fast deep copy

[Lucas Smith]

Hi.

I have to create a deep copy of an object [Space2D instance].

public class Space2D extends Space {
	private Cell[][] cells;
	private final int X_SIZE, Y_SIZE;
	private int X_SIZE_REAL, Y_SIZE_REAL;    
.
.
.

public class Cell {
	public double orientation, dislocations;
	public boolean nucleon, onBoundary, recrystallized;
.
.
.

That copying will be critical for the performance of the application.

What is the best way to create a deep copy in a fast way?

Thanks!

[Rob Spoor]

There is no fast way. The fastest way is to simply iterate over the array (so a nested loop), then duplicating each cell.

public class Space2D extends Space implements Cloneable {   
    private Cell[][] cells;   
    private final int X_SIZE, Y_SIZE;   
    private int X_SIZE_REAL, Y_SIZE_REAL;       

    public Space2D clone() { // ignoring the exception
        Space2D clone = (Space2D)super.clone();
        clone.cells = cells.clone();
        for (int i = 0; i < clone.cells.length; i++) {
            clone.cells[i] = clone.cells[i].clone();
            for (int j = 0; j < clone.cells[i].length; j++) {
                clone.cells[i][j] = clone.cells[i][j].clone();
            }
        }
        return clone;
    }
}
  
public class Cell implements Cloneable {   
    public double orientation, dislocations;   
    public boolean nucleon, onBoundary, recrystallized;  

    public Cell clone() { // again, ignoring the exception
        return (Cell)super.clone(); // good if all fields are primitives / immutable
    }
}

[Seetharaman Venkatasamy]

Lucas Smith wrote:What is the best way to create a deep copy in a fast way?

copy constructor?

[Rob Spoor]

Also an option. Code similar to mine can be used inside the constructor.

[Seetharaman Venkatasamy]

Rob Prime wrote:Code similar to mine can be used inside the constructor.

yes, but we can avoid the clone

[Campbell Ritchie]

Have you tried a copy constructor? Note 5 of your 6 fields are primitives, so copying them is very fast.

For the Cell[][] array of arrays, you would have to copy each element of the included arrays, then copy those components into a new array. You can try the clone() method on each component (Cell[]) array, copying them into a new Cell[][] array, or the System#arraycopy(java.lang.Object, int, java.lang.Object, int, int) method. If you use a for loop, remember it won't work in a for-each loop.
If the Cell objets are mutable, you may need to take a copy or clone() of each Cell object, too.

Try the System#nanoTime() method before and after 1000000 copying operations with arraycopy and clone.

[Seetharaman Venkatasamy]

Campbell Ritchie wrote:Have you tried a copy constructor?

It works for me

   

class Hie
{
		
	String str;
	StringBuffer[][] buffer;
	
	Hie(String str, StringBuffer[][] buffer)
	{
		this.str = str;
		this.buffer = buffer;
	}
               //copy constructor
	Hie(Hie h)
	{
		this.str = h.str;
		this.buffer =h. buffer;
	}
	
}


public class Test 
{ 
	
	public static void main(String... args)   
	{   
		try
		{
			StringBuffer[] a = {new StringBuffer("1"),new StringBuffer("2")};
			StringBuffer[][] buffer = {a};
			Hie h = new Hie("A", buffer);
			System.out.println(h.str + " and "+Arrays.deepToString(h.buffer));
			Hie i = new Hie(h);
			System.out.println(i.str + " and "+Arrays.deepToString(i.buffer));
			
		}
		catch(Exception ex)
		{
			ex.printStackTrace();
		}

	}   
}   

[Lucas Smith]

Thank you all.
Rob's suggestion will be good .

[Rob Spoor]

Seetharaman, that copy constructor doesn't perform a deep copy; the StringBuffer[][] will be shared. Try the following:

public class Test
{
    public static void main(String... args)
    {
        StringBuffer[] a = {new StringBuffer("1"),new StringBuffer("2")};
        StringBuffer[][] buffer = {a};
        Hie h = new Hie("A", buffer);
        System.out.println(h.str + " and "+Arrays.deepToString(h.buffer));
        Hie i = new Hie(h);
        System.out.println(i.str + " and "+Arrays.deepToString(i.buffer));
        // now modify a
        a[0].append("345");
        a[1] = null;
        // and print
        System.out.println(h.str + " and "+Arrays.deepToString(h.buffer));
        System.out.println(i.str + " and "+Arrays.deepToString(i.buffer));
    }
}

Not what you want, is it?

[Seetharaman Venkatasamy]

Rob Prime wrote:Not what you want, is it?

Thanks rob, you are right! now I get that point.

[Rob Spoor]

You're welcome.