Week 1
- 1. COMPSCI 121: INTRODUCTION TO PROGRAMMING FALL 2019
- 2. WHAT ARE THE GOALS FOR TODAY’S CLASS • Introduce you to some java programming constructs. • Introduce you to problem solving techniques. • Demo: using jGRASP • Point out good programming practices. 2
- 3. LET’S PRACTICE T-P-S Think How do you learn best? (2 mins) Pair Share your thoughts with your neighbor (2 mins) Share A few insights with the class (2 mins) 3
- 4. WHY ARE WE USING JAVA? 4 ● Java is a widely used language in industry. ● Knowledge of Java is in high demand. ● It is a mature language (1995) and is frequently updated. ● Helps you learn other languages. ● Created as a “Software Engineering” language so that large programs can be more easily developed and maintained. ● It is designed to support software best practices.
- 5. WHY ARE WE USING JAVA? TIOBE Index for August 2019 https://www.tiobe.com/tiobe-index/ 5
- 7. PROGRAMMING STEPS & PATTERN 7 Best to write a little code, test it, debug (find and remove errors) if test(s) failed, or continue to write more code if the test(s) passed. Note: A computer can only execute one step at a time. Each step must be clearly defined.
- 8. PROGRAMMING STEPS All programming has this pattern: 8 Read and analyze all aspects of the problem the program is to address. Make sure you understand what the program should do- its logic. What are the inputs and outputs to the program? Write a step-by-step process, an algorithm, that will use the input to produce the expected output. Write code that will correctly implement some or all of the algorithm. Test some or all of the program: compare program output to correct output given a set of inputs. Continue to develop the program or debug if any tests did not pass.
- 9. BAKING ANALOGY • Problem: I want some banana bread. • Input: The ingredients. • Output: Warm banana bread to eat! • Test: Must be edible and must look and taste like banana bread. • Algorithm: A step-by-step plan, like a recipe, for getting from the Input to the Output. • Implementation: in this case, ME! 9
- 10. AN ALGORITHM YOU CAN ENJOY! 10 1. Preheat oven to 350 degrees F (175 degrees C). 2. Lightly grease a 9x5 inch loaf pan. 3. In a large bowl, combine flour, baking soda and salt. 4. In a separate bowl, cream together butter and brown sugar. 5. Stir in eggs and mashed bananas until well blended. 6. Stir banana mixture into flour mixture; stir just to moisten. 7. Pour batter into prepared loaf pan. 8. Bake in preheated oven for 60 to 65 minutes. 9. Bake until a toothpick inserted into center of the loaf comes out clean. 10. Let bread cool in pan for 10 minutes. 11. Turn out onto a wire rack. 12. Test the output! In this case, there is no way to partially implement the algorithm, so if the test fails, you’ll have to start over!
- 11. HOW DOES PROGRAMMING IN JAVA WORK? 1. The problem is analyzed and understood. 2. Inputs and outputs defined. 3. An algorithm is designed. 4. Then, Java code is written in one or more source code files. 5. This file is compiled and run. 6. The output is generated. 7. Tests can be run on the output. 11
- 12. DEMO IN zyBooks AND JGRASP Saving files in folders Compiling & running the Salary program (from zyBooks). Printing in single/new lines. Making/removing syntax errors. 12
- 13. PROBLEM STATEMENT & ANALYSIS Write a program that calculates the annual salary given the hourly wage. 1. What are the inputs? 2. What are the outputs? THINK - PAIR - SHARE! 13
- 14. DESIGN THE ALGORITHM Write a program that calculates the annual salary given the hourly wage. 1. What are the inputs? hourly wage 2. What are the outputs? annual salary 3. What is the algorithm (steps) for the program? THINK - PAIR - SHARE! 14
- 15. DESIGN THE ALGORITHM 3. What is the algorithm (steps) for the program? 1. Get the hourly rate (for example, from user). hourlyWage = ? 2. Calculate the annual salary: hoursPerWeek = 40, weeksPerYear = 50 annSalary = hourlyWage * hoursPerWeek * weeksPerYear 3. Print the result. 15
- 16. WRITE THE JAVA CODE - CHECK FOR ERRORS 16 Line numbers Class name Variable assignment Output statements Semi-colons DEMO IN JGRASP { } braces for scope Declare a variable Note: Code in jGRASP is color-coded
- 17. CLICKER QUESTION #1 On which line does the program start when it runs? A. On the first line of the program public class Salary B. With the main statement public static void main C. With the print statement System.out.print 17
- 18. ANSWER CLICKER QUESTION #1 On which line does the program start? A. On the first line of the program public class Salary B. With the main statement public static void main C. With the print statement System.out.print 18
- 19. HOW DO WE ASSIGN VALUES TO VARIABLES? Assignment statements: create a variable and assign a value to it. int num = 450; • LHS has to be a variable, RHS has to resolve to a value. 19 value assignment operator data type variable name RHSLHS “Declaration” of the variable “num” with data type “int”. It also assigns the value 450 to that variable.
