Module Introduction; Enhanced for Loop & Making Choices

What to do today (about 60 minutes)

1. 5 min – Read “The module” below: how CI401 works, when labs are, and how it is assessed.
2. 10 min – Read “BlueJ” and “Java basics”. This is the shape of every Java program you will see this term.
3. 5 min – Read “Variables”: boxes for data, and arrays.
4. 10 min – Read “Loops” (the enhanced for loop). Click through Tracer 1.
5. 15 min – Read “Choices” (if, else, else if, switch). Click through Tracers 2, 3 and 4.
6. 8 min – Try the four “What will it print?” questions. Guess first, then reveal.
7. 7 min – Read the lab tasks, then do the 8-question quiz. Aim for 6 or more. Your answers are saved on this computer.

Do not worry if the code looks scary. The slides say it plainly: almost every word and symbol may raise a question at first, and that is normal. Focus on this week’s ideas; the rest builds up step by step.

1. The module: CI401 Introduction to Programming

What is programming? A program (also called software or an application) is a set of instructions that tells a computer what to do. Programming is writing those instructions. A programming language is the language you write them in. Programming tools help you write, compile, debug and run programs. An IDE (Integrated Development Environment) puts all those tools in one place.

Why Java? Java is a high-level, general-purpose, object-oriented language, used a lot in teaching, research and industry. The slides stress: this is a programming module that happens to use Java. The ideas carry over to other languages, including the Python you already know.

BlueJ is the IDE the module uses. It is simple, made for beginners, and it is on the lab PCs. (Eclipse and IntelliJ are there too, but all the slides use BlueJ.)

How you learn

• Lecture, 2 hours a week: Monday 16:00–18:00, Huxley 300.
• Lab, 2 hours a week, in Watts 201/202: groups 1 & 2 on Monday 11:00–13:00; groups 3 & 4 on Tuesday 15:00–17:00. Check your own group in your personal timetable on My Brighton.
• Groups 1 & 2 do the previous week’s lab (their lab is before the lecture). Groups 3 & 4 do the same week’s lab.
• Lab instructions are always at the end of the lecture slides. Each week has a project zip with the examples, the exercises and the model answers.
• The weekly lab exercises are practice. They are not directly assessed.

How you are assessed

One coursework project. You need at least 40 out of 100 to pass. The details (the Assessment Brief) are in the Assessment Information area on MyStudies, but the slides say you do not need to read it yet. The project is introduced around Week 8.

Who to ask

Module leader: Shine Shan (J.Shan@brighton.ac.uk, room C519, Cockcroft 5th floor). Lab tutors: Alexey Chernov, Karina Rodriguez Echavarria and William Wilkinson. You can ask in labs, by email, or by chat with any staff member.

From the Module Overview slides.

2. Getting started with BlueJ

This part is about using BlueJ as a tool, not about Java itself. Each week you get a new project zip; you open it the same way every time.

1. Start BlueJ from the Windows Start menu (or type BlueJ in the search bar). The first time, it is an empty grey window.
2. Download the project zip, for example enhanceForChoices.zip.
3. In BlueJ click Project → Open ZIP/JAR…, pick the zip, and open it. BlueJ unzips it into a folder with the same name, next to the zip.

The yellow boxes. When a project opens you see yellow boxes. Each yellow box is one class, and its name is the class name. You can drag the boxes around.

Compile, then run

Running a Java program takes two steps:

• Compile: right-click the class box → Compile, or click Compile in the editor window. The stripes on the box disappear when it has compiled. The Compile button on the left of the main window compiles every box at once.
• Run: right-click the class box → void main(String[] args) → OK. This is the standard way. (A second way: right-click → new HelloWorld() → OK; a red box appears bottom left; right-click it → void run().)

Editing. Double-click a box to open its code. After any change, compile again before you run. If there is a mistake, BlueJ highlights it and the box shows red cross-hatches. Fix it and compile again. The slides say: errors are not failures; they are a normal part of learning.

Duplicating. To experiment without spoiling the original: right-click the class → Duplicate… → give it a new name starting with a capital letter (for example HelloExperiment).

Workflow: open project → open class → compile → run → edit → compile again → duplicate when useful.

