Java for loops null pointer

Question

I have the class Memory which is a list of blocks, and Blocks which is a list of tuples and Tuple.

Memory m;
for(Block b:m.blocklist){
    for (Tuple t:b.tuplelist){
        //do something
    }
}

The above code works fine, every single tuple goes through it but the problem is even after the last tuple, it continues on leading to a null pointer exception. I can't modify the memory class, blocks nor tuples so how do I avoid the error?

Would it help to check if the block or tuple you get from the list is null? — Joni
– Joni, Commented Oct 23, 2014 at 9:43
Thanks for the help. Could've sworn I tried this myself but for some reason it didn't work "-_- — TheWatisit
– TheWatisit, Commented Oct 23, 2014 at 10:20

Olimpiu POP · Accepted Answer · 2014-10-23 09:46:05Z

1

Supposing that the NPE appears on the line of the second for you can add a check for null:

Memory m;
for(Block b:m.blocklist){
   if (b != null) {
     for (Tuple t:b.tuplelist){
        //do something
      }
   }
 }

answered Oct 23, 2014 at 9:46

Olimpiu POP

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Bohemian · Accepted Answer · 2014-10-23 09:44:02Z

0

If one of the blocks is null, you'll get an NPE.

Check for null:

Memory m;
for(Block b:m.blocklist){
    if (b != null) {
        for (Tuple t:b.tuplelist){
            //do something
        }
    }
}

answered Oct 23, 2014 at 9:44

Bohemian♦

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Comments

NewOutlaw · Accepted Answer · 2014-10-23 10:01:06Z

0

Perhaps in the last Blocklist the Tuplelist is null?

answered Oct 23, 2014 at 10:01

NewOutlaw

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