simple java help

[laclac01]

I have attached code and was wondering if someone can help me though
it. I am just trying to make a simple database type program so i can
learn java. I know C++ well so i think i still need to get out of the
c++ mindset.
I get this error in eclipse "Exception in thread "main"
java.lang.NullPointerException
at allLists.AddName(allLists.java:12)
at server.main(server.java:20)"
I havent a clue what it means But i get the error when doing the
command
list[len].name = name;
in my addName method.
Why can't just do this and it work?

public static void main(String[] args)
{

ServerSocket s = null;
allLists list = new allLists();
list.AddName("jack","was","here");
try
{
s = new ServerSocket(SERVERPORT);
}
catch(IOException e)
{
System.out.println(e);
System.exit(1);
}

//while (true)
//{
Socket incoming = null;
try
{
incoming = s.accept();
}
catch(IOException e)
{
System.out.println(e);
// continue;
}

new inSocket(incoming, list).start();

//}


}

}






public class allLists
{
ResourceList[] list = new ResourceList[1000];
int len=0;

void AddName(String name, String IP, String reliability)
{
System.out.println(name);
System.out.println(len);
list[len].name = name;
len++;

}
void PrintName()
{
System.out.println(list[0].name);
}

public class ResourceList
{
public String name;
public String IP;
public String Reliability;

}

 

[Josef Kieser]

Hello,

I get this error in eclipse "Exception in thread "main"
java.lang.NullPointerException
at allLists.AddName(allLists.java:12)
at server.main(server.java:20)"
I havent a clue what it means But i get the error when doing the
command
list[len].name = name;
in my addName method.

You try to do something on an NULL-object.


This:

ResourceList[] list = new ResourceList[1000];

allocates memory for an array of ResourceList instances, but it does not
create those instances.
You need do something like this:

list[len] = new ResourceList();
list[len].name = name;
....

HTH,
Josef

 

[Trung Chinh Nguyen]

You forgot to call the constructor list[len] = new ResourceList();

 

[Mark Thomas]

I get this error in eclipse "Exception in thread "main"
java.lang.NullPointerException
at allLists.AddName(allLists.java:12)
at server.main(server.java:20)"
I havent a clue what it means But i get the error when doing the
command
list[len].name = name;
in my addName method.

You try to do something on an NULL-object.


This:

ResourceList[] list = new ResourceList[1000];

allocates memory for an array of ResourceList instances, but it does not
create those instances.
You need do something like this:

list[len] = new ResourceList();
list[len].name = name;
...

HTH,
Josef

And it would make it easier for java-types to understand your code if
you remembered that class names start with capital letters & variable
names start with lowercase letters.
Thanks

Mark