about array

[icube]

ok i have created a Customer class with get and set methods... (compiled ok)
i have also created another file which main is invoked...
in main i invoke a static method which i defined below the main method...
in this static method... i want to create an array of Customer...
so i did this...

Customer[] cusArr = new Customer[100];

but when i set it using

cusArr[0].setName("customer name");

it gave me a runtime error of nullpointerException at the above line...
what is wrong...? it compiled ok....

[ractoc]

with the statement Customer[] cusArr = new Customer[100]; you declared an array of Customer object. However, you still need to declare each object in the array seperately.
cusArr[0] = new Customer();
cusArr[0].setName("customer name");

[icube]

ok thks... figured that out... so the "new Customer[100]" line doesn't instantiate a instance of 100 Customer class... it just merely declaration eh..?

[ractoc]

Yeah, it instantiates the Array
But an Array is nothing more then a list of pointers. You will next have to tell the JVM where the pointers are pointing to. This is done with the actual instantiation of the new Customer();

Keeping this in mind, it might be a good idea to overload the constructor of the Customer class and create on e containing all the variables you wish to put in there.
Continuing your example, this would mean setting up the following constructor:

public Customer(String name)
{
setName(name);
}

This would enable you to instantiate and set the customer name in one method call:

casArr[0]=new Customer("customer name");