- 20. ASSIGNMENT IN JAVA: WHAT HAPPENS IN MEMORY 20 EXAMPLE: After the execution of the last statement, the variable “num1” now references an integer value of 3. State diagram
- 21. ASSIGNMENT IN JAVA: WHAT HAPPENS IN MEMORY 21 Notice that you declare a variable only once, but can use it as much as necessary once it’s declared. You cannot re-declare a variable: int a = 450; int a = 450; int a = 22; declaration OK re-declaration Not OK You can re-assign a variable: int a = 450; a = 22; re-assignment OK
- 22. CLICKER QUESTION 2 Which variable holds the highest number? 1. int num = 14; 2. int num2 = (num + 1); 3. int num3 = num2; 4. num2 = num3 + 3; 5. num = 17; A. num B. num2 C. num3 22
- 23. ANSWER CLICKER QUESTION 2 Which variable holds the highest number? 1. int num = 14; 2. int num2 = (num + 1); 3. int num3 = num2; 4. num2 = num3 + 3; 5. num = 17; A. num = 17 B. num2 = 18 C. num3 = 15 23
- 24. HOW DID WE SHOW THE OUTPUT TO THE USER? 24 Uses "" to output a string literal. Multiple output statements continue printing on the same output line. Uses "" to output a string literal. Starts a new output line after the outputted values, called a newline.
- 25. CLICKER QUESTION 3 Given this code (assume variables have been declared): hourlyWage = 20, hoursPerWeek = 40, weeksPerYear = 50; annSalary = hourlyWage * hoursPerWeek * weeksPerYear; Which one does not print 40000? A. System.out.print(annSalary); B. System.out.print(hourlyWage * hoursPerWeek * weeksPerYear); C. System.out.print(“annSalary”); D. System.out.print(20 * 40 * 50); 25
- 26. CLICKER QUESTION 3 Given this code (assume variables have been declared): hourlyWage = 20, hoursPerWeek = 40, weeksPerYear = 50; annSalary = hourlyWage * hoursPerWeek * weeksPerYear; Which one does not print 40000? A. System.out.print(annSalary); B. System.out.print(hourlyWage * hoursPerWeek * weeksPerYear); C. System.out.print(“annSalary”); D. System.out.print(20 * 40 * 50); 26
- 27. PROBLEM: HOW DO WE GET USER INPUT FOR OUR PROGRAM? For our Salary program, we want the user to input the wage from the keyboard. Solution: we use the special Java text parser called Scanner. Steps: 1. Create a Scanner object: Scanner scnr = new Scanner(System.in); System.in corresponds to keyboard input. 2. Given Scanner object scnr, get an input value and assign to a variable with scnr.nextInt() scnr.nextInt()is a function (method) that gets the input value of type integer (int) 27
- 28. USING SCANNER TO GET USER INPUT FROM KEYBOARD 28 Import the Scanner class Create instance Scanner method
- 29. TESTING FOR LOGIC ERRORS 29 Now let’s calculate the monthly salary. What if our program works but the output is wrong?
- 30. GRADING CRITERIA OF PROGRAMMING PROJECTS Code Style: follows good style (as defined in the course material). This means your code is readable to you and to others. This is professional “best practice”. Code Compiles: A program that doesn't compile cannot run and is not a successful program. This program does not get credit. Logical Correctness: The code is logically correct if it runs and produces the correct output. 30
- 31. CLICKER QUESTION 4 A. All that glittersis not gold. B. All that glitters is not gold. C. All that glitters isnot gold. D. All that glitters is not gold. What is the output of running this file? 31
- 32. CLICKER QUESTION 4 ANSWER A. All that glittersis not gold. B. All that glitters is not gold. C. All that glitters isnot gold. D. All that glitters is not gold. What is the output of running this file? Watch white spaces! 32
- 33. SOME GOOD PROGRAMMING PRACTICES 1. Create a good solution (algorithm) first, before you start coding. 2. Compile after writing only a few lines of code, rather than writing tens of lines and then compiling. 3. Make incremental changes— Don't try to change everything at once. 4. Focus on fixing just the first error reported by the compiler, and then re-compiling. 5. When you don't find an error at a specified line, look to previous lines. 6. Be careful not type the number "1" or a capital I in System.out.println. 7. Do not type numbers directly in the output statements; use the variables. 33
- 34. Week 1 TODO List: 1. Register your iClicker in Moodle. 2. Install OpenJDK and jGRASP. 3. Complete zyBook chapter 1 exercises. 4. Attend lab on Friday with your laptop. 5. Read the course documents (Moodle). 6.Give your consent to use Gradescope. 7.Complete the Orientation Quiz in Moodle. 8.Ask questions in Piazza. 34