Code essentials (what matters to Java)

• Punctuation matters. Semicolons, commas and full stops are vital. Brackets { } ( ) [ ] and quotes " " must come in matching pairs. They can sit inside each other.
• Capital letters and spelling matter. System is not system. HelloWorld, helloworld and hello world are three different names. println (short for “print line”) must be spelt exactly like that.
• Colour does not matter. BlueJ colours the code only to help you read it.
• Layout mostly does not matter to Java, as long as you do not split words, quoted text or comments. This is a big difference from Python, where indentation is part of the language. Good layout still helps humans.
• Comments are notes for humans. Java ignores everything after // on a line.

# This is a comment in Python
print("Hello")  # a comment after code
"""Python has no true block comment;
a triple-quoted string is often used instead."""

From the Using BlueJ slides, including the “Extra Reading – Code Essentials” part.

3. Java basics: reading HelloWorld

The lecture’s first program is HelloWorld. Most of it is the “wrapping” every Java program needs. The slides say: for now, focus on the one key instruction, System.out.println("Hello World");. You do not need to understand the rest yet, but here is what each part means, so it is not a mystery.

// HelloWorld: the first Java program. It prints Hello World.

// Start the class called HelloWorld. Everything else lives inside its { }.
public class HelloWorld {

    // A method called run. It holds this program's instructions.
    public void run() {
        // The important instruction: show "Hello World" on the screen,
        // then move to a new line. The ; ends the instruction.
        System.out.println("Hello World");
    }   // this } closes run()

    // main: the method Java starts from.
    public static void main(String[] args) {
        // Make a HelloWorld object and call its run() method.
        new HelloWorld().run();
    }   // this } closes main()

}   // this } closes the class

A simple way to picture the structure (from the comments in the lab code): a class is a house, a method is a room, an instruction is an item in the room. Instructions live inside methods; methods live inside classes.

class HelloWorld:
    ...   # the class body is indented

def run():
    print("Hello World")   # indented = inside run
print("not inside run")    # back out = outside

def run():          # a function with no inputs
    print("Hello World")

run()               # call it: round brackets again

def main():
    HelloWorld().run()

if __name__ == "__main__":   # the usual Python start point
    main()

HelloWorld().run()   # make an object, call its run method

print("Hello World")

message = "Hello World"   # a str
print(type(message))     # <class 'str'>

print("Hello World")      # the end of the line ends it
print("a"); print("b")   # ; only needed to put two on one line

From the main lecture (slide 4), the HelloWorld.java comments, and the BlueJ slides.

4. Variables and types: the basics

The lecture asks you to read the short “Variables and Types – The Basics” slides first. Variables are covered properly later in the module; this is just enough for this week.

Boxes on a table. Picture some boxes. Each box has a name, a shape (size), and holds one item at a time. In programming: box = variable, shape = type, item inside = value. So each variable has a name and a type, and stores one value of that type.

// Make a box called age that holds whole numbers, and put 20 in it.
int age = 20;
// Put 25 in the same box. The old value 20 is thrown away.
age = 25;

age = 20    # Python works out the type by itself
age = 25    # replace the value

Common types (just recognise them for now)

// int: a whole number
int count = 10;
// double: a number with a decimal point
double price = 9.99;
// String: text, in double quotes
String city = "Brighton";

count = 10          # int
price = 9.99        # float
city = "Brighton"   # str

From one box to many: arrays

Sometimes you need many boxes of the same shape, joined together, like train coaches.

// An array of 3 whole numbers, kept together in the variable scores
int[] scores = {80, 75, 90};
// An array of 4 Strings, kept together in the variable cities
String[] cities = {"London", "Tokyo", "York", "Brighton"};

scores = [80, 75, 90]
cities = ["London", "Tokyo", "York", "Brighton"]

Now we can store many values. The next question is: how do we do something with every item easily? That is the enhanced for loop.

From the Variables and Types slides.

Click-through tracers

Press Next step. The highlighted line is the one Java is running. Watch the variables and the terminal change. Grey-green lines are comments; Java skips them.

What will it print?

Guess first. Write your guess down. Then open the answer.

