger than 2 years old Judge repeals pharmacy medicinal marijuana license s Judge purcha se s a new fake wig with weird curls Judge orders adding an 8th day to the week teachfeeddisiplinestudents(){... maintainthecityshealth(){... interpretandenforcethelaws(){...

11 You want to write a simple program that prompts the user for input (integer), and then squares the result // import statements import java.util.scanner; The Non-methods version... public class ProgramWithoutMethods { // the main routine public static void main (String[] args) { System.out.println("Hello, this program performs " + "a simple calculation"); System.out.print("Please input an integer: "); Scanner keyboard = new Scanner(System.in); int userinput = keyboard.nextint(); System.out.println("You've supplied " + userinput); System.out.println("The input to squareaval is " + userinput); int output = userinput * userinput; System.out.println("The square of userinput is: " + output); System.out.println("The final result is: " + output);

12 public static void main (String[] args) { System.out.println("Hello, this program performs " + "a simple calculation"); System.out.print("Please input an integer: "); Scanner keyboard = new Scanner(System.in); int userinput = keyboard.nextint(); System.out.println("You've supplied " + userinput); System.out.println("The input to squareaval is " + userinput); int output = userinput * userinput; System.out.println("The square of userinput is: " + output); System.out.println("The final result is: " + output); The method's header, which declares the method Goal: Simplify this program to use methods public static void main (String[] args) { displayinstructions(); Method modifiers Return type void is a java keyword: does not return Method Name Parentheses empty parentheses means does not take any arguments Body of the method Curly Brackets enclose...

13 public static void main (String[] args) { System.out.println("Hello, this program performs " + "a simple calculation"); System.out.print("Please input an integer: "); Scanner keyboard = new Scanner(System.in); int userinput = keyboard.nextint(); System.out.println("You've supplied " + userinput); System.out.println("The input to squareaval is " + userinput); int output = userinput * userinput; System.out.println("The square of userinput is: " + output); System.out.println("The final result is: " + output); public static void main (String[] args) { displayinstructions(); int userinput = getusersinput(); Method modifiers The java keyword return indicates return THIS value Curly Brackets enclose... Return type Method Name int The item being returned must be of the appropriate type: Body of the method empty parentheses means does not take any arguments

14 public static void main (String[] args) { System.out.println("Hello, this program performs " + "a simple calculation"); System.out.print("Please input an integer: "); Scanner keyboard = new Scanner(System.in); int userinput = keyboard.nextint(); System.out.println("You've supplied " + userinput); System.out.println("The input to squareaval is " + userinput); int output = userinput * userinput; System.out.println("The square of userinput is: " + output); System.out.println("The final result is: " + output); public static void main (String[] args) { displayinstructions(); int userinput = getusersinput(); These are? Method Modifiers This specifies? This is? The return type The Method Name Non-empty parentheses designate? the argument(s) that this method expects to receive Here a single argument is provided, input, of type int Values passed into a method are called arguments, and/or parameters

15 public static void main (String[] args) { System.out.println("Hello, this program performs " + "a simple calculation"); System.out.print("Please input an integer: "); Scanner keyboard = new Scanner(System.in); int userinput = keyboard.nextint(); System.out.println("You've supplied " + userinput); System.out.println("The input to squareaval is " + userinput); int output = userinput * userinput; System.out.println("The square of userinput is: " + output); System.out.println("The final result is: " + output); public static void main (String[] args) { displayinstructions(); int userinput = getusersinput(); What does this method's body code block do? What is the purpose of this statement? It indicates that this method returns output, which is of type int

16 public static void main (String[] args) { System.out.println("Hello, this program performs " + "a simple calculation"); System.out.print("Please input an integer: "); Scanner keyboard = new Scanner(System.in); int userinput = keyboard.nextint(); System.out.println("You've supplied " + userinput); System.out.println("The input to squareaval is " + userinput); int output = userinput * userinput; System.out.println("The square of userinput is: " + output); System.out.println("The final result is: " + output); public static void main (String[] args) { displayinstructions(); int userinput = getusersinput(); int calculationresult = squareavalue(userinput); The variable output has been declared in the code block of the method squareavalue, so that variable is accessible only WHITHIN this code block. We say that the variable output has scope only within the code block of the method squareavalue The variable input is an argument to the method, so it is NOT declared in the body of the method, and we CANNOT declare a variable in the body of the method with the same name.

