Using 'this' keyword in constructor

[kudwn]

So I've ran into a small problem here that I can't seem to get around. I'm writing a class Item and when the constructor is invoked, I need the Item to be added to an instance of another class Container. Here is the code for the constructor:

public Item(Container c) {
    c.add(this);
}

The problem is that I get a null pointer exception when calling the method add in for the Container. I think the problem lies in my using the 'this' keyword in the constructor, before the object has been fully constructed. Any ideas for getting around this?

Thanks!

[JosAH]

As the first line of your constructor print out 'c':

System.out.println(c);

I suspect that c is null; your 'this' reference is fine in a constructor.

kind regards,

Jos

[kudwn]

Actually my constructor is slightly more complex than this. I just simplified it a bit for ease of reading. It contains a line to ensure c is not null:

public Item(String description, Container c) {
    	if (c != null && c.find(description) == null) {
    		this.container = c;
    		this.description = description;
    		container.add(this);
    	}
}

Have any other ideas?

Thanks!

[JosAH]

Actually my constructor is slightly more complex than this. I just simplified it a bit for ease of reading. It contains a line to ensure c is not null:

public Item(String description, Container c) {
    	if (c != null && c.find(description) == null) {
    		this.container = c;
    		this.description = description;
    		container.add(this);
    	}
}

Have any other ideas?

Thanks!

Which line throws the NullPointerException? Even better: show us the entire stack trace.

kind regards,

Jos

[kudwn]

The null pointer exception occurs at line 22, which is the following:

container.add(this);

My original thought was that 'this' is being used as a parameter for a method of an external class before it has even been fully constructed. Would you know of a way to fully construct the Item first, and then add it to the Container?

I really appreciate your help.

[JosAH]

The null pointer exception occurs at line 22, which is the following:

container.add(this);

My original thought was that 'this' is being used as a parameter for a method of an external class before it has even been fully constructed. Would you know of a way to fully construct the Item first, and then add it to the Container?

I really appreciate your help.

Object 'this' already has been completely constructed; it may not be completely initialized yet but it already exists and can't be null. Check your member variable 'container'; it is probably the one that is null.

kind regards,

Jos