Using 'this' keyword in constructor

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:

Code:

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

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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!

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

Code:

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System.out.println(c);

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

kind regards,

Jos

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:

Code:

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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!

Quote:

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Originally Posted by 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:

Code:

---

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

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

Code:

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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.

Quote:

---

Originally Posted by kudwn

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

Code:

---

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.

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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