Throwing null pointer exception

Question

I am doing one application in android for that I need to access com.android.internal.telephony APIs. Now I am able to access those APIs but problem is wherever I call the

Answer 1

The method getEarliestConnection() makes a call to getConnections() which returns null.

Since getConnections() is abstract in Call check the method you've provided in MyCall.

Answer 2

Presumably getConnections() is returning null, so l is null, so trying to call l.size() is throwing the exception. We don't know what getConnections() does though.

Note that this looks suspicious too:

Connection myConn = new MyConn();
myConn = myCall.getEarliestConnection();

Why are you creating an instance of MyConn in the first line, only to throw it away again? Why not just use:

Connection myConn = myCall.getEarliestConnection();

In general, it's worth declaring local variables as late as you can, ideally when you have a useful value - so in your method, you could declare c within the loop, assign t a value in the declaration, declare l at the point of assignment, etc. You should also consider using generics where possible - e.g. List<MyConn> instead of just the raw List type.

EDIT: In contrast to the accepted answer, I would suggest changing getConnections() to always return a non-null value, returning an empty list if there are no connections. That will be easier to work with.

Answer 3

I think you forgot

CallManager cm;    
cm = new CallManager();

Answer 4

Obviously getConnections() returns null here and you cannot get the size of the null-object.

Here's how to fix it:

if (l == null || l.size() == 0) 
{
    return null;
}

So, if for some unknown reason, there is no Connection-List or the list is empty, null will be returned. Using the operator || will do the same as

if (l == null)
{
    return null;
}
else if ( l.size() == 0)
{
    return null;
}

Answer 5

You method

l = getConnections();

returns null, so your line 10 should look like: if (l==null) {

Answer 6

Your cm variable has been never initialized before getConnections() call. So, it is null and you get NullPointerException when trying to invoke cm.getActiveFgCall().