OOPS interview questions

What is the difference between the destructor and the Finalize() method? When does the Finalize() method get called?
Finalize() corresponds to the .Net Framework and is part of the System.Object class. Destructors are C#'s implementation of the Finalize() method. The functionality of both Finalize() and the destructor is the same, i.e., they contain code for freeing the resources when the object is about to be garbage collected. In C#, destructors are converted to the Finalize() method when the program is compiled. The Finalize() method is called by the .Net Runtime and we can not predict when it will be called. It is guaranteed to be called when there is no reference pointing to the object and the object is about to be garbage collected.

Garbage Collection

·       <!--[if !supportLists]--> Garbage collection is the mechanism that reclaims the memory resources of an object when it is no longer referenced by a variable.<!--[endif]-->

·       <!--[if !supportLists]--> .Net Runtime performs automatically performs garbage collection, however you can force the garbage collection to run at a certain point in your code by calling System.GC.Collect().<!--[endif]-->

·       <!--[if !supportLists]--> Advantage of Garbage collection : It prevents programming error that could otherwise occur by incorrectly deleting or failing to delete objects.<!--[endif]-->

Enumeration

Enumeration improves code readability. It also helps in avoiding typing mistake.

Concept of Heap and Stack

Local Variables	Stack
Free Memory (Larger Memory Area than Stack).	Heap
Global Variables	Permanent Storage area
Program Instruction

The Program Instruction and Global and Static variables are stored in a region known as permanent storage area and the local variables are stored in another area called stack. The memory space located between these two regions is available for dynamic memory allocation during execution of program. This free memory region is called heap. The size of heap keeps on changing when program is executed due to creation and death of variables that are local to functions and blocks. Therefore, it is possible to encounter memory “overflow” during dynamic allocation process.

<!--[if !supportLineBreakNewLine]--> <!--[endif]-->

Value Type and Reference Type

A variable is value type or reference type is solely determined by its data type.

Eg: int, float, char, decimal, bool, decimal, struct, etc are value types, while object type such as class, String, Array, etc are reference type.

Value Type

<!--[if !supportLists]--> As name suggest Value Type stores “value” directly.<!--[endif]-->

<!--[if !supportLists]--> For eg: <!--[endif]-->

<!--[if !supportLists]--> //I and J are both of type int<!--[endif]-->

<!--[if !supportLists]--> I = 20;<!--[endif]-->

<!--[if !supportLists]--> J = I;<!--[endif]-->

<!--[if !supportLists]--> int is a value type, which means that the above statements will results in two locations in memory.<!--[endif]-->

<!--[if !supportLists]--> For each instance of value type separate memory is allocated.<!--[endif]-->

<!--[if !supportLists]--> Stored in a Stack.<!--[endif]-->

<!--[if !supportLists]--> It Provides Quick Access, because of value located on stack.<!--[endif]-->

Reference Type

<!--[if !supportLists]--> As name suggest Reference Type stores “reference” to the value.<!--[endif]-->

<!--[if !supportLists]--> For eg: <!--[endif]-->

<!--[if !supportLists]--> Vector X, Y; //Object is defined. (No memory is allocated.)<!--[endif]-->

<!--[if !supportLists]--> X = new Vector(); //Memory is allocated to Object. //(new is responsible for allocating memory.)<!--[endif]-->

<!--[if !supportLists]--> X.value = 30; //Initialising value field in a vector class.<!--[endif]-->

<!--[if !supportLists]--> Y = X; //Both X and Y points to same memory location. //No memory is created for Y.<!--[endif]-->

<!--[if !supportLists]--> Console.writeline(Y.value); //displays 30, as both points to same memory<!--[endif]-->

<!--[if !supportLists]--> Y.value = 50;<!--[endif]-->

<!--[if !supportLists]--> Console.writeline(X.value); //displays 50.<!--[endif]-->

<!--[if !supportLists]--> Note: If a variable is reference it is possible to indicate that it does not refer to any object by setting its value to null;<!--[endif]-->

<!--[if !supportLists]--> Reference type are stored on Heap.<!--[endif]-->

<!--[if !supportLists]--> It provides comparatively slower access, as value located on heap.<!--[endif]-->

ref keyword

Passing variables by value is the default. However, we can force the value parameter to be passed by reference. Note: variable “must” be initialized before it is passed into a method.

out keyword

out keyword is used for passing a variable for output purpose. It has same concept as ref keyword, but passing a ref parameter needs variable to be initialized while out parameter is passed without initialized.

It is useful when we want to return more than one value from the method.

Note: You must assigned value to out parameter in method body, otherwise the method won’t compiled.