Introduction to Java

Instructor: Chris Fulton

Learning Objectives

• Explain the necessary components needed to download, run and execute a Java program
• Context - Java | Java API | Java Virtual Machine (JVM)
• What is needed - Editors, Compilers, and Interpreters
• Interpret a basic Java program
• Project structure | import | Main() | Method Declaration | Method Body | Statements
• Explore the declaration and use of variables
• Java primitive data types
• Variable declaration and initialization | Parsing and Casting
• Execute, compile and debug a basic program
• Types of Errors: Compile-time | Run-time | Logical
• Debugging and Commenting Code
• Utilizing Java API - Java System Class
• Creating Interactive programs using Scanner Class| Escape Sequences | Formatting
• Utilizing source control to keep track of changes, track history and experiment with code
• Downloading starter code and uploading Programs using Git
• Overview of Version Control using Git

Context

What is needed to run Java?

The JDK (Java Development Kit)

Contains two major parts

• The Java Runtime Environment (JRE) includes:
• Java Virtual Machine (JVM)
• Java API or Java Standard Class Library
• Java Development Tools
• Java Compiler aka javac
• Java documentation aka javadoc
• Java Archive Resource files aka jar
• etc...

JDK Overview

The JVM primary job

Sample Program Break-down

Program Components

Declaring & Initializing Variables

Terms

Data Types

What does it mean by signed and unsigned? What's the difference between bit and bytes?

Learning Activity - number guess boxes

Unicode - ASCII - Binary

Reserved var keyword

							
								
	class Program
    {
        static void aMethod()
        {
			//Using primitive data type
			double monthlySalary = 9200.00;
			
			//Using Var keyword
			var yearlySalary = monthlySalary *12;
	  
			System.out.println(yearlySalary);
		}
    }
							
						

Java lets you declare local variables without giving them explicit types. The data type is implied at runtime.

Compiling, Debugging and Executing a program

Possible Errors in Execute, Compile and Debug a Java Progam

When compiling and running a program, any of the three errors can occur.

Steps to compile via command line

Syntax Error

								
									
									public class Movie{

										public static void main(String[] args) {
										
										   string marvelMovie = "The Avengers Infinity War"

										   System.out.printLine(marvelMovie + " is the best Marvel Movie"); 
									}
							
								
							

								
									
									public class Movie{

										public static void main(String[] args) {

										   String marvelMovie = "The Avengers Infinity War";

										   System.out.println(marvelMovie + " is the best Marvel Movie"); 
										}
									}

								
							

Logical Error

								
									
									public class Discount{

										public static void main(String[] args) {

										   double price = 23.00;

										   double discount = .10;

										   price = discount *(price - 1);

										   System.out.println("With discount the price is " +  price); 
										}
									}
							
								
							

								
									
									public class Discount{

										public static void main(String[] args) {

										   double price = 23.00;

										   double discount = .10;
										   
										   price = (1 - discount) * price;

										   System.out.println("With discount the price is " +  price); 
										}
									}

								
							

Run-time Errors

								
									
									public class Calculations{

										public static void main(String[] args) {

										   int number1 = 32, number2 = 0, result = 0;

										   result = number1/number2;

										   System.out.println("The result is" +result);

										}
									}
							
								
							

								
									
									public class Calculations{

										public static void main(String[] args) {


										   int number1 = 32, number2 = 0, result = 0;

										   try{

										       result = number1/number2;

											   System.out.println("The result is" +result);
										   }

										   catch(ArithmeticException e) {

											System.out.println ("Can't be divided by Zero " + e);

										   }
										  
										}

									}

								
							

Debugging in Visual Studio Code

• Debugging
• The process of removing all syntax and logical errors from the program
• Syntax errorsare discovered through compilation. Logical errors are discovered through testing
• Commenting out portions of your code is another way to help debug and narrow the issue.
• 1) Set a breakpoint. 2) Open Debug window - play button that has bug on it. 3) Step through code and observe variable assignment and call stack.

System and Scanner Class

Scanner Class

To implement the Scanner class, you must import import java.util.*;package

The Scanner class allows for input operations - reading input from the console

Analyzing Program w/Scanner Class

							
								import java.util.Scanner;
								
								public class Program{
									public static void main(String[] args){

										//Declarations
										String name, program;
										int creditHours;
										double tuitionCost;
										final double TUITION = 780.00;
										
										Scanner scn = new Scanner(System.in);  // Create a Scanner object
										
										System.out.println("Please enter your name: ");
										name = scn.nextLine();
										
										System.out.println("Please enter program: ");
										program = scn.nextLine();
										
										System.out.println("Please enter number of credits for this semester: ");
										creditHours = scn.nextInt();
										
										tuitionCost = TUITION * creditHours;
											
										System.out.println(name + " Thank you for entering your information. \n" + 
															"Your tuition for the semester is: " + tuitionCost);
									}
								}


							
						

System Class

The System package is imported by default, no need for an import statement

The System class offers access to input/output operations, but can also provide access to system level information.

Analyzing Program w/System Class

							
								import java.util.Scanner;
								
								class Program{
									static void Main(String[] args){

										long startTime = System.nanoTime(); //Gets the time before evaluating next statements
	 
										System.out.println("Your System properties");
										System.out.println("**********************");
										Properties p = System.getProperties();  //Creating a new instance of 
										System.out.println("User name: " + p.getProperty("user.name")); //get User's account name  
										System.out.println("User home directory: " + p.getProperty("user.home")); //get User's home directory  
										System.out.println("User current working directory: " + p.getProperty("user.dir")); //get User's current working directory  
										System.out.println("User Operating System: " + p.getProperty("os.name")); //get operating System
										System.out.println("User Operating System version: " + p.getProperty("os.version")); //get operating system version
										
										long elapsedTime = System.nanoTime() - startTime; //Calculate after executing getProperty() statements
										
												// 1 second = 1_000_000_000 nano seconds
										double elapsedTimeInSecond = (double) elapsedTime / 1_000_000_000;
								
										System.out.println("Time in seconds it took to execute program: " + elapsedTimeInSecond + " seconds");
									}
								}


							
						

Escape Sequence

Formatting Floating-Point Values

Utilizing Source Control

Version Control + Git

Source: https://scriptcrunch.com/295/

Version Control

The task of keeping a software system consisting of many versions and configurations well organized.

What is Git?

Git is a free and open source distributed version control system designed to handle everything from small to very large projects with speed and efficiency.

Download and install Git

• Navigate to git-scm.com
• Download the latest release for your operating system
• Install using default configurations - For windows a git bash terminal will come with your download. For macs you will use terminal for your git.
• Once downloaded, open the "Git bash" terminal and enter the command git --version

Commonly Used Git commands - Cheatsheet

The cheatsheet represents some of the most used commands that allow you to achieve the Git workflow.

Click here for an exhaustive book on git commands

Git workflow

Going through this workflow allows us to keep track of the changes we are making.

Git Command Practice

						
							public class App{
								public static void main(String[] args) {
							
								   double price = 23.00;
								   double discount = .10;
								   price = (1 - discount) * price;
								   System.out.println("With discount the price is " +  price); 
								}
							}
						
					

For this activity, we'll keep track of the changes we make to a simple java program

Git Branching & Merging

Branching allows you to create a copy of your main branch. You can experiment and test new functionality on new branches. Branching allows you to keep your main branch clean.