Java Syntax
Java Syntax
In the previous chapter, we created a Java file called Main.java
, and we used the following code to print "Hello World" to the screen:
Main.java
public class Main {
public static void main(String[] args) {
System.out.println("Hello World");
}
}
Example explained
Every line of code that runs in Java must be inside a class
.
And the class name should always start with
an uppercase first letter. In our example, we named the class Main.
Note: Java is case-sensitive: "MyClass" and "myclass" has different meaning.
The name of the java file must match the class name. When saving the file, save it using the class name and add ".java" to the end of the filename. To run the example above on your computer, make sure that Java is properly installed: Go to the Get Started Chapter for how to install Java. The output should be:
Hello World
The main Method
The main()
method is required and you will
see it in every Java
program:
public static void main(String[] args)
Any code inside the main()
method will be executed.
Don't worry about the keywords before and after it. You will get to know
them bit by bit while reading this tutorial.
For now, just remember that every Java program has a class
name which
must match the filename, and that every program must contain the
main()
method.
System.out.println()
Inside the main()
method, we can use the println()
method to print a line of text to the screen:
public static void main(String[] args) {
System.out.println("Hello World");
}
Note: The curly braces {}
marks the beginning and the end of a block of code.
System
is a built-in Java class that contains useful members, such as out
,
which is short for "output". The println()
method, short for
"print line", is used to print a value to the screen (or a file).
Don't worry too much about how System
, out
and println()
works. Just know that you need them
together to print stuff to the screen.
You should also note that each code statement must end with a semicolon (;
).