How to create and store multiple instances of objects?

[Zigster]

What I am trying to do, is to create several hundred instances of an object that return random int values.

For instance, say I want to create a car store, and have 50 cars available to buy, with different stats for things like, top speed, price, fuel consumption, etc, for each car.

I can create a class for a car that returns random numbers, but how do I create multiple instances of a car all at once and store the info so they can be referenced? I know you can instantiate a class with "new", but how do I do that several hundred times at once? Do I use a loop? And how can I store the info, in an array?

I'm having trouble finding any examples or tutorials of what I want to do and would really appreciate some guidance.

Cheers!

[JosAH]

Suppose a Car object takes care of its own random values, a simple loop can do the job:

List<Car> cars= new ArrayList<Car>();
for (int i= 0; i < nofCarsWanted; i++)
   cars.add(new Car());

kind regards,

Jos

[Zigster]

Thanks JosAH! That's exactly what I wanted, it's much easier than I thought it would be.

Edit: Actually I just have a question about something in my code:

package Main;

import java.util.Random;

public class Car {
	
	Random generator = new Random();	
		
	int topspeed = generator.nextInt(10) + 1;{       //What are these parenthesise for?
	System.out.println(toString());
	}                                            //If I don't have them I get an error?
		
	public String toString(){
	return "Top Speed: " + topspeed; 
	}
}

[JosAH]

Those curly brackets embrace an initialization block (a simple System.out.println( ... ) statement here); personally I find the placement of those brackets obstrusive and above all: you don't need that System.out.println( ... ) statement; I'd remove everything between those brackets including the brackets.

kind regards,

Jos

[Zigster]

How can I print out the topspeed of the Car objects then?

[JosAH]

How can I print out the topspeed of the Car objects then?

Simply print a Car object and its toString() method will do the rest; try it.

kind regards,

Jos

[Zigster]

When do I print the Car object? It gives me an error if I try to use: System.out.println(Car); either in my Main class or my Car class. It gives me this error:

Syntax error on token "Car", VariableDeclaratorId expected after this token

I tried: System.out.println(cars) in my Main class and it prints out the Array list, it prints it out like this: [Top Speed: 5, Top Speed: 7, Top Speed: 5, Top Speed: 8] (of course it's longer but just an example) and I can't seem to format it with + "\n" or anything. I want to print out each Car on a new line though.

Edit: Ok, not sure what I was doing before but \n does work, but not sure how to get ride of the [], and would still like to know how to print an object with a toString statement.

[Diargg]

int a=3;
System.out.println(a);    // Prints out "3"
Car chevy = new Car();
System.out.println(chevy);    //Prints out chevy.toString();

You've tried to print out the Array, not the Cars inside of it. Perhaps there's a way of accessing individual members of an Array?

[Zigster]

Thanks Diargg, this is my Main class now:

package Main;

import java.util.ArrayList;
import java.util.List;

public class Main {
	
	public static void main (String[] args){
		
		List<Car> cars= new ArrayList<Car>();
		for (int i= 0; i < 50; i++){
			cars.add(new Car());
			Car item = cars.get(i);
			System.out.println("Model Number: " + (i+1) + " \t" + item);
		}
	}
}

And it prints:

Model Number: 1 Top Speed: 10 Accelerations: 1 Braking: 8 Handling: 2 Price: 14
Model Number: 2 Top Speed: 8 Accelerations: 8 Braking: 10 Handling: 6 Price: 21
Model Number: 3 Top Speed: 9 Accelerations: 9 Braking: 10 Handling: 5 Price: 25
Model Number: 4 Top Speed: 9 Accelerations: 7 Braking: 9 Handling: 8 Price: 19

[Norm]

It seems wasteful to put something into an arraylist and immediately retrieve it:

        for (int i= 0; i < 50; i++){
            cars.add(new Car());
            Car item = cars.get(i);
            System.out.println("Model Number: " + (i+1) + " \t" + item);
        }

vs

        for (int i= 0; i < 50; i++){
            Car item = new Car();   // create a Car object
            cars.add(item);             // add to list
            System.out.println("Model Number: " + (i+1) + " \t" + item);  // print it
        }