question about a class

[kalar]

i want to ask a question about a class i found on a book
my problem is in projectedPopula tion method. I want to ask why we use the count and populationAmoun t variable .I mean where is the problem if i use years and population variables?
thanks !

public class Species {
	
	private String name;
	private int population;
	private double growthRate;
	
	public void readInput()
	{
              //  ................................
		System.out.println("What is the species's name?");
		name = keyboard.nextLine();
		
             //more code

			population = keyboard.nextInt();
		System.out.println("Enter growth rate (percent increase per year)");
		growthRate = keyboard.nextDouble();
		
	}
	
	public void writeOutput()
	{
		System.out.println("Name = " + name);
		System.out.println("Population = " + population);
		System.out.println("Growth rate = " + growthRate + "%");
	}

		

	
	public int projectedPopulation(int years)
	{
		double populationAmount = population;
		int count = years;
		while((count > 0) && (population > 0))
	    {
			populationAmount = (populationAmount + (growthRate/100)*populationAmount);
			count--;
		}
		
		if (populationAmount > 0)
			return (int)populationAmount;
		else
			return 0;
		
	};

[BigDaddyLH]

That method could have used years instead of introducing the local variable count. But there's a convention of treating method parameters as though they were constants. For example, you may want to amend the method with a print statement and use the original value of years in it. In any case, this is not a big issue.

On the other hand, not using field population in this method is crucial. This method shouldn't change the state of the Species object, right? So after calling it, the value of population should be the same. Therefore, don't touch it in this method.

[kalar]

Thank you @BigDaddyLH.
I am new to java so i make these questions.

So we don't use the years variable because maybe we need it . I mean this is not a java rule?
The second i understand it

[BigDaddyLH]

So we don't use the years variable because maybe we need it . I mean this is not a java rule?

It is a convention and not a rule of syntax. To verify this, edit the code and run it.

[kalar]

i run the code with years variable and it runs ok and the numbers are ok(should i got an error?)

but when i run the programm with population and not populationAmoun t the compile got an error

[BigDaddyLH]

i run the code with years variable and it runs ok and the numbers are ok(should i got an error?)

but when i run the programm with population and not populationAmoun t the compile got an error

I left my crystal ball at home so I don't know what compile-time error you got, but it was probably because population has type int and populationAmoun t has type double. This is easy to fix.

[kalar]

i got an error in line:
population = (population + (growthRate/100)*population );
with error:
possible loss of precision

[BigDaddyLH]

i got an error in line:
population = (population + (growthRate/100)*population );
with error:
possible loss of precision

Yes, that is because population should be a double.

[Ganon11]

I'm not so sure - you can't have a half a person, or a quarter a rabbit, so it makes sense to keep it as an int. When estimating size of populations, the decimal places might be included to increase accuracy of prediction (so you don't always round up or always round down). But I could see this temporary variable as an int instead of a double.

[BigDaddyLH]

I'm not so sure - you can't have a half a person, or a quarter a rabbit, so it makes sense to keep it as an int. When estimating size of populations, the decimal places might be included to increase accuracy of prediction (so you don't always round up or always round down). But I could see this temporary variable as an int instead of a double.

I had half a chicken for lunch ;-)

[Ganon11]

I bet you had half a dead chicken. And the other half was dead, too. Even if you had half a live chicken, I'm betting all parts of the chicken are now dead.

Besides, there's no boolean member of Species indicating the species deliciousness.

[BigDaddyLH]

I bet you had half a dead chicken. And the other half was dead, too. Even if you had half a live chicken, I'm betting all parts of the chicken are now dead.

Besides, there's no boolean member of Species indicating the species deliciousness.

All species are delicious if you cook 'em right. Except perhaps Bitter Melon.

[JosAH]

All species are delicious if you cook 'em right. Except perhaps Bitter Melon.

Bitter melons are ferocious little predators; they have fangs and claws. When
another creature like a cow (or Dan Quaille) accidentally trots around in a field
with bitter melons they react like piranhas: they rip the other animal to pieces
within a minute. Nasty little creatures they are, just like jalapenos ...

kind regards,

Jos ;-)