CS1101: Programming Methodology

Week 2: Java Basics  Last week:  Introduction  Writing algorithms (pseudo-codes)  This week:  Chapter 1: Intro to OOP and Software Development  Chapter 2: Getting Started with Java  DrJava  CourseMarker  Next week:  Chapter 3: Numerical Data  Chapter 4: Defining Your Own Classes – Part 1 © CS1101 (AY Semester 1)Week2 - 2

Reminder  Have you read the relevant chapters and PowerPoint files BEFORE coming to this lecture? © CS1101 (AY Semester 1)Week2 - 3

Chapter 1 Intro to OOP and S/W Dev Let’s go to Chapter 1. © CS1101 (AY Semester 1)Week2 - 4

Chapter 2 Getting Started with Java Let’s go to Chapter 2. We will skip the Date and SimpleDateFormat classes. © CS1101 (AY Semester 1)Week2 - 5

Example on String methods (1/2) © CS1101 (AY Semester 1)Week2 - 6 /* Program to test out some String methods in Chapter 2 File: Ch2TestString.java */ class Ch2TestString { public static void main (String[] args) { String text = "I'm studying CS1101."; //or String text = new String("I'm studying CS1101."); //We’ll explain the difference next time. System.out.print("text: " + text); int length = text.length(); System.out.println("text.length(): " + length);

Example on String methods (2/2) © CS1101 (AY Semester 1)Week2 - 7 System.out.println("text.substring(5,8): " + text.substring(5,8)); System.out.println("text.indexOf(\"in\"): " + text.indexOf("in")); // why are there 2 backslashes (\) above? String newText = text + "How about you?"; System.out.print("newText: " + newText); } Download this program from the CS1101 website (“Resources – Lectures”). What is the output of this program?

CourseMarker (CM) You are going to use CourseMarker (CM) for submitting your lab assignments.  Password already ed to you Refer to the following:  CourseMarker website  “Using CourseMarker” PowerPoint file Available on CS1101 website © CS1101 (AY Semester 1)Week2 - 8

Example: Initials This problem is given in the Chapter 2 PowerPoint file, but the program uses JOptionPane class for input. We prefer to use the standard input (Scanner class) and show it here. Problem statement: Write a program that asks for the user’s first, middle, and last names and replies with their initials. © CS1101 (AY Semester 1)Week2 - 9 Example: input:Andrew Lloyd Weber output: ALW

Initials: Overall Plan Identify the major tasks the program has to perform  We need to know what to develop before we develop! Tasks:  Get the user’s first, middle, and last names  Extract the first letter from each name and create the initials  Output the initials © CS1101 (AY Semester 1)Week2 - 10

Initials: Development Steps We will develop this program in two steps: 1.Start with the program template and add code to get input 2.Add code to compute and display the initials © CS1101 (AY Semester 1)Week2 - 11

Initials: Step 1 Design The program specification states “get the user’s name” but doesn’t say how. We will consider “how” in the Step 1 design. We will use standard input (Scanner class) for input. We have two choices for input style:  Choice 1: Input first, middle and last names separately  Choice 2: Input the full name at once We choose choice 2 because it is easier and quicker for the user to enter the information. © CS1101 (AY Semester 1)Week2 - 12

Initials: Step 1 Code © CS1101 (AY Semester 1)Week /* Chapter 2 Sample Program: Displays the Initials File: Ch2Initials.java */ import java.util.*; class Ch2Initials { public static void main (String[] args) { Scanner scanner = new Scanner(System.in); System.out.print("Enter your full name " + " (first, middle, last): "); String name = scanner.nextLine(); System.out.println("Full name entered: " + name); } Download this program from the CS1101 website. What is the output of this program?

Initials: Step 1 Test In the testing phase, we run the program and verify that…  we can enter the name  the name we enter is displayed correctly Question:  What if we had used scanner.next() instead of scanner.nextLine()? Test it out! © CS1101 (AY Semester 1)Week2 - 14

Initials: Step 2 Design Our programming skills are limited, so we will make the following assumptions:  input string contains first, middle, and last names  first, middle, and last names are separated by single blank spaces Examples: John Quincy Adams(okay) John Kennedy(not okay) Harrison,William Henry(not okay) © CS1101 (AY Semester 1)Week2 - 15

Initials: Step 2 Design (cont’d) Given a valid input, we can generate the initials by  breaking the input name into first, middle and last  extracting the first character from each of them  concatenating the three first characters © CS1101 (AY Semester 1)Week “Aaron Ben Cosner” “Aaron” “Ben Cosner” “Ben” “Cosner” “ABC”

Initials: Step 2 Code © CS1101 (AY Semester 1)Week /* Chapter 2 Sample Program: Displays the Initials File: Ch2Initials.java */ import java.util.*; class Ch2Initials { public static void main (String[] args) { Scanner scanner = new Scanner(System.in); System.out.print("Enter your full name " + " (first, middle, last): "); String name = scanner.nextLine(); String space = " ";

Initials: Step 2 Code (cont’d) © CS1101 (AY Semester 1)Week String first = name.substring(0, name.indexOf(space)); name = name.substring(name.indexOf(space)+1, name.length()); String mid = name.substring(0, name.indexOf(space)); String last = name.substring(name.indexOf(space)+1, name.length()); // Compute the initials String initials = first.substring(0,1) + mid.substring(0,1) + last.substring(0,1); // Output the initials System.out.println("Your initials: " + initials); }

Initials: Step 2 Test In the testing phase, we run the program and verify that, for all valid input values, correct initials are displayed. We run the program numerous times. Seeing one correct answer is not enough. We have to try out many different types of (valid) input values. © CS1101 (AY Semester 1)Week2 - 19

Initials: Program Review The work of a programmer is not done yet. Once the working program is developed, we perform a critical review and see if there are any missing features or possible improvements. One possible improvement  Improve the initial prompt so the user knows the valid input format requires single spaces between the first, middle and last names. © CS1101 (AY Semester 1)Week2 - 20

Summary for Today You should have learned how to use the following:  DrJava  CourseMarker Basic Java features Some standard (built-in) classes  String  Scanner © CS1101 (AY Semester 1)Week2 - 21

Announcements/Things-to-do (1/2) CM password  Already ed to nus.edu.sg Trial Lab  Released on 15 August 2009, Saturday.  Read Module website, “CA – Labs”.  No hard deadline, but try to submit by the end of this week to ensure that you know how to use CM. © CS1101 (AY Semester 1)Week2 - 22

Announcements/Things-to-do (2/2) To prepare for next week’s lecture:  Read Chapters 3 and 4 and their PowerPoint files before you come for lecture. To prepare for next week’s discussion session:  Download “week3_discussion_qns.pdf” from module website, “CA – Discussion”.  Do the questions before you attend your discussion session. © CS1101 (AY Semester 1)Week2 - 23

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