RUN TIME ERROR

Detailed Explanation in API document

http://java.sun.com/j2se/1.4.2/docs/api/java/lang/NullPointerException.html

In general, you would like to do something for an Object, but it is null

e.g. You would like to roll a dice, but the dice Object is null.

You have to initialise your variable to an instance of Object before use.

Dice yourDice;

int number = 0;

number = yourDice.roll(); // NullPointerException

yourDice = new Dice();

number = yourDice.roll(); // OK

rym82a at 2007-7-12 8:34:28 >

> Detailed Explanation in API document

> http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Null

> PointerException.html

>

> In general, you would like to do something for an

> Object, but it is null

> e.g. You would like to roll a dice, but the dice

> Object is null.

> You have to initialise your variable to an instance

> of Object before use.

>

> Dice yourDice;

> int number = 0;

> number = yourDice.roll(); // NullPointerException

> yourDice = new Dice();

> number = yourDice.roll(); // OK

Just to be a nitpicker...

The above code won't compile. Assuming that's inside a method, yourDice is a local variable, and therefore has no default value. It's not null--it's undefined. You'll get "yourDice may not have been intialized" ad the yourDice.roll() line when you try to compile. You'd need to add = null to the yourDice declaration.

If, on the other hand, yourDice is a member variable, then the statements number = ... etc. are not legal outside a method.

jverda at 2007-7-12 8:34:28 >