Multidimensional Array to Set

[steelodon]

Set<String> PropType = new HashSet<String>();

for (int j = 0; j < cols; j++){
PropType.add(line[1][j]);
}

Iterator Prop = PropType.iterator();

while(Prop.hasNext()){
System.out.print(Prop.next());
}

Tried to run this code...but it keeps giving the error:

Exception in thread "main" java.lang.NullPointerException

Any suggestions?

 

[purbeast0]

im guessing since you left other code out that it is happening somewhere else.

that code you have there looks like it shouldn't throw any null pointer exception.

when you get the exception, look at the thread stack and it will give you a line number and file where the null pointer exception happens.

 

[TheRyuu]

Probably time to show the debugger a little love.

With the visual debugging tools in Eclipse or Netbeans it should make it a breeze.

 

[Net]

if your sure its from this block of code then it would be this line

PropType.add(line[1][j]);

being evaluated as

PropType.add(null);

 

[purbeast0]

if your sure its from this block of code then it would be this line

PropType.add(line[1][j]);

being evaluated as

PropType.add(null);

you can add a null value to a hashset and it won't throw an exception.

 

[Crusty]

you can add a null value to a hashset and it won't throw an exception.

right, but if line[1] doesn't exist [j] will throw.

 

[Ken g6]

right, but if line[1] doesn't exist [j] will throw.

Say, given that, the first loop could be replaced by:

[spoiler]Set<String> PropType = new HashSet<String>(Arrays.asList(line[1]));[/spoiler]

Couldn't it? (Code in spoiler in case this is homework or something.)

 

[purbeast0]

right, but if line[1] doesn't exist [j] will throw.

pretty sure that will throw an index out of bounds exception, not a null pointer exception.

 

[iCyborg]

http://download.oracle.com/javase/1.4.2/docs/api/java/util/Set.html#add(java.lang.Object)

Seems it depends on Set implementation whether it will throw NullPointerException for add.

 

[purbeast0]

http://download.oracle.com/javase/1.4.2/docs/api/java/util/Set.html#add(java.lang.Object)

Seems it depends on Set implementation whether it will throw NullPointerException for add.

yah, the hashset should be able to handle adding a null value fine.

http://download.oracle.com/javase/1.4.2/docs/api/java/util/HashSet.html#add(java.lang.Object)

 

[Crusty]

pretty sure that will throw an index out of bounds exception, not a null pointer exception.

What if you set lines[1] = null? Maybe I wasn't quite clear, but if its possible to put a null in the collection it's also possible to get one out. Setting index 1 to null is different than never setting index 1.

 

[purbeast0]

What if you set lines[1] = null? Maybe I wasn't quite clear, but if its possible to put a null in the collection it's also possible to get one out. Setting index 1 to null is different than never setting index 1.

ah yea gotcha, that makes sense. that would definitely toss out a null pointer exception.

which makes me wonder why he didn't post the rest of his code along with this error.

 

[iCyborg]

I wonder why he didn't post more of the stack backtrace. Usually the next few lines are far more revealing...