Thread: Beginner Problem

Hi, I'm a little confused with an assignment. I've try to figure it out for a while but I'm stuck.

The instructions are as follows:

Make 2 classes WrapperShallow and WrapperDeep.

Each class is simply a wrapper class to hold a private array variable. int [] a;
The default constructor for each class should initialize “a”.
Each class should have a toString() and equals().
Each class should have a setArray method that allows you to set the “a” variable.

WrapperShallow should have an invalid copy constructor.

public WrapperShallow(WrapperShallow ws){
a = ws.a;
}

WrapperDeep should have a properly functioning copy constructor.

public WrapperDeep(WrapperDeep ws){
a = new int[3];
for(int i = 0; i < 3; i++)
a[i]=ws.a[i];
}

Think about why shallow is wrong and deep is correct! What happens to the old “a” in the WrapperDeep copy constructor? (think garbage collection)

Example Output:

--------------------Configuration: <Default>--------------------

**** TESTING SHALLOW OBJECTS ****

inital shallow object contains
7 17 77
copy shallow object contains
7 17 77
inital shallow object changed to
13 14 15
copy shallow object not changed contains
13 14 15
WOOPS! ws.equals(ws2) is true

**** TESTING DEEP OBJECTS ****

inital deep object contains
2 3 4
copy deep object contains
2 3 4
inital deep object changed to
7 6 -5
copy deep object not changed contains
2 3 4
RIGHT! wd.equals(wd2) is false

Process completed.


So far I have this:

class WrapperShallow 
{
	private int[] a = new int[2];
 
 
 
	public void setArray()
	{
		a[0] = 7;
		a[1] = 17;
		a[2] = 77;
		for(int i = 0; i < 3; i++)
		{
        	System.out.println("Inital shallow object contain the numbers:\n");
        	System.out.print(a[i] + " ");
        }
 
	}
 
	public WrapperShallow (WrapperShallow ws)
	{
		a = ws.a;	
	}
 
	public String toString()
	{
		return Integer.toString(a[0]); 	
	}
 
	public boolean equal(WrapperShallow ws2)
	{
		return a.equals(ws2);
	}
 
 
}
 
 
 
class WrapperDeep
{
 
	private int[] a = new int[2];
 
	public void setArray()
	{
		a[0] = 7;
        a[1] = 17;
        a[2] = 77;
 
		for(int i = 0; i < 3; i++)
		{
			System.out.println("Inital shallow object contain the numbers:\n");
			System.out.print(a[i] + " ");
		}
	}
	public WrapperDeep(WrapperDeep wd)
	{
		a = new int[3];
 
		for (int i = 0; i < 3; i++)
			a[i] = wd.a[i];
	}
 
	public String toString()
 
	{
		return Integer.toString(a[0]); 
	}
 
	public boolean equal(WrapperDeep wd2)
	{
		return a.equals(wd2);
	}
 
 
}
 
 
 
 
 
public class WrapperDemo {
 
 
	public static void main(String[] args) 
	{
		WrapperShallow ws = new WrapperShallow();		
		ws.setArray();
 
 
	}
 
 
}

Just ignore the toString and Equals. I'll change those later.
The error I'm trying to understand is in this line "WrapperShallow ws = new WrapperShallow();"
I think I'm supposed to pass an array in the parentheses however I get an error every time I try to. I know I'm supposed to send something because it is supposed to receive something. Am I approaching this problem in the correct way? Any help would be greatly appreciated.

Thank you!

thanks for the reply.

Yeah that's what I am so confused about.

The instructions say to include this:

public WrapperShallow (WrapperShallow ws)
    {
        a = ws.a;  
    }

But like you said it's expecting a WrapperShallow to be sent to it. Do you think the instructor made a mistake? I'm not really sure what to do at this point. I might just send him an email and see if he can help me.

Thanks again.