// An array of two Strings.
String[] pets = {"cat", "dog"};
// Loop: once for each pet, stopping after the last one.
for (String pet : pets) {
    // print the pet and a space, staying on the same line
    System.out.print(pet + " ");
}
// After the loop: print a word and end the line
System.out.println("done");

// A String variable holding a place.
String place = "Hove";
// Chained if: Java checks each test in order and runs
// only the first block whose test is true.
if (place.equals("Brighton")) {
    System.out.println("Home!");
} else if (place.equals("Hove")) {
    System.out.println("Next door to home");
} else {
    System.out.println("Somewhere else");
}

// Switch on month: four months share one line,
// february has its own, everything else runs default.
switch (month) {
    case "april":
    case "june":
    case "september":
    case "november":
        System.out.println("30 days");
        break;
    case "february":
        System.out.println("28 days");
        break;
    default:
        System.out.println("31 days");
}

// room holds "kitchen".
String room = "kitchen";
// Switch on room. Look carefully at where the breaks are.
switch (room) {
    case "kitchen":
        System.out.println("Can you smell the coffee?");
    case "bedroom":
        System.out.println("Plenty of room for all your clothes.");
        break;
    default:
        System.out.println("What is this room used for?");
}

Can you smell the coffee?
Plenty of room for all your clothes.

The lab: what you will do

The lab instructions are at the end of the main lecture slides (slide 46). Your Lab Walkthrough page takes you through them click by click.

1. Download the project. Get enhanceForChoices.zip and open it in BlueJ (Project → Open ZIP/JAR…).
2. Explore the example classes. Double-click each one to read the code: HelloWorld, HelloBrighton, HelloPlaces, HomeTown, EstateAgent (and StarRating). Compile and run each to check you understand it.
3. Work on the exercises (classes starting with Ex_). Follow the instructions at the top of each file:
   • Ex_HomeTown – add an else so places that are not home say “I’ve never been there”; then add an else if to give an opinion on London.
   • Ex_EstateAgent_Switch – rewrite EstateAgent using a switch statement.
   • Ex_IfLoop_NurseryRhyme (optional) – rewrite the “10 Green Bottles” program with a loop and if statements.
4. Check solutions (optional). Model answers start with Sol_. Only look after you have tried.
5. Challenging exercise (for experienced students): Star Ratings. Change StarRating to use two arrays (hotel names and ratings) and print each hotel with its stars, using a switch without breaks. The file is called Ex_StartRating_Challenging.

Need help with BlueJ? Section 2 above, or the Using BlueJ slides.

Quiz: 8 questions

Click an answer. You find out straight away. Your answers are saved in this browser.

Score: 0 / 8 Clear my answers

Optional reading: Programming and Java background, and Java on your own PC

This is from the optional Programming and Java – Additional Background and Getting Started slides. You do not need to master it before starting the practical work. The university lab PCs already have everything installed.

Background in one minute

• Computers only understand machine language (0s and 1s). High-level languages such as Java and Python use English-like words; the code you write is called source code.
• A compiler translates source code into code the computer can run.
• Java: started at Sun Microsystems in 1991, released 1995, owned by Oracle since 2010. Its motto is “write once, run anywhere”. The module uses Java SE (Standard Edition), for desktop programs.
• JDK (Java Development Kit): the tools for writing and compiling, including the compiler javac. JRE: what you need to run Java, including ready-made libraries. JVM (Java Virtual Machine): the part that actually runs your program.
• The journey: you write .java source code → the JDK compiler makes .class bytecode → the JVM turns it into machine code on Windows, Mac or Linux. The slides say: don’t worry about this; it all happens behind the scenes.
• JDK = your feet (they do the real work); IDE = your shoes (they make it more comfortable). BlueJ is one pair of shoes.

Setting up Java on your own PC

• You need a JDK and an IDE. BlueJ 5.x includes a JDK in its installer, so normally you only install BlueJ.
• Go to bluej.org, click Download, choose your system (Windows, macOS or Linux), and run the installer. Accept the licence, keep the default settings, choose “Just me” on a personal PC, leave the shortcut and “associate .bluej files” boxes ticked, then Install and Finish. If Windows warns you: More info → Run anyway (if you trust the source).
• On a Mac: download the .dmg, drag BlueJ.app into Applications. If macOS blocks it the first time: Control-click → Open → Open.
• Only if another IDE needs one: install a JDK from Oracle’s download page, then check it worked by typing java -version in Command Prompt.
• Any trouble installing? Email any module team member or ask in the lab.

Try your first program in BlueJ (from the slides)

1. Project → New Project, name it (e.g. myProject), choose a place, OK.
2. New Class → name it HelloWorld → Class → OK.
3. Double-click the box, replace the code with the code below.
4. Click Compile. Then right-click the box → void main(String[] args) → OK.

// The class HelloWorld holds the whole program.
public class HelloWorld {
    // main: where Java starts running.
    public static void main(String[] args) {
        // Print Hello, World! and move to a new line.
        System.out.println("Hello, World!");
    }   // end of main
}   // end of the class

You should see Hello, World! in the terminal window.