[SOLVED] Deep copy

[thorne_]

Hi,

Im trying to clone a list of objects in my application.

this is the object hierarchy

public class M implements Cloneable, java.io.Serializable {
 
	private static final long serialVersionUID = 1L;
 
	private List<S> s;
	private Map<String, Object> parameters;//getters included, sniped
	
	 @Override
	public Object clone() {
		try {
		  return super.clone();
		} catch (CloneNotSupportedException ex) {
		  System.out.println("Cloning of M failed");
		      throw new InternalError(ex.toString());
		   }
	  }
	
}

this class includes a list of this class

public class S implements Cloneable, java.io.Serializable {
 
	private static final long serialVersionUID = 1L;
	
	private Map<String, Object> parameters;
	
	
	 @Override
	public Object clone() {
			try {
			  return super.clone();
			} catch (CloneNotSupportedException ex) {
			  System.out.println("Cloning of Sfailed");
			      throw new InternalError(ex.toString());
			   }
		  }
}

In my application i create an set of class M objects, each containing a list of S objects. This set only has default parameters. i need to be able to grab a copy of this set and modify it without effecting the original contents - this is why i implemented cloneable.

This is my attempt to do this :

class ObjectDao{
 
private static ArrayList<M> allMs = new ArrayList<M>();
 
private void addM(M m){
allMs.add(m);
}
 
private static ArrayList<M> getClonedMList(){
		
		ArrayList<M> clonedMs = new ArrayList<M>();
		
		try {
			
			for( int i = 0;i < allMs.size();i++ ) {
			
				M clonedM = (M)allMs.get(i).clone();
				
				clonedM.setParameters( (HashMap) 
						( (HashMap) allMs.get(i).getParameters() ).clone() );
			
				
				for(int j = 0;j < ( allMs.get(i).getSs().size() );j++) {
				
					S clonedS= (S) allMs.get(i).getSs().get(j).clone();
						
					clonedS.setParameters( (HashMap)
							( (HashMap) allMs.get(j).getSs().get(i).getParameters() ).clone() );
					
					clonedM.getSs().set(j, clonedS);
						
				}
				
				clonedMs.add(clonedM);
				
			}
			
		}
		catch (Exception e) {
			log.error(e.toString());
		}
		
		
		return clonedMs;
		
	}

I clone each object with the parent object individually but it doesnt have the desired effect i.e. if i modify an S's parameters (on an M received from this method) somewhere else in the application the next call to this method returns objects with the modified parameters instead of the original state

Can anybody help?

[makpandian]

i think you have to read about how to ask questions gently?

[OrangeDog]

Your clone() methods have to work through your lists and maps and deep copy them too. super.clone() just performs a shallow copy of the the outer object.

[thorne_]

Is serialising and then deserialising an object the only way of performing a deep copy?

This is simply too slow for what i need

[OrangeDog]

Not at all. Usually you just have to iterate through everything. Serialisation is for serialising things, not cloning them.

public class Example implements Cloneable {
    private Cloneable[] array;
    Map<String,Cloneable> map;
    int primitive;
    Cloneable object;

    public Example clone() {
        Example clone = new Example();

        clone.primitive = this.primitive;
        clone.object = this.object.clone();

        clone.array = new Cloneable[this.array.length];
        for (int i=0; i<array.length; i++) {
            clone.array[i] = this.array[i].clone();
        }

        clone.map = new Map<String,Cloneable>();
        for (String s : map.getKeys()) {
            clone.map.put(s, this.map.get(s).clone());
        }

        return clone;
    }
}

Note that Strings, and other immutable objects, don't need cloning.

[thorne_]

thanks alot