Adding the contents of a vector....

[Tekk]

If you have a vector and its members are 10,4,4,2 how would you make it so a method getSum() would add them.

[strangerstill]

Which language?

[Tekk]

hehe..silly me....its Java

[strangerstill]

hmm, thought it probably was, didn't want to end up with a totally unrelated answer

so, anyway, something like

public class MathVector extends Vector {
	double getSum() {
		if isEmpty()
			return 0;
		else {
			double sum = 0;
			for (int i = 0; i < size(); i++)
				sum += get(i);
			return sum;
		}
	}
}

?

[Tekk]

Cool Thanks....but now Im having problems figure out how to setup the constructor for my class. Here's what I have basically....

import java.io.*;
import java.util.*;
/////////////////////////////////////////////////
class Operator
{
private Vector v;
//----------------------------------------------
public Operator()
   {
   }
//----------------------------------------------
public static void testOperator()
   {
      v.addElement(new Integer(10));
      v.addElement(new Integer(4));
      v.addElement(new Integer(0));
      v.addElement(new Integer(4));
      v.addElement(new Integer(2));
      
      System.out.println("The min value is " + getMin());
      System.out.println("The max value is " + getMax());
      System.out.println("The sum is " + getSum());
      printPercentageOfSum();
      System.out.println("The sum of the square is " + getSumOfTheSquares());
      System.out.println("The standard deviation is " + getStandardDeviation());
   }
//----------------------------------------------
} // End of Operator
////////////////////////////////////////////////
class Hw03
{
//----------------------------------------------
public static void main(String[] args)
   {
      Operator.testOperator();
   }
//------------------------------------------------
} // End of Hw03

I only put in the testOperator method and constructor for the Operator class. What happens is that I am forced to put static in all the methods because testOperator is using non-static methods. I know its because of my constructor setup but I've fiddled and fiddled and can't figure out how I would set it up. Any ideas??? Try to point me in the right direction..hehe..thanks

[strangerstill]

Hmm...so getMin() etc. are methods on the Operator object? Well, those need to be non-static because they reference the Vector which has to be non-static...
so testOperator should be non-static as well because it calls non-static methods on its parent Operator object.
(I think - I'm not too good at java)
Does this make any sense?

[Tekk]

Well whats holding me up is that I need to figure out how to create a new Vector in the constructor. See...v has never really been created yet I call it in v.addElement(....) and that is why Im getting the null pointer exception error. I need to figure out the syntax for the constructor so that I can create v in the testOperator() method. But I can't figure out the syntax for it.

Im used just doing things like

Name a = new Name("firstName", "lastName");

That calls the constructor of the name class and creates a new name "a". But I need to do basically the same type of concept for this assignment but its the damn syntax I need. How can I create a new vector V using the constructor?

Also, the testOperator() method needs to be static because it is being called from the Hw03 class. Without the static it would not be present there.

[qball]

Try:

v = new Vector();

But that t'ain't gonna help you. Constructors are invoked when a class is instantiated, not when a class is loaded. A class is 'loaded' when a static class method is invoked.

In fact you cannot access your:

private Vector v;

in any static methods as v is an instance variable. The compiler should pick this up...

Without fully understanding class and instance vars and methods, keep everything static, thus:

static Vector v = new Vector();

[strangerstill]

aha, starting to understand.
in the constructor just put

v = new Vector(5);

that will create a Vector with an initial capacity of 5,

then keep everything as non-static, so you need to instantiate your Operator:

public static void main(String[] args)
   {
      Operator o = new Operator()
      o.testOperator();
   }

should have spotted that...

[strangerstill]

oh and to 'figure out the syntax for the constructor'.. there's one place to go for java reference and that's http://java.sun.com/j2se/1.4/docs/api/index.html