/my-first-java-app

An introduction to Java.

Primary LanguageJava

My-First-Java-App

This repo hosts various exercises to learn Java, the same exercises can be found at Codecademy. The purpose of this repo is to practice Java utilizing an IDE (Integrated Development Environment), namely VS Code.

Contents

Install Java

Create a Java Project

Mac:

  • Inside of Visual Studio Code, hold command + shift + p type Java: Create Java Project... and hit return

Windows:

  • Inside of Visual Studio Code, hold ctrl + shift + p type Java: Create Java Project... and hit enter

A prompt will appear, select No build tools for now.

Select a desired location for your Java Project (Note: A directory will be created at the desired location)

Finally, you will be prompted to name your Java Project

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Cloning this Repo

To clone this repo, cd into your desired directory and simply run the command:

git clone https://github.com/csalguera/my-first-java-app

To make a blank slate for practice of these exercises, run the following commands:

cd my-first-java-app
rm -rf ./src
mkdir ./src ./.vscode ./lib
touch ./.vscode/settings.json

Open your local repository in VS Code by running the following command:

open -a "Visual Studio Code" .

Inside of your .vscode directory, locate the settings.json file and paste the following:

{
  "java.project.sourcePaths": ["src"],
  "java.project.outputPath": "bin",
  "java.project.referencedLibraries": [
    "lib/**/*.jar"
  ]
}

Finally, if you would like to have your own Remote Repo, run the following commands:

rm -rf .git
git init
git remote add origin <YourRemoteRepository>

Make your first commit with the following commands:

git add .
git commit -m "initial commit"
git push -u origin main
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HelloYou

Inside your src directory touch a HelloYou.java file, that contains a HelloYou class with a main() method.

Inside main(), add a statement which prints Hello someName!, with your name replacing someName. Make sure to end the statement with a semicolon.

For example, if your name were “Maria,” the program would print Hello Maria!.

public class HelloYou {
  public static void main(String[] args) {
    System.out.println();
  }
}
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HideAndSeek

Inside your src directory touch a HideAndSekk.java file.

Inside main() and underneath the print statement System.out.println("Let's play hide and seek.");, output the following two statements using System.out.print():

"Three..."

"Two..."

Underneath your previous statements, output the following two text values using System.out.println():

"One..."

"Ready or not, here I come!"

public class HideAndSeek {
  public static void main(String[] args) {
    System.out.println("Let's play hide and seek.");
  }
}
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Timeline

Inside your src directory touch a Timeline.java file with plain text information about Java.

Plain text facts aren’t valid syntax. We’ll use comments to avoid breaking the program.

Use the single-line comment syntax for the first fact.

Change this line into a comment:

Sun Microsystems announced the release of Java in 1995

public class Timeline {
  public static void main(String[] args) {
    System.out.println("Hello Java!");

    System.out.println("You were born in 1995");

    Sun Microsystems announced the release of Java in 1995

    System.out.println("You were created by James Gosling");

    James Gosling is a Canadian engineer who 
    created Java while working at Sun Microsystems.
    His favorite number is the square root of 2!

    System.out.println("You are a fun language!");
  }
}

Our program is still broken!

Use the multi-line syntax to make these lines into a single comment:

James Gosling is a Canadian engineer who

created Java while working at Sun Microsystems.

His favorite number is the square root of 2!

You should still see You are a fun language! printed!

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LanguageFacts

Inside your src directory touch a LanguageFacts.java file that prints information about Java to the screen.

Unfortunately, the file does not have whitespace.

Make the file easier to read by adding a newline after each statement!

Press enter or return after each semicolon!

public class LanguageFacts {
  public static void main(String[] args) {
    System.out.println("Java is a class-based language.");System.out.println("Java classes have a 'main' method.");System.out.println("Java statements end with a semicolon.");
  }
}

Inside main(), add a new statement printing how you feel about coding.

Start the message with: “Programming is… “.

Remember to place a semicolon at the end of the statement!

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Compiling

Let’s practice compiling and executing a file by entering commands in the terminal!

Our text editor contains a broken program so we can see how compilers help us catch mistakes. Don’t make any corrections!

Inside your src directory touch a Compiling.java file.

In the terminal, type this command: javac Compiling.java and press enter or return.

public class Compiling {
  public static void main(String[] args) {
    System.out.println("Java is a class-based language.");
    System.out.println("Java classes have a 'main' method.");
    System.out.println("Java statements end with a semicolon.")
    System.out.println("Programming is... fun!");
  }
}

Do you see the error?

The compiler is telling us one of the print statements is missing a semicolon.

Change into your src directory by running the command: cd ./src

In the terminal, type ls and press return or enter.

ls is short for "list" and this command lists all the available files.

There should be a Compiling.java file, we did not successfully compile the file because of the error.

Add the missing semicolon in the text editor.

Let’s compile and execute our program!

Run the ls command in the terminal to see the uncompiled .java file.

Compile the file from the terminal.

Enter ls again to see the new .class file.

Run the executable file from the terminal by running this command: java Compiling

After executing your file, delete it by running the command: rm -rf Compiling.class and change back to the parent directory by running the command: cd ..

(Note: Java files are automatically compiled from your src directory into your bin directory. Alternatively, you can change into your bin directory with the command: cd ./bin and run the executable file from the terminal by running this command: java Compiling. To change back into your parent directory run the command: cd ..)

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Review

Inside of your src directory touch a Review.java file and fill it in!

Define a public class named Review.

Use opening and closing curly braces for the scope of the class.

Remember, no semicolons for classes or methods!

This code produces an error because Java programs need a main() method.

Define the main() method within the curly braces of the Review class.

Inside of the curly braces for the main() method, write The main method executes the tasks of the class as a single-line comment.

Below the comment, write a statement that prints the following: My first Java program from scratch!.

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