17 public static void main (String[] args) { System.out.println("Hello, this program performs " + "a simple calculation"); System.out.print("Please input an integer: "); Scanner keyboard = new Scanner(System.in); int userinput = keyboard.nextint(); System.out.println("You've supplied " + userinput); System.out.println("The input to squareaval is " + userinput); int output = userinput * userinput; System.out.println("The square of userinput is: " + output); System.out.println("The final result is: " + output); public static void main (String[] args) { displayinstructions(); int userinput = getusersinput(); int calculationresult = squareavalue(userinput); printintvalue(calculationresult);? Here, valtoprint is not declared inside of the code block because it is being passed TO the method as an argument

18 public static void main (String[] args) { System.out.println("Hello, this program performs " + "a simple calculation"); System.out.print("Please input an integer: "); Scanner keyboard = new Scanner(System.in); int userinput = keyboard.nextint(); System.out.println("You've supplied " + userinput); System.out.println("The input to squareaval is " + userinput); int output = userinput * userinput; System.out.println("The square of userinput is: " + output); System.out.println("The final result is: " + output); public static void main (String[] args) { displayinstructions(); int userinput = getusersinput(); int calculationresult = squareavalue(userinput); printintvalue(calculationresult); The version without methods What have we accomplished in rewriting the program? The version with methods The program with methods is easier to read The program with methods is modular, in that each method's name clearly designates what that part of the program is doing The dependency of the parts of the program (squareavalue is dependent on the user's input), is easy to see Okay fine but WHERE are the methods that's we've written?

19 // import statements import java.util.scanner; public class ProgramWithMethods { // a method that prints instructions public static void displayinstructions(){ System.out.println("Hello, this program performs a simple calculation"); // a method that queries a user for a number and returns value public static int getusersinput(){ System.out.println("Please input an integer: "); Scanner keyboard = new Scanner(System.in); int userinput = keyboard.nextint(); return userinput; // a method that performs a calculation and returns the result public static int squareavalue(int input){ int output = input * input; return output; // a method that prints a value (the argument) public static void printintvalue(int valtoprint){ System.out.println("The argument passed to printintval is: " + valtoprint); // the main routine public static void main (String[] args) { displayinstructions(); int userinput = getusersinput(); int calculationresult = squareavalue(userinput); printintvalue(calculationresult); Method that prints instructions Method that gets input from keyboard and returns it as an int Method that squares a value Method that prints a value main method

20 is where the program begins // the main routine public static void main (String[] args) { displayinstructions(); int userinput = getusersinput(); int calculationresult = squareavalue(userinput); printintvalue(calculationresult); Method call (or invocation) that returns nothing and takes no arguments Method call (or invocation) that returns an integer and takes no arguments Method call (or invocation) that returns an integer and takes an argument Method call (or invocation) that returns nothing (void) and takes an argument

21 // import statements import java.util.scanner; public class ProgramWithMethods { // a method that prints instructions public static void displayinstructions(){ System.out.println("Hello, this program performs a simple calculation"); // a method that queries a user for a number and returns value public static int getusersinput(){ System.out.println("Please input an integer: "); Scanner keyboard = new Scanner(System.in); int userinput = keyboard.nextint(); return userinput; // a method that performs a calculation and returns the result public static int squareavalue(int input){ int output = input * input; return output; // a method that prints a value (the argument) public static void printintvalue(int valtoprint){ System.out.println("The argument passed to printintval is: " + valtoprint); // the main routine public static void main (String[] args) { displayinstructions(); int userinput = getusersinput(); int calculationresult = squareavalue(userinput); printintvalue(calculationresult); When the program starts, it begins in the main method The first statement is a call to a method So the program proceeds to execute that method When that method completes... The program resumes executing that part of the main method where it was last Which is a declaration and assignment, that calls another method So the program executes that method... And a scanner is created... A new variable is declared and assigned a value taken from the keyboard And the return keyword indicates, return the value in the variable userinput Later we will learn how methods can return things other than just integers or values of variables As soon as this method completes, then the variable userinput is REMOVED from the computer's memory The variable userinput is a local variable, that is accessible ONLY to the code block where it was declared

