Java 102 - Understanding Java Syntax: Classes, Methods, main() Method, and Print Statements

📌 Introduction

After setting up Java and running your first program, it’s time to understand Java’s core syntax. In this blog, we will cover essential Java elements: Classes, Methods, the main() Method, and Print Statements. Mastering these concepts will help you write efficient Java programs.

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📌 1. Java Classes – The Building Blocks

🔹 What is a Class?

A class in Java is a blueprint for objects. It defines properties (variables) and behaviors (methods). Every Java program must have at least one class.

🔹 Creating a Class

Here’s a simple example of a Java class:

// Defining a class
public class MyClass {
    // Fields (Variables)
    int x = 10;
}

🔹 Instantiating a Class (Creating an Object)

To use a class, we need to create an object:

public class Main {
    public static void main(String[] args) {
        MyClass obj = new MyClass(); // Creating an object
        System.out.println(obj.x); // Accessing the variable
    }
}

✅ Output: 10

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📌 2. Methods in Java

🔹 What is a Method?

A method is a block of code that performs a specific task. Methods make programs modular and reusable.

🔹 Defining a Method

public class MyClass {
    // Method definition
    public void sayHello() {
        System.out.println("Hello, Java!");
    }
}

🔹 Calling a Method

public class Main {
    public static void main(String[] args) {
        MyClass obj = new MyClass();
        obj.sayHello(); // Calling the method
    }
}

✅ Output: Hello, Java!

🔹 Method with Parameters

public class MyClass {
    public void greet(String name) {
        System.out.println("Hello, " + name + "!");
    }
}

🔹 Calling the Method

public class Main {
    public static void main(String[] args) {
        MyClass obj = new MyClass();
        obj.greet("Alice");
    }
}

✅ Output: Hello, Alice!

🔹 Method with Return Type

public class Calculator {
    public int add(int a, int b) {
        return a + b;
    }
}

public class Main {
    public static void main(String[] args) {
        Calculator calc = new Calculator();
        int result = calc.add(5, 7);
        System.out.println("Sum: " + result);
    }
}

✅ Output: Sum: 12

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📌 3. The main() Method – Java’s Entry Point

🔹 What is main()?

Every Java program starts execution from the main() method. It serves as the entry point.

public class Main {
    public static void main(String[] args) {
        System.out.println("Java Program Started");
    }
}

✅ Output: Java Program Started

🔹 Understanding the main() Method

public static void main(String[] args) {

• public → Accessible from anywhere.

• static → No need to create an object to call it.

• void → No return value.

• main → Method name.

• String[] args → Used for command-line arguments.

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📌 4. Print Statements in Java

🔹 Printing Output

Java provides System.out.println() to print messages:

System.out.println("Hello, Java!");

✅ Output: Hello, Java!

🔹 Print vs. Println

System.out.print("Hello, ");
System.out.print("Java!");

✅ Output: Hello, Java! (on the same line)

System.out.println("Hello, ");
System.out.println("Java!");

✅ Output:

Hello,
Java!

🔹 Formatting Output

int age = 20;
System.out.printf("I am %d years old.", age);

✅ Output: I am 20 years old.

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📌 5. Common Errors & Fixes

❌ Forgetting to Define the main() Method

❌ Error: Main method not found ✅ Fix: Ensure your class has public static void main(String[] args)

❌ Forgetting Semicolons

❌ Error: ';' expected ✅ Fix: End each statement with ;

❌ Mismatched Brackets

❌ Error: '}' expected ✅ Fix: Ensure each { has a corresponding }

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📌 6. Next Steps

🎯 Now that you understand Java syntax, here’s what to learn next: ✅ Java Variables & Data Types ✅ Operators & Control Statements ✅ Loops & Arrays

Stay tuned for our next blog: “Mastering Java Variables & Data Types” 🚀

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📌 Summary

✔ Java programs are written inside classes. ✔ Methods define reusable code blocks. ✔ The main() method is the entry point. ✔ System.out.println() is used for printing output.

With this knowledge, you’re ready to start writing Java programs! 💻🔥