Hi Maha,
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?
- 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());"
- the implementation of CreateNewVector(size)
It seems likely it just does a "new twoIntegers[size];"
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.
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