22 // import statements import java.util.scanner; public class ProgramWithMethods { // a method that prints instructions public static void displayinstructions(){ System.out.println("Hello, this program performs a simple calculation"); // a method that queries a user for a number and returns value public static int getusersinput(){ System.out.println("Please input an integer: "); Scanner keyboard = new Scanner(System.in); int userinput = keyboard.nextint(); return userinput; // a method that performs a calculation and returns the result public static int squareavalue(int input){ int output = input * input; return output; // a method that prints a value (the argument) public static void printintvalue(int valtoprint){ System.out.println("The argument passed to printintval is: " + valtoprint); // the main routine public static void main (String[] args) { displayinstructions(); int userinput = getusersinput(); int calculationresult = squareavalue(userinput); printintvalue(calculationresult); When the program starts, it begins in the main method And the program resumes executing the main method where it left off last Which is a declaration of a variable, and an assignment, that is the output of a method that takes a single argument That method is executed, variables that have scope ONLY in that method are created... And this method returns the value stored in the variable output and the main method resumes were the program last left off which involves another method. Which includes an argument, and a single System.out.println statement... Program execution returns to the point in the main method where it was last Program terminates

23 Q: Is that s it? Are methods good only for making the code easier to read??

24 Assume you want a program that will ask a user to provide the amount that he/she has in a bank account, and then performs an interest calculations once, twice, or three times. The program without methods might look like the following: Receive input from the user Ask user if he/she wants to perform interest calculation Notice the redundant code This entire program can be rewritten using methods... import java.util.scanner; public class ANonMethodProgram { // main routine public static void main (String[] args){ // create scanner and get starting amount Scanner scan = new Scanner(System.in); double startingamount=0.0, updatedamount=0.0; System.out.print(" What is the starting bank account value? "); startingamount = scan.nextdouble(); scan.nextline(); // ask three times if user wants to compound amount System.out.println("Perform interest (3.4%) calculation? Enter y for yes, and n for no: "); if (scan.nextline().equals("y")){ updatedamount = startingamount * 1.034; System.out.println("The new accnount value is: " + updatedamount); System.out.println("Perform interest (3.4%) calculation? Enter y for yes, and n for no: "); if (scan.nextline().equals("y")){ updatedamount = updatedamount * 1.034; System.out.println("The new accnount value is: " + updatedamount); System.out.println("Perform interest (3.4%) calculation? Enter y for yes, and n for no: "); if (scan.nextline().equals("y")){ updatedamount = updatedamount * 1.034; System.out.println("The new accnount value is: " + updatedamount);

25 import java.util.scanner; public class MethodsAreGood { The method getusersinput is written once and if it is working, you can think of it as an autonomous little program that you don't have to worry about.. and maybe reuse elsewhere The method compoundinterest is written once and reused multiple times // get user's initial value of account public static double getusersinput(){ Scanner scan = new Scanner(System.in); System.out.print(" What is the starting bank account value? "); return scan.nextdouble(); // compound value public static double compoundinterest(double value){ Scanner scan = new Scanner(System.in); System.out.println("Perform interest (3.4%) calculation? Enter y for yes, and n for no: "); if (scan.nextline().equals("y")){ value = value * 1.034; System.out.println("The new account value is: " + value); return value; // main routine public static void main (String[] args){ // compound interest double accountvalue = getusersinput(); accountvalue = compoundinterest(accountvalue); accountvalue = compoundinterest(accountvalue); accountvalue = compoundinterest(accountvalue);

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27 More Methods Chapter 5 Begin Chapter 6