Week 1L - Lecture

How do you learn?¶

Weekw 1: Getting Started with Programming¶

Programs are written as High-Level Language Source code
- Procedural source code consists of:
  - Statements: System.out.println("Hello world");
  - Expressions: int a = 2;
  - Executed from Top-to-Bottom, Left-to-Right
- HLL were created to make coding faster and more human-readable.
- Hundres of languages, but Java is very popular and makes learning other languages easier.
- Languages like Java have many APIs, Libraries, and GUI tools to make development easier.
Modern programming is always done in an IDE
- Useful tools for programmer
  - Real-time Syntax checking
  - Auto-Documentation tools
  - Code Completion
  - Console
  - Debugger
  - AI Generative code assistance

Exercise 1 - Get familiar with IDE¶

Open your IDE, start a NEW Project
Add or find the Main.java file created for the project, what do you think the following do?
Note the line public class Main
Note the main method inside that Main.java file.
Note any // lines.
Note the ; terminating each code line.
Now locate the following.
- Build/Run Buttons
- Project/Settings
- SDK/System settings
- Console
Keep a lookout for Syntax errors/warnings in IDE

Exercise 2 - What does the following program print¶

Exercise2.java
public class Exercise2 {
    public static void main(String[] args) {
        // The statements used by the program start below!
        System.out.println("Welcome to CIS-12 - you will learn to program!");
    }
}

Simple Printing¶

Stdin, Stdout, Stderr
Java’s System.out.println(""); will output stdout to console!

Anatomy of a Java Program¶

Week1.java
public class Week1 {
    public static void main(String[] args) {
        // The statements used by the program start below!
        System.out.println("I have something to say!");
    }
}

Every java file must be named the same as the class with a .java extension.
Execution always starts in main method.
Code blocks are contained within { and } brackets.
Single line comments are denoted with //
- This is one way to document your code and leave yourself notes.

Exercise 3 - My First Print¶

YourNameHere.java
public class YourNameHere {
    public static void main(String[] args) {
        // Write a program that prints your first and last name here.
    }
}

Run the program via Build/Run
Run the program command line.
sout

Multiple Line Printing¶

You could simply put multiple print statements.

MultipleLinePrint.java
public class MultipleLinePrint {
    public static void main(String[] args) {
        System.out.println("Hello world!");
        System.out.println("Hello universe!");
        System.out.println("Hello world!\nHello universe!");
        System.out.println("""
            Hello world!
            Hello universe!
        """);
    }
}

A Glance Into Your Future¶

What is System.out.println() Really?¶

System is a static class.
out is a class/static object (e.g. only one instance for the whole system Stdout!).
println is a method in the out object that can be called via “.” because out is an object.
“Text to be printed…” is a parameter of data-type String
- A parameter is data passed to a method so the method can use it and is always in the ( ) parenthesis.
; Separates the statements and expressions in your source code.

Comments¶

So far we’ve seen single line comments //
There is also a multi-line comment:
Multi-Line Comment
1 2 3 4 5 6
/* Comment text goes here. */

Reading Input¶

What is input?¶

Remember Stdin?
It is text typed by a user that is always read as a String
There are many ways to read input, but we’ll mostly use the Scanner class.

Excercise 4 - Guess What?¶

ScannerIntro.java
import java.util.Scanner;

public class ScannerIntro {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Write Something: ");
        String message = scanner.nextLine();
        System.out.println(message);
    }
}

What it does, in human… Statement exec line-by-line¶

Introduce the scanner tool used for reading user input
Create a tool for reading user input and name it scanner
Print “Write Something: “
Read the string written by the user, and assign it
to program memory “String message = (string that was given as input)”
Print the message written by the user

What it does, in programmer…¶

Imports the Scanner class from the Java SDK libraries
Creates a Java Object of type Scanner so we can access its method for reading input.
Prints to StdOut a message requesting input
Uses “dot” notation to call the scanner object’s nextLine method to read from StdIn until a newline (i.e. \n) is encountered.
Assigns the returned typed line captured in method nextLine and stores it in variable message, which is of data-type String
Prints to StdOut the typed message out of the variable message.

