Creating Your First Java Application, Hello World! Java

Tags:

Java

Create Your First Application Program

public class HelloWorld { // class start

    public static void main(String[] args) { // method start
        System.out.println("Hello World! Java.");
    }
}

Notes When Writing Source Code

English uppercase and lowercase letters are distinguished.
When saving, the file name must match the class name, and the extension is .java.
HelloWorld.java
Compile
```
javac HelloWorld.java
```
Run
```
java HelloWorld
```

Class Definition

Because Java programs are written in units of classes, a class must be defined in the source file.
By convention, a class name starts with an uppercase letter.
Class components(properties, methods, and so on) are placed inside { }.
When saving a source file, the file name must match the class name. This excludes cases where multiple classes exist in one file.

Defining the `main(String[] args)` Method

At least one must exist for an application program to run.
It is the entry point of the program, is called first by the JVM, and sequentially executes the statements written inside the main method block.
The JVM recognizes a statement ending with a semicolon(;) as one command statement.
Comments are used to make program source code easier to understand and do not affect compilation or execution.