Java loop over half of array

Question

I would like to loop over half of an array in Java; this is because the matrix will be completely symmetric. If I loop throw i columns and j rows, every time I do an operation of matrix[i][j] I will do the exact same operation to matrix[j][i]. I should be able to save time by not looping over half of the matrix. Any ideas on the easiest way to do this?

Answer 1

If you're trying to get a triangle:

for(int i=0; i<array.length; i++){
  for(int j=0; j<=i; j++){
    ..do stuff...
  }
}

Answer 2

for (i = 0;i < size; ++i) {
 for (j = 0; j < i; ++j) {
  result = do_operation(i,j);
  matrix[i][j] = result;
  matrix[j][i] = result ;
 }
}

So you invoke the operation method do_operation only once for each pair.