NP95 shallow copy/deep copy

Question

Hi Guys

If

p3: X: 100 Y: 100

p4: X: 100 Y: 100

I mean this is shallow copy

If

p3: X: 100 Y: 100

p4: X: 0 Y: 100

I mean this is deep copy

That means if p3 is independent of p4 it is a deep copy

In this program MemberwiseClone() is producing deep copy.

I wish to know whether my understanding is correct.

Please explain.

Thank you

using System;

// The Point class supports deep copy semantics a la ICloneable.

public class Point : ICloneable

{

public int x, y;

public Point(int x, int y)

{

this.x = x;

this.y = y;

}

// Return a copy of the current object.

public object Clone()

{

// Copy each field of the Point member by member.

return this.MemberwiseClone();

}

public override string ToString()

{

return "X: " + x + " Y: " + y;

}

public class CloneDemo

{

public static void Main()

{

// Notice Clone() returns a generic object type.

// You must perform an explicit cast to obtain the derived type.

Point p3 = new Point(100, 100);

Point p4 = (Point)p3.Clone();

// Change p4.x (which will not change p3.x).

p4.x = 0;

// Print each object.

Console.WriteLine("p3: {0}", p3);

Console.WriteLine("p4: {0}", p4);

}

/*

p3: X: 100 Y: 100

p4: X: 0 Y: 100

*/

Maha · Answer

Thank you Alan.

Alan · Answer

Well as Manish said a compound object is an object which contains other objects. If we take the narrow definition of object (i.e. a reference type instance created on the heap) then a Point object (as modified) is a compound object because it contains a Color object. The latter is also a compound object because it contains a string object.

Maha · Answer

What is meant by compound objects ? In my understanding compound objects in the above program is p4.c.Name = Blue ;. Because this code contains more than one object. I wish to know whether my understanding is correct. Please explain.

Alan · Answer

This modifed version now includes a reference type field of type Color: using System; public class Color { public string Name; public Color (string name) { Name = name; } } // The Point class supports deep copy semantics a la ICloneable. public class Point : ICloneable { public int x y; public Color c; public Point(int x int y Color c) { this.x = x; this.y = y; this.c = c; } // Return a copy of the current object. public object Clone() { // Copy each field of the Point member by member. return this.MemberwiseClone(); } public override string ToString() { return X:  + x +  Y:  + y + C:  + c.Name; } } public class CloneDemo { public static void Main() { // Notice Clone() returns a generic object type. // You must perform an explicit cast to obtain the derived type. Point p3 = new Point(100 100 new Color(Red)); Point p4 = (Point)p3.Clone(); // change p4.c.Name which will change p3.c.Name as it's the same Color object p4.c.Name = Blue; // Print each object. Console.WriteLine(p3: {0} p3); Console.WriteLine(p4: {0} p4); // Change p4.c which will not change p3.c as it's a different Color object p4.c = new Color(Green); // Print each object again. Console.WriteLine(); Console.WriteLine(p3: {0} p3); Console.WriteLine(p4: {0} p4); } }

Maha · Answer

It is much appreciated if you modify the above program that supports compound objects .

Manish Dwivedi · Answer

Hi Friend. The difference between shallow and deep copying is only relevant for compound objects (objects that contain other objects like lists or class instances): A shallow copy constructs a new compound object and then (to the extent possible) inserts references into it to the objects found in the original. A deep copy constructs a new compound object and then recursively inserts copies into it of the objects found in the original. Happy Coding!!