Urgent:Why output different in String and class?Why different behavior?

amit_gupta14

We know there are 2 categories of datatypes in C#: Value type and reference type String and Class both are refernce types. I have made 2 program in C# using each of them but got different outputs. Code using String: string s1="amit"; string s2=s1; Console.WriteLine("Before s1={0}",s1);//Output is: amit Console.WriteLine("Before s2={0}",s2);//Output is: amit s2="shilpi"; Console.WriteLine("After s1={0}",s1);//Output is: amit Console.WriteLine("After s2={0}",s2);//Output is: shilpi ---------------------------------------------------------------------- Code using Class: using System; class class1 { private int num; public int Num { get { return num; } set { num=value; } } } class mainclass { public static void Main() { class1 c1=new class1(); class1 c2=new class1(); c1.Num=100; c2=c1; Console.WriteLine("Before c1={0}",c1.Num);//output is 100 Console.WriteLine("Before c2={0}",c2.Num);//output is 100 c2.Num=200; Console.WriteLine("After c1={0}",c1.Num);//output is 200 Console.WriteLine("After c2={0}",c2.Num);//output is 200 } } ---------------------------------------------------------------------- In string case: when s2 is changed, s1 is not affected In Class case: when c2.value is changed, c1.value is also changed Why their behaviour is different?

6 Replies

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Mykonine22y ago
When you use s2 = s1 you are assigning s2 to refer to the same string as s1. However... When you use s1 = "shilpi" you are essentially saying s1 = new string("shilpi"); that is, when you assign to s1 you're creating a new string object (a new character array). I'm not 100% sure of this, but I believe the string class is immutable; that is, every time you change a string a new string is instantiated. When you use c2 = c1, again they refer to the same object. However... The object that they refer to contains a reference to another object. When you said c2.Num = 200, you were assigning the number referred to by class1, but you did not create a new instance of class1, which means that c1 and c2 still refer to the same object, which was not the case with s1 and s2.
robin 022y ago
Ok. Thanks.
bilnaad22y ago
lol example should be namespace csConsole { using System; class SomeClass { public int Value; } class MessageTest { public static void Change(SomeClass c) { c.Value = 155; } public static void ChangeWrong(SomeClass c) { SomeClass sc = new SomeClass(); sc.Value = -1; c = sc;//forgot to add this one :) } public static void Main() { SomeClass sc = new SomeClass(); sc.Value = 255; Change(sc); Console.WriteLine( sc.Value ); ChangeWrong(sc); Console.WriteLine( sc.Value ); Console.Read(); } } }
bilnaad22y ago
Robin? What kanan wrote is the absolute truth :) When you copy a reference in another variable the copy will remain untill you assign to that variable. Example: namespace csConsole { using System; class SomeClass { public int Value; } class MessageTest { //reference remains public static void Change(SomeClass c) { c.Value = 155; } //reference will be gone public static void ChangeWrong(SomeClass c) { SomeClass sc = new SomeClass(); sc.Value = -1; } public static void Main() { SomeClass sc = new SomeClass(); sc.Value = 255; Change(sc);//good Console.WriteLine( sc.Value ); ChangeWrong(sc);//bad Console.WriteLine( sc.Value ); Console.Read(); } } }
robin 022y ago
I was always thinking, that '=' operator of string class is making clone of string, and not just applies reference..... And if you need the same behavior from your own class - override '=' operator. Am I wrong?
eyes22y ago
Hi, String is an reference type, No doubt . . . When U assign "amit" to s1, "amit" is stored in a memory and s1 refers to that memory . . . When U assign s1 to s2, s2 also refers to the same memory . . . So now that output are same . . . When U assign "shilpi" to s1, "shipi" is stored in new memory and s1 now refers to this memory, but s2 still refers to the old memory . . . So now the output are not same . . . Class is also reference . . . When U instantiate c1 and c2, two refers to different class1 object . . . When U assign c1 to c2, both refers to same class1 object, particularly c1 . . . Since both refers same object, output is 200 after the value is change thru c2 . . . Hope U got little . . . Cheers, Kanna . . .