Why Programming?

Intro

This is an introduction to Java and CS Awesome’s curriculum. It includes a video discussing the basics of Java & some activities CS Awesome uses to teach.

• Java is used in many places
  • Used widely in the development of Android apps
    • AppInventor translates it’s code into Java
  • The language used to write Minecraft
  • Used by Netflix

// All programs start with "public class" and a class name
public class MyClass {
    // Class body
    // Classes usually have a "main" method; always looks like that ↓
    public static void main(String[] args) {
        // Write your code here (this will be executed automatically)

        System.out.print("No newline here!");  // Prints out string literal given
        System.out.println("This one has it though :)"); // Same as print, but this time it ends with a line break

        System.out.println("Welcome to sloshyyy.github.io!");
    }
}

• All keywords are in lower case
  • public, static, void, etc.
• Classes are upper case
  • MyClass, System, String
• Java is case sensitive!!!
  • System != system
    • If you use the wrong one, your code will crash!
• Spacing doesn’t matter
  • By convention people indent inside of a curly bracket block
    • Helps to keep track of which code is where
• All statements must be ended with a semicolon!
• All open curly brackets need a closing curly bracket
  • Same with quotes and parenthesis

1.2.1: My first Java program

• Every Java program is written as a “class”
  • Java is Object Oriented
    • Learn about that in Unit 2
  • Everything within a program is inside that class
• Can be a “main method”
  • Starts the program
  • This is what is executed when you ask Java to run a class

public class MyClass {
    public static void main(String[] args) {
        // Put your code here!
    }
}

A template for a simple Java program with a main method

1.2.2: Print commands

• Java has two different print commands
  • System.out.println(val)
    • Prints the value followed by a new line
  • System.out.print(val)
    • Prints the value; no new line
• System.out.println("Hi there!");
  • prints characters between first and last quote
  • "Hi there!" is a string literal
    • Can have any number of characters
• Most Java keywords are lowercase
  • Class names are uppercase
    • System or String
• Statements are terminated with a semicolon
  • Used like a period in english

1.2.3: Syntax Errors and Debugging

• We need to compile (translate) Java source code into class files which the computer can run
• Syntax errors are reported if your code isn’t properly written
  • A missing semicolon/curly bracket/quote could cause syntax errors
• Compiler errors will tell you the line number of the error and the type of error
  • Not always easy to understand
  • Sometimes the compiler is wrong about the line number!

How to debug

1. Describe your problem
   • What did you want your code to do, and what is it actually doing?
2. Hunt for bugs
   • What code is causing the bug?
3. Try out solutions
4. Document your learning

• Try explaining the bug out loud
  • Can be to a real person
  • Can be to no one
  • Can also be to a rubber duck!
    • (ducks are kind of fun)

My debugging ducks :)

1.2.4: Comments

• In Java, // is used to mark the beginning of a comment
• /* is used to begin a multi line comment
  • ended with */
• the compiler will skip over comments
  • They are still useful to document code and make notes about what something is doing
  • I make heavy use of // TODO to keep track of things I noticed but am not going to fix/improve right now

/*  MyClass.java
    Programmer: Nathan Jankowski
    Date: 10/2/2021
*/

public class MyClass {
  int max = 10;  // keeps track of max score
}

An example of commenting

1.2.5: Debugging Challenge

There isn’t much to note with this section, just debug the code to get an expected output.

1.2.6: Summary

public class MyClass {
  public static void main(String[] args) {
    System.out.println("Hi there!");
  }
}

A basic Java program

• A Java program starts with public class NameOfClass {}
  • Each class has it’s own file
    • Class name needs to match file name
    • NameOfClass.java
• the main method is invoked when a Java class is run
  • will always be public static void main(String[] args)
• System.out.println() and System.out.print() print to stdout
  • System.out.println also adds a line break to the end of the output
• A string literal is enclosed in double quotes
• Java statements are ended with a semicolon
• Curly brackets enclose blocks of code
• // and /* */ are used for comments
• A compiler translates source code into a class file which can be run.
  • If the source code is improperly written, the compiler will report the errors as syntax errors
  • Check for curly brackets, parenthesis, quotation marks, and semicolons

1.2.7: AP Practice

Nothing really to note here, just complete the activity.