The Java Programming Language

ID:276711
 
Feb 8 2006, 3:28 am
Well, recently I got my Java Compiler working after a long time of it not working and I started to learn Java.
The funny thing is, I never programmed in it before, and from only seeing a few examples of code from my friends notebook a few days beforehand, I was able to program basic classes that do basic things.

I can't find a good tutorial online that teaches everything in Java, such from what explain what everything does, arrays, io, etc.

I can do stuff, but I don't understand what some stuff actually means..
Example.

public class Main {
    public static void main(String args[])
    {
        System.out.println("Hello world.");
        int Money = 0;
        int Cost = 100;
        System.out.println(Cost-Money); 
        AlarmClock M = new AlarmClock();
        M.Snooze();
    }
}

I understand you must put "public static void main(String args[])" on most classes, but what do they mean? And using just "public void Test();" is much like creating a proc.

Help please?
Feb 8 2006, 3:56 am
main is the standard entry point for console application, and I guess Java Classes as well. Args[] is an associative array listing all of the arguments.

Also, with public void Test(); :

Public defines who can access it. In this case, anyone. If it's anything like C++'s access methods, then you can also have protected or private, which probably have a different definition in Java. Void is thge return type, in this case, nothing. Test is the function name, and everything in between the parenthesis is arguments, which are defined as

"Return-Type Var-Name".


Also, on Main, there's an extra word before the function name, "static"

Well, again if it's anything like C++, then it means that that function can be called without having an instance of the class that contains it.
Feb 8 2006, 5:06 am
I don't know Java, but that looks a lot like C++.... maybe I can pick up on Java then as well...

Java-folks, correct me here if I'm wrong, ok?

Anyhow, from my C++ perspective:

public class Main {


This is just the main class. In C++, the function "main" is called first, but I guess Java has to put the main function inside of a main class or something.

    public static void main(String args[])
    {


Here's the main function. Well, it's void in this case, so I guess it won't be returning any values. It's argument is a string array I guess?

        System.out.println("Hello world.");


Output "Hello world." to the console.

        int Money = 0;


Define a new integer called Money, set it equal to 0.

        int Cost = 100;



Define a new integer called Cost, set it equal to 100.

        System.out.println(Cost-Money);


Output the difference of the integer Cost's value, minus the integer Money's value.

        AlarmClock M = new AlarmClock();


Define a new AlarmClock called M, and instantiate it. This is a class object. That's like saying "int i = 0;" except it's an object defined in a class rather than an integer. I'm not sure if this is user-created or something Java has built-in.

        M.Snooze();


Call the method "Snooze" on the M (The AlarmClock we just defined) object.

    }
}


End curly brackets.

Guys, correct me if I'm wrong here, because I've never touched on Java. This looks a loooooot like the C++ I've done, though, so I assume some of it's similar.


~Kujila
Feb 8 2006, 5:11 am
In response to Kujila
Your mostly correct, before I got expelled this year I was taking java. What you have there looks pretty good for never touching java.
Feb 8 2006, 12:24 pm
I'm taking java now.

public class Main //<< -- Make this the name of the java file you save it in
{
    public /*Visible outside this file*/ static /*Instantiates vars only once*/ void /*Returns nothing*/ main(String args[]) // Main - executes on runtime, Args: arguments. 
    {
        System.out.println("Hello world."); // Print a line. println is like adding a '\n' to the end of the text. System.out.print(""); does not go to next line.
        int Money = 0; // define an integer called money.
        int Cost = 100; // define an integer called cost.
        System.out.println(Cost-Money);  // display the difference
        AlarmClock M = new AlarmClock(); // what does this class do?
        M.Snooze(); // Call a method of the class AlarmClock
    }
}


Java's a lot like C++, where I go to school C++ is a prerequisite to Java. Note this:
C++ -------- Java
function <--> method

Get it? I've got my "Fundamentals of Java" textbook with the yummy doughnuts on the front right here, if you need something else.


--Vito


--Vito
Feb 8 2006, 3:15 pm
In response to Vito Stolidus
You're nearly right, except that's not what "static" means. static means that the method (or variable, or whatever you happen to be declaring) belongs to the class itself, not objects of that class.

It's a subtle but clear-cut distinction. Here's an example:

public class SomeClass {
    public static void blahblah() {
        System.out.println("You called blahblah");
    }
    public void foobar() {
        System.out.println("You called foobar");
    }
}

/****
Assume that the below code is in another method somewhere.
*****/

SomeClass.blahblah(); // Works, blahblah is static
SomeClass.foobar(); // ERROR, foobar is not static

SomeClass instantiatedobject = new SomeClass();
instantiatedobject.blahblah(); // Works (static methods work even when called on objects)
instantiatedobject.foobar(); // Works


It's all to do with the difference between an object and its class. If you don't really understand this properly, don't worry too much at the moment. =)
Feb 8 2006, 5:34 pm
In response to Crispy
Static? Oh noes, reminds me of VB.NET! T_T

~Kujila
Feb 9 2006, 2:36 am
http://sepwww.stanford.edu/sep/josman/oop/oop1.htm - Don't Fear the Oop!
http://www.freewarejava.com/tutorials/index.shtml - Freewarejava tutorials
http://www.javacoffeebreak.com/tutorials/index.html - Java Coffee Break

my favorite: http://www.mindview.net/Books/TIJ/ Bruce Eckel's 'Thinking in Java' - very good book IMHO. I have a 2nd edition copy here (should get the 3rd edition someday) - free online / downloadable Java book.

Feb 26 2006, 4:16 pm
In response to Crispy
I don't know the context of this conversation, or if my input helps at all, but static as from C/C++ which is what Java was created off of means that that memory space will not be changed on the next call to the function. Variables are either static or dynamic (well they can be constant too and others but not worrying about that right now).

A function has it's own local variables lets say:

void add_1_and_2 ()
{
int x;



}
Feb 26 2006, 4:18 pm
In response to Peewee_RotA
disregard everything i just posted because a terrible design of DHTML form causes tab+space to post an incomplete message. The only web application I've seen more retarded than that is the whole of hotmail.com and all of its previous, current, and future versions
Feb 26 2006, 4:19 pm
In response to Peewee_RotA
Peewee_RotA wrote:
disregard everything i just posted because a terrible design of DHTML form causes tab+space to post an incomplete message. The only web application I've seen more retarded than that is the whole of hotmail.com and all of its previous, current, and future versions

First, you can edit your post. Second it's not a terrible design of DHTML form. It's a standard HTML form. Firefox/Internet Explorer are just doing what they're supposed to do. Tab makes you switch to the next focus-able item.
Feb 26 2006, 9:31 pm
In response to Jon88
Ive been learning java for some time now. Ive basically learned it all from this site (I cant believe noone put this down as its the most obvious) http://java.sun.com/docs/books/tutorial/index.html
This will teach you everything you will want to know about java.

ADT_CLONE
Feb 26 2006, 10:54 pm
From the syllabus, it looks like the Computer Science component of the Software Engineering course I'm doing at uni is mostly composed of Java.

I've had a few glances through the textbook we're using (Big Java, by Horstmann, if you're interested), and I have a one word description of Java so far:

Ugh.

That syntax is ugly. And any language that often runs into constructs like 'public static double height = 1342.67' is just annoying.

And the GUI is just crufty beyond measure.
Feb 27 2006, 12:58 am
In response to Jp
Welcome to my world. =P

Luckily I think I'll be able to skip most of the Java in my course, but yeah... ick. Very ick.