Print values of ArrayList instead of classname

Question

I'd like to print all ten random generated points for each object in the ArrayList AL.

public class Point
    {
        public int x;
        public int y;
    
        public Point(int x, int y)
        {
            x = this.x;
            y = this.y;
        }
        
    }    

public class ArrayListTest
    {
        public static void Main(string[] args)
        {
            ArrayList AL = new ArrayList();
            Random Rnd = new Random();
            for (int i = 1; i <= 10; i++)
            {
                Point p = new Point(Rnd.Next(50), Rnd.Next(50));
                AL.Add(p);            
            }
    
        PrintValues(AL);
        }
    
        public static void PrintValues(IEnumerable myList)
        {
            
            foreach (Object obj in myList)
                Console.WriteLine("{0} ", obj);
        }
    }

Output on console:

Point 
Point 
Point 
Point 
Point 
Point 
Point 
Point 
Point 
Point

My Problem is, that the classname of the object printed and not the values of the objects. I am using .NET Framework v4.8

First of all, do not use an ArrayList, use a List. Secondly, override ToString() to print the x and y — insane_developer, Oct 21 '20 at 15:30
Please show us your `Point` class, or confirm that you are using `System.Drawing.Point`. Your code works fine if using `System.Drawing.Point`. — Matthew Watson, Oct 21 '20 at 15:34
Alternatively to answers given, you could consider using [Point Struct](https://learn.microsoft.com/en-us/dotnet/api/system.drawing.point?view=netframework-4.8) instead of your own Point class. — Fildor, Oct 21 '20 at 15:47
You have your X and Y assignments in the constructor going in the wrong direction. — Matthew Watson, Oct 21 '20 at 15:49

Matthew Watson · Accepted Answer · 2020-10-21T15:53:16.260

(Aside: I recommend that you don't define your own class called Point. It's likely to conflict with a built-in class and cause confusion. You should give your class a different name.)

So, what happens when you do Console.WriteLine(object obj) is that inside Console.WriteLine() it ends up calling object.ToString() to determine the string to write.

By default, if you don't write your own implementation of ToString(), it will return the name of the class - this is why you are seeing Point in the output.

Since you are writing your own Point class, you can override its ToString() to return a formatted string. This is the best solution.

Assuming that your Point class has X and Y values, you can do that by adding the following to the class:

public override string ToString()
{
    return $"X={x}, Y={y}";
}

If you didn't want to do this (or supposing it was a third-party class that you couldn't change), you would have to format the string explicitly before passing it to Console.WriteLine().

Unfortunately, because you are using ArrayList, you end up with only an object - so in order to format it you will need to cast it to the correct type in order to get at its X and Y values:

foreach (Object obj in myList)
{
    Point p = (Point)obj;
    Console.WriteLine("X={0}, Y={1}", p.x, p.y);
}

Or you can take advantage of the fact that a foreach for an IEnumerable will do the cast for you if you declare the loop variable as the correct type:

foreach (Point p in myList)
{
    Console.WriteLine("X={0}, Y={1}", p.x, p.x);
}

However, much better is to use List<Point> rather than an ArrayList - then the elements will be of type Point:

static class Program
{
    public static void Main(string[] args)
    {
        List<Point> AL  = new List<Point>();
        Random      Rnd = new Random();
        for (int i = 1; i <= 10; i++)
        {
            Point p = new Point(Rnd.Next(50), Rnd.Next(50));
            AL.Add(p);
        }

        PrintValues(AL);
    }

    public static void PrintValues(IEnumerable<Point> myList)
    {
        foreach (var p in myList)
        {
            Console.WriteLine("X={0}, Y={1}", p.x, p.x);
        }
    }
}

As a final note, you might want to consider using the System.Drawing.Point or System.Windows.Point struct rather than rolling your own Point class.

score 0 · Answer 2 · answered Oct 21 '20 at 15:31

You aren't using generic collections, which would be more ideal here. But because you are not, you are working with objects. The default ToString implementation on an object will return the name of the object. You'll need to cast your object back to a Point type to work with it.

This is one way to cast the object back to a point

public static void PrintValues(IEnumerable myList)
{
    
    foreach (var point in myList.Cast<Point>())
        Console.WriteLine($"{obj.X} {obj.Y}");
}

@Fildor Point class is added in the question. – DerDave Oct 21 '20 at 15:43 — DerDave, Oct 21 '20 at 15:43

Print values of ArrayList instead of classname

2 Answers2