Incorrect use of System.nanoTime()

For example, to measure how long some code takes to execute:
 long startTime = System.nanoTime();
 // ... the code being measured ...
 long estimatedTime = System.nanoTime() - startTime; 

To compare two nanoTime values
 long t0 = System.nanoTime();
 ...
 long t1 = System.nanoTime();
one should use t1 - t0 < 0, not t1 < t0, because of the possibility of numerical overflow.