Exercise 5 - User Input¶

Exercise5.java
import java.util.Scanner;

public class Exercise5 {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("Write a message: ");
        // Write a program that asks the user to write a string.
        // When the user has typed a string and pressed the enter key,
        // the program should print the string that was provided by the user.
    }
}

What is a String Anyway?¶

Why do we say String where most people would say Text?
String is just shorthand for saying charachters strung together like beads on a necklace.
- And that’s how a computer views text
We’ve used strings in printing to StdOut and reading from StdIn to store the string in a variable
So what’s a variable (Don’t worry, we’ll revisit this)!
- A storage location for some type of data (So far we’ve only seen String)
- They are declared like so String message = "Hello";
  - String is the type
  - message is the variable name
  - = is an assignment operator just like MATH!
    - It assigns the String “Hello” to the storage/memory location pointed to by message**.
- Variables are used to reference the data at their storage location throughout a program.
- Varaibles are used for Re-Use and repetition.

String Operations¶

Can we join strings together?

YES, through concatenation…

ConcatStr.java
public class ConcatStr {

    public static void main(String[] args) {
        System.out.println("Hello " + "world!");
    }
}

You can also use variables, and you can do it any number of times!

ConcatStr.java
public class ConcatStr {

    public static void main(String[] args) {
        String message1 = "Hello world!";
        String message2 = "and the universe!";

        System.out.println(message1 + " ... and the galaxy ... " + message2);
    }
}

Exercise 6 - String Concatenation¶

Bond.java
public class Bond {

    public static void main(String[] args) {
        String start = "My name is ";
        String end = ", James Bond";

        // Modify the program so that it prints the contents of the variable start and end, and the printed text is the following: My name is Bond, James Bond
    }
}

Reading Strings¶

ReadingStrings.java
//Introduce the Scanner tool used for reading
import java.util.Scanner;

public class ReadingStrings {

    public static void main(String[] args) {

        //Create the tool for reading, assign it to variable caller "scanner
        Scanner scanner = new Scanner(System.in);

        //Print user a message "Write a message: "
        System.out.println("Write a message: ");

        // nextLine method reads the user's input and returns a string
        // If we then want to use the string in the program, it must be saved to a string variable
        String message = scanner.nextLine();

        // A value saved to a variable can be used repeatedly
        System.out.println(message);
        System.out.println(message);
    }
}

Exercise 7¶

TimesThree.java
import java.util.Scanner;

public class TimesThree {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("Write a message: ");
        // Write a program that asks the user to type a string.
        // When the user has typed a string and pressed enter,
        // the program must print the user's string three times.
    }
}

Exercise 8¶

LiteralConcatenation.java
import java.util.Scanner;

public class LiteralConcatenation {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Write a program that prompts the user for their name with the message "What's your name?".
        // When the user has written their name, the program has to print "Hi "
        // followed by the user's name.
    }
}

Waiting for Input¶

What does the nextLine method really due?

Puts process thread into a wait state that will get notified asynchronously, via an event, when the enter key on the keyboard is pressed.

So what does this mean? Take the following program for example:

Program.java
import java.util.Scanner;

public class Program {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("Write the first string:");
        String first = scanner.nextLine();
        System.out.println("Write the second string:");
        String second = scanner.nextLine();
        System.out.println("Write the third string:");
        String third = scanner.nextLine();

        System.out.println("You wrote:");
        System.out.println(first);
        System.out.println(second);
        System.out.println(third);
    }
}

Thie program will pause and go idle at each call of nextLine, its context will be switched out (Think 0% CPU usage).
Upon a Keyboard Enter key being pressed, an event will be generated that will context switch it back.

Excercise 9¶

Write a program that asks the user for a name and a job to do. Your program then prints a short story as follows:

I will tell you a story, but first, I need some info!
What is your name? Trevor
What is their job? developer
Here is the story:
Once upon a time there was Trevor, who was a developer.
On the way to work, Trevor reflected on AI.
Perhaps Trevor will not be a developer forever.