how to point a local variable of another class in an array

[rian bron]

Hello guys, i wrote a code who creates a new city if there is place available inside an array.
now i want to enter one of the values of the City class to determine which this.value is the highest among the array inputs:

import java.util.Scanner;
public class Array
{

    public static void main(String[]args)
    {
        Scanner scan=new Scanner(System.in);
        City[] ci=new City[3];
        
        for( int i=0;i<3;i++)
        {  
            System.out.println("Enter city Name: ");
            String cityName=scan.nextLine();
            System.out.println("Enter center X");
            double centerx=scan.nextDouble();
            System.out.println("Enter center y");
            double centery=scan.nextDouble();
            Point cityCenter=new Point(centerx,centery);
            System.out.println("Enter central X");
            double centralx=scan.nextDouble();
            System.out.println("Enter central Y");
            double centraly=scan.nextDouble();
            Point centralStation=new Point (centralx,centraly);
            System.out.println("Enter number of residents");
            int numOfResidents=scan.nextInt();
            System.out.println("Enter number of neighborhoods");
            int numOfNeighborhoods=scan.nextInt();
            scan.nextLine();

            City number=new City(cityName,cityCenter,centralStation,numOfResidents,
                    numOfNeighborhoods);

            
        }
        for( int j=0;j<3;j++)
        {
            System.out.println(ci[j]);
        }
        
    }
}

but I don't know how to point to a variable in other class inside the array , i tried doing:

int max_residents=ci[0].numbernumOfResidents;

but it says " can't find variable number"

do you have a solution?

thank you

[rian bron]

+ why does the method returns null?

[Knute Snortum]

I suspect the problem is here:
           City number=new City(cityName,cityCenter,centralStation,numOfResidents,                    numOfNeighborhoods); Here you are creating a new variable "number" that is of type City.  I suspect what you want is to put the new City into the array ci, right?  To do this follow this pattern: ci[index] = value; In this case, i is the index and new City(... is the value.

[rian bron]

Knute Snortum wrote:I suspect the problem is here:
           City number=new City(cityName,cityCenter,centralStation,numOfResidents,                    numOfNeighborhoods); Here you are creating a new variable "number" that is of type City.  I suspect what you want is to put the new City into the array ci, right?  To do this follow this pattern: ci[index] = value; In this case, i is the index and new City(... is the value.

yeah i figure why this return null , right after i posted the post.

but still , i need to find an answer to how to point to a City variable inside the array?

lets say i want to initialize a variable called max_resident as int to be equals to the numOfResidents in the first City object inside the array.
how can i do that?

Thank you

[Fred Kleinschmidt]

That depends on how the City class is written. Is numOfResidents a public variable (hopefully not), or is it a private variable with a public getter method, such as getNumOfResidents() ?

[rian bron]

Fred Kleinschmidt wrote:That depends on how the City class is written. Is numOfResidents a public variable (hopefully not), or is it a private variable with a public getter method, such as getNumOfResidents() ?

i didn't want to write a long code so i set this variable as  public and not private.

but can you show me the way to approach the variable who set as public variable
and i will try to show you later how to approach the same variable that i will set to private ?

thank you

[Paul Clapham]

So you want to get the value of a public variable of an object?

1. Get a reference to the object and assign it to a variable:

City city = // your code which gets a reference to the City object you had in mind;

2. Use that reference to get the value of the public variable:

int result = city.numOfResidents;

This is assuming your public variable is called "numOfResidents" -- you still didn't show us your City class.

[rian bron]

Paul Clapham wrote:So you want to get the value of a public variable of an object?

1. Get a reference to the object and assign it to a variable:

City city = // your code which gets a reference to the City object you had in mind;

2. Use that reference to get the value of the public variable:

int result = city.numOfResidents;

This is assuming your public variable is called "numOfResidents" -- you still didn't show us your City class.

I think you didn't understand me ,
i know how to point a local variable from the class itself , i don't know how to point a local variable from a class in an array.

i can't say City city because my City object doesn't have a name because it is created inside a loop.
i can only reach it by saying ci[0], ci[1],ci[2]...

and i'm asking how can i reach the local variable from the City class *inside* the array ?

the variable in the City class is set to private
and there is  a getter method in the City class that returns value of this variable

I tried logically to say :

int max_residents=ci[0].numOfResidents;

but i think its wrong


and the city class isn't that important , there is more than 300 lines of code over there and it's really long so i don't want to share it ..
but it consists a private  variable called numOfResidents inside the public class , and a constructor of this class which initialize this variable  

[rian bron]

rian bron wrote:

Paul Clapham wrote:So you want to get the value of a public variable of an object?

1. Get a reference to the object and assign it to a variable:

City city = // your code which gets a reference to the City object you had in mind;

2. Use that reference to get the value of the public variable:

int result = city.numOfResidents;

This is assuming your public variable is called "numOfResidents" -- you still didn't show us your City class.

I think you didn't understand me ,
i know how to point a local variable from the class itself , i don't know how to point a local variable from a class in an array.

i can't say City city because my City object doesn't have a name because it is created inside a loop.
i can only reach it by saying ci[0], ci[1],ci[2]...

and i'm asking how can i reach the local variable from the City class *inside* the array ?

the variable in the City class is set to private
and there is  a getter method in the City class that returns value of this variable

I tried logically to say :

int max_residents=ci[0].numOfResidents;

but i think its wrong


and the city class isn't that important , there is more than 300 lines of code over there and it's really long so i don't want to share it ..
but it consists a private  variable called numOfResidents inside the public class , and a constructor of this class which initialize this variable  

I think i figured it out, i wrote :

int max_residents=ci[0].getNumOfResidents();

and i get no compile error so i think  this should work.

how to i point at a variable of an object from  the array that is set to public and not private ?

[Knute Snortum]

how to i point at a variable of an object from  the array that is set to public and not private ?

What have you tired?  Look to what you've already learned.

[Paul Clapham]

rian bron wrote:I think i figured it out, i wrote :

int max_residents=ci[0].getNumOfResidents();

and i get no compile error so i think  this should work.

how to i point at a variable of an object from  the array that is set to public and not private ?

Yes, that's what I told you. Get a reference to the object -- for some reason you seem to think that it's controversial for an array element to be an object reference, but as you see that's a perfectly ordinary thing. Then call the method, or access the variable if it's public.

I already told you how to access a public variable of an object, too. You should be able to figure out how to write that if the reference to the object happens to be an array element.