Thread: Help im a java noob!

Originally Posted by jonathanfox

should return the second list as well [b]ut [I']m not sure how to ...

Here's the thing: In Java a function can return (at most) one thing.

If you want the function to "return" two things and the things are reference objects, you can send the function some "containers" and let the function fill them up

First of all: Before writing code for the function, think (yes think) about how you are going to write a function that calls the Split() function. Think (really: think) about how you are going to test the program.

I mean, you are going to do this (eventually) anyhow. I respectfully suggest that program design start at the top (the main() function of your program) and work your way down.

There are many other ways to implement the functionality, but I'll start with the kind of Split function that I think you have in mind.

import java.util.ArrayList;
 
public class z // Or whatever name you want for your program.  I really
               // wanted "Z" but that's reserved for Zorro.
               // So...I will break with convention and use lower case "z"
{
    public static void main(String [] args)
    {
        // Will (probably) eventually read the list from
        // a file (or, maybe, from user command line or
        // some such thing).
        // For now, just initialize it with hard-coding.
        ArrayList<Integer> numbers = new ArrayList<Integer>();
        numbers.add(1);
        numbers.add(5);
        numbers.add(21);
        numbers.add(43);
        numbers.add(60);
        numbers.add(70);
        numbers.add(80);
        numbers.add(90);
        numbers.add(100);
        ArrayList<Integer> first  = new ArrayList<Integer>();
        ArrayList<Integer> second = new ArrayList<Integer>();
        int n = 70;
 
        Split(numbers, n, first, second);
 
        System.out.println("Original: " + numbers);
        System.out.println("First   : " + first);
        System.out.println("Second  : " + second);        
    } // End of main function
 
    static void Split(ArrayList<Integer>a, int n, ArrayList<Integer> b, ArrayList<Integer> c)
    {
        b.clear(); // Make sure it's empty to start with.
        c.clear(); // Ditto
        //
        // Fill up the arrays b and c with items from array a as directed by the Program Specification.
        //
    } // End of Split function
} // End of class definition

Output could look like this:

Original: [1, 5, 21, 43, 60, 70, 80, 90, 100]
First   : [1, 5, 21, 43, 60]
Second  : [70, 80, 90, 100]

Originally Posted by jonathanfox

there [are] a lot of small things in java [I] have to learn

There are no "small things" in Java. Every blasted, bloomin' thing is a Big Thing. The Good News: You don' t have to learn them all at once.


Cheers!

Z

Originally Posted by jonathanfox

. is a function the same as a method?

The word "function" is generic and is used in lots of other programming languages, not just Java. In most general terms: A function is something that can take some arguments and can return a value. It may or may not do something useful in the meanwhile.

A method in Java (and other languages with object-oriented constructs) is a term used for a function that is associated with a class. An object or instance method is associated with a particular object and inherently has an invisible parameter (called "this") that allows it to access data members and other methods of that object without having an explicit parameter for that object.

There are also static methods for classes. A static method is not associated with a particular object (so it doesn't have the implicit "this" parameter). The java Math library class has static methods sin(), cos(), pow(), etc...

Some other languages (C and C++ for example) have pointer data types, and it's possible in those languages to have a pointer variable whose value is the virtual runtime address of a function. That allows any part of the program to invoke a function by dereferencing that pointer. You can pass a function pointer to a function or method and a function or method can return a function pointer.

Remember we are not talking about Java here. Java doesn't have pointers that user programs can work with.

I wasn't there when Java was created, but in my mind I can almost hear the Java creators agree on something like: "Man, there are a ton of bad C programs out there that misuse pointers. So the first rule, and the most important, absolutely immutable precept of Java is: No Pointers!" (Or some such thing.) When I finish my Wayback Machine, I am going to confirm my suspicion. It was only about 20 years ago, and that's just about right for the initial shakedown cruise of the W.M.

Now, graphics programs in C and C++ use function pointers, among other things, to make it easy to implement "callback" functions, and some kind of "callback" mechanism is usually considered to be required for any decently structured program dealing with, say, mouse clicks. In Java, it is possible to get the (almost) equivalent functionality by using a Java mechanism called an "interface." That's how Java graphics library functions (typically) do it. Do you really want to get into that at your present state of development? (A rhetorical question. I don't expect an answer. I don't need an answer. I don't want an answer.)

Originally Posted by jonathanfox

...do i sound really stupid

No, you don't sound really stupid. The ones that sound really stupid are people who sprinkle "lol" throughout their communications.

Originally Posted by jonathanfox

haha

Well, a little hokey, but still not as trite as lol. Actually, I like a little "haha" from time to time but I usually reserve "lol" for tête-à-tête.


About stupidity in general, I wish I had said it first:

""Men are born ignorant, not stupid;
they are made stupid by education."
---Bertrand Russell


Good old Bertie. What a hoot!

Cheers!

Z