I.e., filmQuiz, filmquiz, and Filmquiz would all be different classes.
Our first Class
Starting with a blank file, we add the following code...
public class HelloWorld {
}
And save it as HelloWorld.java
Won't do anything - needs something between its brackets {}.
public and class are keywords: words you can only use in special contexts.
The public bit isn't always needed here, but helps.
Blocks
The area between the brackets is known as a block.
These are used to divide up Java code into areas that do different things.
These can be nested inside each other.
They usually start with a "declaration" of what they are (e.g. the class declaration "public class HelloWorld").
public class HelloWorld {
{
Code to do stuff would go here.
}
}
The first thing we need is a 'main' block.
The starting class
When you pass a file to the interpreter, the interpreter looks in the class for a block called main. It knows all the instructions for how to start are in this block.
Without a main block the interpreter wouldn't know where to start - so you must have one to start the interpreter.
Only one class in a full program need have one.
Main block
public class HelloWorld {
public static void main (String args[]){
}
}
Don't worry about the details ('static' etc.) we'll cover these at a later point.
Any class with a main block can be 'run'.
That's the tricky bit done
We've made our starting class, and told the interpreter where to start.
Now we just have to fill the main block with stuff to do.
This is where we really start the coding.
Cheesy example
public class HelloWorld {
public static void main (String args[]){
System.out.println("Hello World");
}
}
'Prints' (writes) "Hello World" to the screen (the command line).
Note that it uses a class called 'System' to print.
Note that all lines not followed by a block end in a semi-colon ("statements").
Review
We define classes which have code in them to do stuff.
Blocks are section of code that do stuff. Lines that don't end in blocks end in semi-colons.
The first class you pass to the interpreter must have a 'main' block, with instructions of what to do to first run the program.