// Populate the header with SAMSequenceRecords
header.getSequenceDictionary().addSequence(new SAMSequenceRecord("chr1", 1000000));
// Create 2 alignments for each end of pair
final SAMFileWriter alignedWriter = factory.makeSAMWriter(header, false, alignedSam);
for (int i = 1; i <= 2; ++i) {
final SAMRecord firstOfPairAligned = new SAMRecord(header);
firstOfPairAligned.setReadName(firstOfPair.getReadName());
firstOfPairAligned.setReadBases(firstOfPair.getReadBases());
firstOfPairAligned.setBaseQualities(firstOfPair.getBaseQualities());