Csharp/C Sharp/Class Interface/Object Instance

Calling a Class Method on a Class

using System;
public class MainClass {
    public static void Main() {
        string firstName = "J";
        string lastName = "R";
        string name = string.Format("{0} {1}", firstName, lastName);
        Console.WriteLine(name);
    }
}

Calling an Instance Method on an Object

using System;
public class MainClass {
    public static void Main() {
        string name = "Joe";
        Console.WriteLine(name.ToUpper());
    }
}

Catch NullReferenceException Exception

using System;
class MyClass {
    public int Value;
}
class MainClass {
    public static void Main() {
        try {
            MyClass MyObject = new MyClass();
            MyObject = null;
            MyObject.Value = 123;
        } catch (NullReferenceException) {
            Console.WriteLine("Cannot reference a null object.");
        }
    }
}

Object assignment

 

using System;
public class Foo
{
    public int i;
}
   
class RefTest1App
{
    static void Main(string[] args)
    {
        Foo test1 = new Foo();
        test1.i = 1;
   
        Foo test2 = new Foo();
        test2.i = 2;
   
        Console.WriteLine("BEFORE OBJECT ASSIGNMENT");
        Console.WriteLine("test1.i={0}", test1.i);
        Console.WriteLine("test2.i={0}", test2.i);
        Console.WriteLine();
   
        test1 = test2;
   
        Console.WriteLine("AFTER OBJECT ASSIGNMENT");
        Console.WriteLine("test1.i={0}", test1.i);
        Console.WriteLine("test2.i={0}", test2.i);
        Console.WriteLine();
   
        test1.i = 42;
   
        Console.WriteLine("AFTER CHANGE TO ONLY TEST1 MEMBER");
        Console.WriteLine("test1.i={0}", test1.i);
        Console.WriteLine("test2.i={0}", test2.i);
    }
}

Object.ReferenceEquals Method

 
using System;

public class Starter {
    public static void Main() {
        Employee obj1 = new Employee(5678);
        Employee obj2 = (Employee)obj1.Clone();
        if (Employee.ReferenceEquals(obj1, obj2)) {
            Console.WriteLine("objects identical");
        } else {
            Console.WriteLine("objects not identical");
        }
    }
}
class Employee : ICloneable {
    public Employee(int id) {
        if ((id < 1000) || (id > 9999)) {
            throw new Exception(
                "Invalid Employee ID");
        }
    }
    public object Clone() {
        return MemberwiseClone();
    }
}

Pass by ref for object parameters

 

using System;
using System.Collections.Generic;
using System.Text;
class Pass {
    public static void Value(ref int param) {
        param = 42;
    }
    public static void Reference(WrappedInt param) {
        param.Number = 42;
    }
}
class WrappedInt {
    public int Number;
}
class Program {
    static void Entrance() {
        int i = 0;
        Console.WriteLine(i);
        Pass.Value(ref i);
        Console.WriteLine(i);
        WrappedInt wi = new WrappedInt();
        Console.WriteLine(wi.Number);
        Pass.Reference(wi);
        Console.WriteLine(wi.Number);
    }
    static void Main(string[] args) {
        try {
            Entrance();
        } catch (Exception ex) {
            Console.WriteLine(ex.Message);
        }
    }
}

Point object

 
using System;
using System.Collections.Generic;
using System.Text;
class Point {
    public Point() {
        this.x = -1;
        this.y = -1;
        objectCount++;
    }
    public Point(int x, int y) {
        this.x = x;
        this.y = y;
        objectCount++;
    }
    public double DistanceTo(Point other) {
        int xDiff = this.x - other.x;
        int yDiff = this.y - other.y;
        return Math.Sqrt((xDiff * xDiff) + (yDiff * yDiff));
    }
    public static int ObjectCount() {
        return objectCount;
    }
    private int x, y;
    private static int objectCount = 0;
}
class Program {
    static void Main(string[] args) {
        try {
            Point origin = new Point();
            Point bottomRight = new Point(1024, 1280);
            double distance = origin.DistanceTo(bottomRight);
            Console.WriteLine("Distance is {0}", distance);
            Console.WriteLine("No of Point objects: {0}", Point.ObjectCount());
        } catch (Exception ex) {
            Console.WriteLine(ex.Message);
        }
    }
}