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Extending ArrayList of integer

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hell04

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Extending ArrayList of integer

Aug 28th, 2009

Hi all,
I have the following task;
Extend an ArrayList of Integer by adding a method called 'sum', that returns the total sum of the elements of the list of integers. Such that each time the method is called sum up all the integers.

So I started by making the following code but it is not working! Any Help Please.

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
import java.util.ArrayList;
 
public class Sum extends ArrayList<Integer> {
 
	ArrayList<Integer> num = new ArrayList<Integer>();
 
	num.add(1);
	num.add(13);
	num.add(24);
	num.add(65);
	num.add(67);
	num.add(89);
 
	return (num);
 
 
	public Integer Sum() {
 
		Double subtotal = 0.0;
		for (Double d : num) {
			subtotal += d;
 
		}
 
	}
 
}
import java.util.ArrayList;

public class Sum extends ArrayList<Integer> {

	ArrayList<Integer> num = new ArrayList<Integer>();

	num.add(1);
	num.add(13);
	num.add(24);
	num.add(65);
	num.add(67);
	num.add(89);

	return (num);

	
	public Integer Sum() {

		Double subtotal = 0.0;
		for (Double d : num) {
			subtotal += d;
			
		}

	}

}

Please Help

Last edited by ~s.o.s~; Aug 29th, 2009 at 10:57 am. Reason: Added code tags, please learn to use them.

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VernonDozier VernonDozier is offline

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Re: Extending ArrayList of integer

Aug 29th, 2009

•

Originally Posted by hell04

Hi all,
I have the following task;
Extend an ArrayList of Integer by adding a method called 'sum', that returns the total sum of the elements of the list of integers. Such that each time the method is called sum up all the integers.

So I started by making the following code but it is not working! Any Help Please.

import java.util.ArrayList;

public class Sum extends ArrayList<Integer> {

ArrayList<Integer> num = new ArrayList<Integer>();

num.add(1);
num.add(13);
num.add(24);
num.add(65);
num.add(67);
num.add(89);

return (num);

public Integer Sum() {

Double subtotal = 0.0;
for (Double d : num) {
subtotal += d;

}

}

}

Please Help

Code tags:

[code=JAVA]
// paste code here
[/code]

 Help with Code Tags 
 JAVA Syntax (Toggle Plain Text) 
import java.util.ArrayList;
 
public class Sum extends ArrayList<Integer> {
 
	ArrayList<Integer> num = new ArrayList<Integer>();
 
	num.add(1);
	num.add(13);
	num.add(24);
	num.add(65);
	num.add(67);
	num.add(89);
 
	return (num);
 
 
	public Integer Sum() {
 
		Double subtotal = 0.0;
		for (Double d : num) {
			subtotal += d;
 
		}
 
	}
 
}
import java.util.ArrayList;

public class Sum extends ArrayList<Integer> {

	ArrayList<Integer> num = new ArrayList<Integer>();

	num.add(1);
	num.add(13);
	num.add(24);
	num.add(65);
	num.add(67);
	num.add(89);

	return (num);

	
	public Integer Sum() {

		Double subtotal = 0.0;
		for (Double d : num) {
			subtotal += d;
			
		}

	}

}

Lines 5 through 14 just appear to be floating around. Are they part of a main function? Part of a constructor? Currently they're not part of anything.

Line 17 - The Sum function returns an Integer, but there's no "return" line, so you need to add one.

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hell04

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Re: Extending ArrayList of integer

Aug 29th, 2009

Actually I have no clue of how to fix line 4 to 17 but I have fixed the Sum method and it looks something like;

 Help with Code Tags 
 JAVA Syntax (Toggle Plain Text) 
public Integer Sum() {
 
		Integer subtotal = 0;
		for (Integer d : num) {
			subtotal += d;
			return subtotal;
		}
	}
public Integer Sum() {

		Integer subtotal = 0;
		for (Integer d : num) {
			subtotal += d;
			return subtotal;
		}
	}

But sum method is saying that it doesn't know what num is! Sorry I am new to this language and have no clue what I am doing

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Re: Extending ArrayList of integer

Aug 29th, 2009

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Actually I have no clue of how to fix line 4 to 17 but I have fixed the Sum method and it looks something like;

Well I can see how this can be fixed, but I need to know your motive in writing lines 4 to 17, are they for testing your code like in a main as VernonDozier says??
Also why does your sum() method need to return an "Integer" object, would an "int" not be just fine ?

