Java Explained: A Comprehensive Guide for Beginners |

If you're struggling with Java, don't worry. Take a nice deep breath, sit back, and let this article show you everything you need to know. This guide is made so you can read it on your phone or follow along with the code examples if you want.

With over 8+ years of programming experience in Java and a Computer Science degree, I understand the common hurdles learners face. I had my own breakdown in college when I thought I couldn't get through the projects, so I know it can be really hard. My goal is to help you out, wherever you are in your life with programming, and hopefully, you find this article helpful. This is everything you need to know about Java in a short read.

Understanding the Basics

Computers only understand zeros and ones, which makes it difficult for humans to communicate with them directly. To solve this, we made programming languages, which are just a bunch of keywords and symbols that help us program a computer. The one we're learning today is obviously Java, and here's everything you need to know to get started.

Setting Up Your Environment

To begin, you need a programming environment. This is where you write and run code. You can write code in Notepad or on a piece of paper, but neither of those has a way to compile your code, which means turning it into the zeros and ones a computer understands.

There are numerous tutorials on how to install an Integrated Development Environment (IDE). Eclipse and IntelliJ are both excellent choices.

Once your IDE is set up, you can create a file to start learning Java. 1. Go to File > New > Java Project. 2. Give the project a name, like Java-For-Real-Epicness, and hit Finish. 3. Expand the project folder, right-click on the src (source) folder, and select New > Class. 4. Name your Java file, for example, LearnJava. 5. Check the box for public static void main(String[] args). 6. Hit Finish.

You will see some code pop up on the screen. As mentioned, a programming language is just a bunch of keywords and symbols, and this Java file already has some for us.

public class LearnJava {
    public static void main(String[] args) {
        // Your code goes here
    }
}

Storing Data in Java

A super useful thing we can do in Java is store data. For instance, you can store a number in a variable like this:

int a = 5;

This takes the value 5 and stores it in a variable named a. The keyword int stands for integer. There are several other similar types.

Here are a few more: * char: Stands for character. char b = 'c'; * long: For very large integer numbers. * double: For decimal numbers.

These are called primitive types. The word primitive just means it was here before—it's built directly into Java.

Non-Primitive Types: The Power of Objects

Storing data is incredibly useful. If we wanted to change a username on an application like Instagram, it has to be stored somehow. To store a bunch of characters, like a name, you would use a String.

String name = "Susan";

Most statements in Java end in a semicolon. These symbols help Java parse the code, which just means going through it to make sense of it all.

Notice how String is capitalized and doesn't turn purple in many IDEs? It's not a primitive type; it's an object. You can do so many things with objects.

To see what you can do, just type the name of the variable followed by a period (.). The period is one of the most important symbols in Java because it reveals everything that the variable can do for you. Your IDE will most likely show a box with a list of available actions.

For example, we can convert our string to uppercase.

name.toUpperCase();

But how do we see this working? There's a great piece of code to print things to the screen so you can see them.

System.out.println(name.toUpperCase());

If you save and run this code, you will see "SUSAN" printed in your console window. You can try another action, like toLowerCase().

System.out.println(name.toLowerCase()); // Prints "susan"

Methods: The Building Blocks of Action

The toUpperCase() and println() functions have parentheses. Anything with parentheses like this is almost always a method. Methods are amazing because they just do things for you.

Let's make a method that adds an exclamation mark to the end of any string you want.

public static void addExclamationPoint(String s) {
    System.out.println(s + "!");
}

public static void are just keywords for now; each has its own purpose.
addExclamationPoint is our method name.
(String s) means it takes a String as input.
The code inside the curly braces {} is what runs.

To combine two strings, you use a plus sign (+). Now, to run this method, we have to call it.

// In the main method
addExclamationPoint("hotdogs"); // Prints "hotdogs!"

You can also return the result as a variable instead of printing it directly.

public static String addExclamationPoint(String s) {
    return s + "!";
}

Notice the keyword void was changed to String. This tells Java that the method will return a String value. Now we can store the result.

// In the main method
String exclaim = addExclamationPoint("hotdogs");
System.out.println(exclaim); // Also prints "hotdogs!"

Working Across Multiple Files with Classes

You can call methods that are in the same Java file directly. But what if you want to use code from another Java file?

Right-click the src folder again and create a new class called Animal.
In the Animal.java file, create a simple method.

public class Animal {
    public String iAmDog() {
        return "I am a dog";
    }
}

Now, back in your LearnJava.java file, you can use the iAmDog method. To do this, you first need to create an Animal object.

// In the main method
Animal a = new Animal();

Anytime you're making an object, it will generally follow this format: ClassName variableName = new ClassName();.

Now, you can use the dot operator on your new object to see what it can do.

String dog = a.iAmDog();
System.out.println(dog); // Prints "I am a dog"

A class is just a Java file that helps us make objects. Examples of commonly used objects are ArrayList and HashMap. However, many objects are not available by default; you have to import them.

For example, to use an ArrayList: ```java import java.util.ArrayList; // This line brings in the ArrayList code

public class LearnJava { public static void main(String[] args) { ArrayList list = new ArrayList<>(); list.add("item1"); } } ``AnArrayListallows you to do things likeadd,remove, andreplace` items in a list. It's how you might store a list of movies or users.

Objects and methods are super powerful. Each object has its own methods. This is why Java is referred to as OOP (Object-Oriented Programming). Each class represents an object, which has its own methods.

Essential Programming Logic

So, how do you make a method that does something cool? You use logic.

If-Else Statements

You can execute code based on a condition using an if statement.

int a = 5;

if (a == 0) { // Note: two equal signs for comparison
    System.out.println("a is zero");
} else if (a == 1) {
    System.out.println("a is one");
} else {
    System.out.println("a is something else");
}

For Loops

You can repeat code using a for loop. The following format will repeat the code inside it 5 times.

for (int i = 0; i < 5; i++) {
    System.out.println("Repeating...");
}

You can even put a for loop inside another for loop. If each loop runs 8 times, the inner code will run 64 times (8 * 8).

While Loops

You can repeat code until a certain condition is met using a while loop.

int a = 5;
while (a < 10) {
    System.out.println("hi");
    a++; // This adds 1 to a each time to prevent an infinite loop
}

Try-Catch Blocks

To handle errors gracefully, you can use a try-catch block. It will try to run the code inside the first block. If something goes wrong, an exception is thrown, and the code inside the catch block will run.

try {
    // Code that might fail
} catch (Exception e) {
    // Code to run if an error occurs
    System.out.println("Something went wrong!");
}

Using External Code with APIs

You can use other people's code and methods inside your own through an API (Application Programming Interface). An API is pretty much just a long list of methods you can use that were made by someone else, like Google, YouTube, Instagram, or Twitter.

To use someone else's API, you generally follow these steps: 1. Go to their website and download a .jar file. 2. In your project, right-click and go to Properties > Java Build Path. 3. Click Add External JARs and select the file you downloaded. 4. Use an import statement for the code you want to use. 5. You can now use the code they wrote in your program.

Conclusion

That's a high-level overview of everything you need to know to get started with Java. We went over primitive types, variables, storing data, objects, classes, methods, and core logic like if-else statements and loops. I really hope this helped you get started on your journey.