Maha and I went off-line and resolved this issue, which was just a Java
programming error.
Cheers,
--Matt
On Mar 17, 2011, at 4:41 PM, maha wrote:
Thanks for your time Matt. Below are my clarifications ...
> There are three things missing from your simplified code needed to give a
> definitive answer, so I'll infer them as follows:
> - the specification of "twoIntegers"
> "twoIntegers" seems to be a tuple of ints with get/set accessors, so it
> is an object (array of primitives?) not a primitive, right?
public class twoIntegers () {
private int x;
private int y;
.....
}
so it's not an array. That's why I didn't use the ArrayWritable
(although I tried but I didn't succeed).
> - in the exception
> "twoIntegersArrayWritable.readFields(twoIntegersArrayWritable.java:46)", what
> line 46 refers to
> I'm betting it refers to the line
> "this.vector[i].setFirstInteger(in.readInt());"
Yes it is . After some investigation, it turns that 'in' is empty at
this line, but it's because even though in the write function I have :
for(int i=0;i<this.vectorSize;i++)
out.writeInt( vector[i]. getFirstIntger());
out.writeInt( vector[i]. getSecondIneger());
but vectorSize is 0 ! so that's why nothing is written after vectorSize
into DataOutputStream in the first place to be read later :( although the
initialization of the class specifies clearly that the size is 10.
> - the implementation of CreateNewVector(size)
> It seems likely it just does a "new twoIntegers[size];"
Yes this is what I meant to do , because I wanted to make sure that my
array is not of size 0, but it's still of size zero.
>
> If the above is correct, then the problem is that standard Java behavior is
> to fill the new array with nulls rather than with empty twoInteger objects.
> So in readFields(), when you enter the loop to read values for vector, the
> code "this.vector[0]" fetches a null object, and the continuation
> "this.vector[0].setFirstInteger()" causes a NullPointerException.
>
Do you mean I have to use Integer objects instead of primitive types ??
> You can fix this in CreateNewVector(), by explicitly allocating a new
> twoInteger object for each location in the "vector" array, or in the
> readFields() loop, whichever suits your program semantics better.
>
> --Matt
>
>
> On Mar 17, 2011, at 2:04 PM, maha wrote:
>
> Hello,
>
> I'm stuck with this for two days now ...I found a previous post discussing
> this, but not with arrays.
>
> I know how to write Writable class with primitive type elements but this time
> I'm using an ARRAY of primitive type element, here it is in a simplified
> version for easy readability :
>
> public class twoIntegersArrayWritable implements Writable {
>
> private int vectorSize;
> private twoIntegers[] vector ;
>
> /* CONSTRUCTORS */ ===================================================
>
> twoIntegersArrayWritable () {}
>
> twoIntegersArrayWritable (int size, twoIntegers[] vec) {
> this.vectorSize = size;
> this.vector = vec;
> }
>
> /* WRITE FUNCTION */
> ===================================================
>
> public void write(DataOutput out) {
>
> out.writeInt(this.vectorSize);
> for(int i=0;i<this.vectorSize;i++){
> out.writeInt( vector[i]. getFirstIntger());
> out.writeInt( vector[i]. getSecondIneger());
> }
> }
>
> /* READ FUNCTION */
> ===================================================
>
> public void readFields(DataInput in) throws IOException {
>
> this.vectorSize = in.readInt();
> this.CreateNewVector (this.vectorSize);
> for(int i=0;i< this.vectorSize;i++){
> this.vector[i].setFirstInteger(in.readInt());
> this.vector[i].setSecondInteger(in.readInt());
> }
> }
> }
>
> The errors I get:
> java.lang.NullPointerException
> at twoIntegersArrayWritable.readFields(twoIntegersArrayWritable.java:46)
> at
> org.apache.hadoop.io.SequenceFile$Reader.getCurrentValue(SequenceFile.java:1751)
> at org.apache.hadoop.io.SequenceFile$Reader.next(SequenceFile.java:1879)
> at SequenceFileReader_Integers.main(SequenceFileReader_Integers.java:49)
>
> Or it would work fine but array size is always 0. So it won't read the
> integer fields.
>
> It would be helpful if someone already has an example of using array in their
> Writable class. I appreciate any thought.
>
> Maha
>
>