Last edited by stephen84s; Aug 29th, 2009 at 11:22 am.

"Any fool can write code that a computer can understand. Good programmers write code that humans can understand."

"How to ask questions the smart way ?"

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Re: Extending ArrayList of integer

Aug 29th, 2009

•

Originally Posted by stephen84s

Well I can see how this can be fixed, but I need to know your motive in writing lines 4 to 17, are they for testing your code like in a main as VernonDozier says??
Also why does your sum() method need to return an "Integer" object, would an "int" not be just fine ?

It's gotta be the Driver/Tester/main function code. Make it obvious and take it all the way out of your class and put it in another class:

 Help with Code Tags 
 JAVA Syntax (Toggle Plain Text) 
public class Driver
{
    public static void main(String[] args)
    {
        MyArrayList num = new MyArrayList();
 
        num.add(1);
        num.add(13);
        num.add(24);
        num.add(65);
        num.add(67);
        num.add(89);
 
        int sum = num.Sum ();
        System.out.println (sum);
    }
}
public class Driver
{
    public static void main(String[] args)
    {
        MyArrayList num = new MyArrayList();

        num.add(1);
        num.add(13);
        num.add(24);
        num.add(65);
        num.add(67);
        num.add(89);

        int sum = num.Sum ();
        System.out.println (sum);
    }
}

Sum is not a good name for this class. It should be a method in the class. I renamed the class MyArrayList (and I switched from Integer to int, like Stephen mentioned. Switch it back if you like).

 Help with Code Tags 
 JAVA Syntax (Toggle Plain Text) 
import java.util.ArrayList;
 
public class MyArrayList extends ArrayList<Integer>
{
    public int Sum()
    {
        return 17;
    }
}
import java.util.ArrayList;

public class MyArrayList extends ArrayList<Integer>
{
    public int Sum()
    {
        return 17;
    }
}

It'll run as is, but obviously gives the wrong answer. Write the Sum function so it is correct. Don't use num unless you define it inside the Sum function. There is no connection between num in Driver's main function and what's in the Sum function.

You may want to use the keyword "this" in your function rather than num.

http://java.sun.com/docs/books/tutor...O/thiskey.html

Last edited by VernonDozier; Aug 29th, 2009 at 1:52 pm.

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hell04

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Re: Extending ArrayList of integer

Aug 30th, 2009

So VernonDozier should I in my Sum() method replace num with 'this'?

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Re: Extending ArrayList of integer

Aug 30th, 2009

•

Originally Posted by hell04

So VernonDozier should I in my Sum() method replace num with 'this'?

When in doubt, try it out. Does it compile? Does it run? Does it give good results?

Last edited by VernonDozier; Aug 30th, 2009 at 11:20 pm. Reason: Fixed grammar/spelling.

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hell04

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Re: Extending ArrayList of integer

Aug 31st, 2009

Ok after modifying I have the following code;

 Help with Code Tags 
 JAVA Syntax (Toggle Plain Text) 
import java.util.ArrayList;
 
public class MyArrayList extends ArrayList<Integer>{
 
	public Integer Sum(){		
 
		Integer sum1 = 0;
 
		for (Integer d : this) {
 
		sum1 += d;
		}
		return sum1;
	}
 
	public static void main (String args []){
 
}
}
 
and 
 
import java.util.ArrayList;
 
public class Driver{
 
 
 
	public  void main(String args[]){
 
		MyArrayList num = new MyArrayList();
 
		num.add(1);
		num.add(13);
		num.add(24);
		num.add(65);
		num.add(67);
		num.add(89);
		num.get(1);
		Integer sum = num.Sum();
 
		System.out.println(sum);
 
	}
 
}
import java.util.ArrayList;

public class MyArrayList extends ArrayList<Integer>{
	
	public Integer Sum(){		
		
		Integer sum1 = 0;
		
		for (Integer d : this) {
		
		sum1 += d;
		}
		return sum1;
	}

	public static void main (String args []){
	
}
}

and 

import java.util.ArrayList;

public class Driver{
	
	

	public  void main(String args[]){

		MyArrayList num = new MyArrayList();

		num.add(1);
		num.add(13);
		num.add(24);
		num.add(65);
		num.add(67);
		num.add(89);
		num.get(1);
		Integer sum = num.Sum();

		System.out.println(sum);
		
	}
	
}